Papers - KIWA Toshihiko

Mapping Surface Potential in DNA Aptamer–Neurochemical and Membrane–Ion Interactions on the SOS Substrate Using Terahertz Microscopy

Kosei Morita, Yuta Mitsuda, Sota Yoshida, Toshihiko Kiwa, Jin Wang

Biosensors   2025.1

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/bios15010046

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Precise Cancellation of Magnetic Signal Using a Movable Ferromagnetic Rod for Magnetic Nanoparticles Measurements

Rikako Ogawa, Kei Yamashita, Jin Wang, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   45 - 46   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877348

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Development of Viscosity Measurement System Utilizing the Frequency Characteristics of Magnetic Nanoparticles

Kei Yamashita, Kosuke Naito, Rikuya Korenaga, Jin Wang, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   21 - 24   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877308

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Development of an AC Magnetic Characterization System and Its Application to Magnetic Immunoassay

Rikuya Korenaga, Kei Yamashita, Kosuke Naito, Jin Wang, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   29 - 32   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877314

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Terahertz spectroscopic characterization of fractal silver nanoparticles

Hiroya Tanaka, Sota Itayama, Tomoki Kawahara, Jin Wang, Nobuyuki Takeyasu, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   37 - 39   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877289

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Measuring Biotin Concentrations for Quantitative Magnetic Immunoassay Using a Femtosecond Laser

Shu Asayama, Sakuya Kako, Kei Yamashita, Jin Wang, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   40 - 41   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877344

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Improved waterproof performance of ultra-thin Pt film hydrogen sensors with a glass package

Yuki Oh, Haruhito Nakayama, Jin Wang, Toshihiko Kiwa

2024 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE)   42 - 44   2024.12

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/apace62360.2024.10877373

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Microdetection of Nucleocapsid Proteins via Terahertz Chemical Microscope Using Aptamers

Xue Ding, Mana Murakami, Jin Wang, Hirofumi Inoue, Toshihiko Kiwa

Sensors   2024.11

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/s24227382

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Label-Free Measurement of CD63 Positive Extracellular Vesicles Using Terahertz Chemical Microscopy

Changjiang Liu, Jin Wang, Ryo Negishi, Tatsutoshi Inuzuka, Toshihiko Kiwa

ACS Sensors   2024.5

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acssensors.4c00590

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Backside Defect Evaluation in Carbon Steel Plate Using a Hybridized Magnetic Flux Leakage and Eddy Current Technique

Mohd Aufa Hadi Putera Zaini, Mohd Mawardi Saari, Nurul A’in Nadzri, Zulkifly Aziz, Toshihiko Kiwa

Journal of Nondestructive Evaluation   2024.3

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Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10921-023-01022-z

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Ultrathin Platinum Film Hydrogen Sensors with a Twin-T Type Notch Filter Circuit

Shoki Wakabayashi, Yuki Oh, Haruhito Nakayama, Jin Wang, Toshihiko Kiwa

Sensors   2024.1

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/s24020548

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Comparative Study of Terahertz Chemical Microscopy and Flexible ISFET Approaches for Calcium Ion Detection

Sota Yoshida, Jin Wang, Kenji Sakai, Toshihiko Kiwa

2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)   2023.9

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/irmmw-thz57677.2023.10299237

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Detection of Nucleocapsid Proteins of COVID-19 using a Terahertz Chemical Microscope

Xue Ding, Sayaka Tsuji, Mana Murakami, Jin Wang, Hirofumi Inoue, Toshihiko Kiwa

2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)   2023.9

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/irmmw-thz57677.2023.10298956

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Special Issue “Terahertz (THz) Science in Advanced Materials, Devices and Systems”

Toshihiko Kiwa, Masayoshi Tonouchi

Photonics   2023.9

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/photonics10091024

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Special Issue “Terahertz (THz) Science in Advanced Materials, Devices and Systems”

Toshihiko Kiwa, Masayoshi Tonouchi

Photonics   2023.9

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/photonics10091024

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Multifunctional terahertz microscopy for biochemical and chemical imaging and sensing

Jin Wang, Masaki Ando, Hiroki Nagata, Sota Yoshida, Kenji Sakai, Toshihiko Kiwa

Biosensors and Bioelectronics   220   114901 - 114901   2023.1

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.bios.2022.114901

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All-in-One terahertz taste sensor: integrated electronic and bioelectronic tongues

Jin Wang, Kenji Sakai, Toshihiko Kiwa

Sensors & Diagnostics   2023

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Taste sensors, also known as electronic tongues or bioelectronic tongues, are designed to evaluate food and beverages, as well as for medical diagnostics. This device mimics the ability of the...

DOI： 10.1039/d3sd00038a

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Aggregation of magnetic nanoparticles in biological solvents evaluated by HTS-SQUID magnetic immunoassay system

K. Yamashita, K. Kishimoto, H. Kuroda, J. Wang, K. Sakai, M. M. Saari, T. Kiwa

IEEE Transactions on Applied Superconductivity   33 ( 5 )   1 - 6   2023

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tasc.2023.3239830

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Magnetic-Particle-Discrimination Method Using Difference of Relaxation Time for Magnetic Particle Imaging

Kota Nomura, Masaomi Washino, Tetsuya Matsuda, Shun Tonooka, Seino Satoshi, H. Yoshida, K. Nishigaki, Takashi Nakagawa, Toshihiko Kiwa

IEEE Magnetics Letters   2023

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Publishing type：Research paper (scientific journal)  

DOI： 10.1109/LMAG.2023.3243493

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Thickness Measurement at High Lift-Off for Underwater Corroded Iron-Steel Structures Using a Magnetic Sensor Probe

Shoya Adachi, Minoru Hayashi, Taisei Kawakami, Yuto Ando, Jin Wang, Kenji Sakai, Toshihiko Kiwa, Toshiyuki Ishikawa, Keiji Tsukada

Sensors   2022.12

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/s23010380

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Thickness Measurement at High Lift-Off for Underwater Corroded Iron-Steel Structures Using a Magnetic Sensor Probe

Shoya Adachi, Minoru Hayashi, Taisei Kawakami, Yuto Ando, Jin Wang, Kenji Sakai, Toshihiko Kiwa, Toshiyuki Ishikawa, Keiji Tsukada

Sensors   2022.12

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/s23010380

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Dispersion of Fe₃O₄ Nanoparticle Beads Driven by Femtosecond Laser Pulses for Quantitative Magnetic Immunoassay Measurements

Kouhei Kishimoto, Hiroto Kuroda, Misaki Tsubota, Kei Yamashita, Jin Wang, Kenji Sakai, Mohd Mawardi Saari, Toshihiko Kiwa

ACS Applied Nano Materials   5 ( 11 )   17258 - 17263   2022.11

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsanm.2c04399

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Electric Potential Mapping of All-Solid-State Lithium Ion Batteries using A Terahertz Chemical Microscope

Ryota Tomie, Taketo Yamaguchi, Masashi Shimizu, Kashu Hamada, Takashi Teranishi, Hidetoshi Nose, Masaki Kobayashi, Jin Wang, Kenji Sakai, Toshihiko Kiwa

2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz)   2022.8

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/irmmw-thz50927.2022.9896121

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Terahertz Chemical Microscope for Calcium Ions and Stress Biomarker Sensing

Jin Wang, Sota Yoshida, Masaki Ando, Kenji Sakai, Toshihiko Kiwa

2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz)   2022.8

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/irmmw-thz50927.2022.9895468

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Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data

Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Micromachines   2022.8

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/mi13081352

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Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data

Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Micromachines   2022.8

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/mi13081352

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Rational Design of Peptides Derived from Odorant-Binding Proteins for SARS-CoV-2-Related Volatile Organic Compounds Recognition

Jin Wang, Kenji Sakai, Toshihiko Kiwa

Molecules   27 ( 12 )   3917 - 3917   2022.6

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Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

DOI： 10.3390/molecules27123917

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Rational Design of Peptides Derived from Odorant-Binding Proteins for SARS-CoV-2-Related Volatile Organic Compounds Recognition

Jin Wang, Kenji Sakai, Toshihiko Kiwa

Molecules   2022.6

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/molecules27123917

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A Versatile Terahertz Chemical Microscope and Its Application for the Detection of Histamine

Jin Wang, Kosuke Sato, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

Photonics   2022.1

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/photonics9010026

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A Versatile Terahertz Chemical Microscope and Its Application for the Detection of Histamine

Jin Wang, Kosuke Sato, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

Photonics   2022.1

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Publishing type：Research paper (scientific journal)  

DOI： 10.3390/photonics9010026

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Crack Detection for Welded Joint with Surface Coating Using Unsaturated AC Magnetic Flux Leakage

Minoru Hayashi, Taisei Kawakami, Shoya Adachi, Jin Wang, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada, Yohei Miyamoto, Mikihito Hirohata, Toshiyuki Ishikawa

IEEE Transactions on Magnetics   1 - 1   2022

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tmag.2022.3151656

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Development of impedance measurement of lithium ion batteries electrode using terahertz chemical microscope

Masashi Shimizu, Ryoji Yamanaka, Takashi Teranishi, Jin Wang, Kenji Sakai, Keiji Tsukada, Toshihiko Kiwa

Electrical Engineering in Japan   214 ( 4 )   2021.12

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/eej.23355

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/eej.23355

Visualization of Charge-Transfer Complex for the Detection of 2,4,6-Trinitrotoluene Using Terahertz Chemical Microscope

Jin Wang, Hiroki Nagata, Masaki Ando, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

JOURNAL OF THE ELECTROCHEMICAL SOCIETY   168 ( 11 )   2021.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

This study focuses on the visualization of a charge-transfer complex, namely a Meisenheimer complex, for the detection of uncharged 2,4,6-trinitrotoluene (TNT) explosives by developing a terahertz chemical microscope (TCM) imaging system. The organic amine 3-aminopropyltriethoxysilane (APTES) was immobilized on an SiO2-film-coated TCM sensing plate, where it interacted with TNT molecules. The surface electrical potential distribution of TNT, APTES, and the charge-transfer complex was mapped. An electrical potential shift occurred due to the formation of a charge-transfer complex between the electron-rich amino-silane APTES and electron-deficient TNT molecules on the surface of the sensing plate. The electrical imaging and detection of TNT explosives by using the TCM imaging system were demonstrated by measuring the amplitude of the terahertz pulse caused by this electrical potential shift. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane and N1-(3-trimethoxysilylpropyl)diethylenetriamine were used for further evaluation and comparison of color changes arising from the amine-TNT interactions. The results have shown that TCM imaging is a promising method for the detection of uncharged TNT explosives at a low (sub-parts-per-million) concentration.

DOI： 10.1149/1945-7111/ac3a2c

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Design and validation of microfluidic parameters of a microfluidic chip using fluid dynamics

Feroz Ahmed, Yuichi Yoshida, Jin Wang, Kenji Sakai, Toshihiko Kiwa

AIP ADVANCES   11 ( 7 )   2021.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

The internal fluidic parameters of microfluidic channels must be analyzed to solve fundamental microfluidic problems, including microscale transport problems involving thermal analysis, chemical reactivity, velocity, pressure drop, etc., for developing good-quality chemical and biological products. Therefore, the characterization and optimization of the interaction of chemical and biological solutions through microfluidic channels are vital for fluid flow design and engineering for quality assurance in microfluidic platforms. As the internal structures and kinetics of microfluidic channels are becoming increasingly complex, experiments involving optimal fluidic and transport designs are challenging to perform with high accuracy. However, highly integrated simulation tools can guide researchers without specialized computational fluid backgrounds to design numerical prototypes of highly integrated devices. In this study, a microfluidic chip with two inlet wells and one outlet well was fabricated from polydimethylsiloxane following which simulations were performed using an ANSYS Fluent tool influenced by computational fluid dynamics at a nearly identical scale. The pressure drop and velocity profiles of the interaction of two pH buffer solutions (pH 4 and 10) through the designed microfluidic chip were qualitatively estimated from experimental data analysis and validated with the simulation results obtained from the CFD-influenced ANSYS Fluent tool. (c) 2021 Author(s).

DOI： 10.1063/5.0056597

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Noninvasive, label-free, and quantitative monitoring of lipase kinetics using terahertz emission technology

Sharifun Nahar, Ahmed Mohamed, Xavier Ropagnol, Amir Hassanpour, Toshihiko Kiwa, Tsuneyuki Ozaki, Marc A. Gauthier

BIOTECHNOLOGY AND BIOENGINEERING   118 ( 11 )   4246 - 4254   2021.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Enzymes catalyze chemical transformations of great importance in many fields, and analysis of the rate of these transformations is equally important. The latter are typically monitored using surrogate substrates that produce quantifiable optical signals, owing to limitations associated with "label-free" techniques that could be used to monitor the transformation of original substrate molecules. In this study, terahertz (THz) emission technology is used as a noninvasive and label-free technique to monitor the kinetics of lipase-induced hydrolysis of several substrate molecules (including the complex substrate whole cow's milk) and horseradish peroxidase-catalyzed oxidation of o-phenylenediamine in the presence of H2O2. This technique was found to be quantitative, and kinetic parameters are compared to those obtained by proton NMR spectroscopy or UV/Vis spectroscopy. This study sets the stage for investigating THz emission technology as a tool for research and development involving enzymes, and for monitoring industrial processes in the food, cosmetic, detergent, pharmaceutical, and biodiesel sectors.

DOI： 10.1002/bit.27893

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Properties of single- and multi-core magnetic nanoparticles assessed by magnetic susceptibility measurements

Mohd Mawardi Saari, Mohd Herwan Sulaiman, Nurul Akmal Che Lah, Zulkifly Aziz, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   528   2021.6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Characterization of structural and magnetic properties of MNP ensembles is crucial in tailoring their performance for biomedical applications. In this work, we evaluate the size distribution of magnetic cores in single- and multi-core nanoparticles in water suspension using transmission electron microscopy (TEM) and static magnetization curve, with the geometrical core size ranges from 8.3 to 40.2 nm. A reasonable core size derived from the magnetization curve is obtained in comparison to the geometrical size from TEM image. The magnetic moment distribution possibly reveals that the reduction of effective magnetic core size is due to the magnetization degradation in cores. The hydrodynamic size and average anisotropy energy ratio obtained from the AC susceptibility response of MNPs from 5 Hz to 100 kHz are also evaluated. The complex distribution of relaxation time is constructed by applying a non-negative least square method to an AC susceptibility model that incorporates the inter- and intra-potential-well contributions. It is found that a log-normal distribution might not be adequate to represent the hydrodynamic size distribution reconstructed from the AC susceptibility responses of the suspended samples. It is demonstrated that the AC susceptibility model used in this study can be used to fairly estimate the average anisotropy energy ratio for MNP ensembles dominated by thermally blocked particles. Moreover, it can be suggested that besides the geometrical core size, the degree of core aggregation also plays an important role in determining the anisotropy energy ratio and effective magnetic moment.

DOI： 10.1016/j.jmmm.2021.167812

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Evaluation of penetration speed of liquids into skin using a terahertz time-of-flight method

Sota Sueda, Tomoya Niki, Kenji Sakai, Toshihiko Kiwa

JAPANESE JOURNAL OF APPLIED PHYSICS   60 ( 3 )   2021.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Analyzing the penetration of cosmetic/medical lotions and creams into the skin is important for evaluating their effectiveness. Hence, the penetration speed of liquids into chicken and pig skins was evaluated using a terahertz (THz) time-of-flight method. An arsenide-free disposable THz emitter comprising a silicon film on a sapphire substrate was developed for practical measurements using skin samples. The skin sample was mounted on the THz emitter surface directly so that the generated THz pulses in the silicon film were easily focused on the skin sample. To evaluate the time evolution of the penetration depth, the arrival times of the reflected THz pulses at the edge of the liquid-penetrated region on the skin were observed. As a preliminary experiment, measurements using a stack of conventional glass slides were conducted. In addition, the penetration speed into the chicken and pig skin was compared to prove the practical applicability of our method.

DOI： 10.35848/1347-4065/abdd03

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Terahertz imaging technique for monitoring the flow of buffer solutions at different pH values through a microfluidic chip

Feroz Ahmed, Atsuya Mahana, Katsuya Taniizumi, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Japanese Journal of Applied Physics   60 ( 2 )   2021.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2021 The Japan Society of Applied Physics Polydimethylsiloxane (PDMS)-based mold prepared using a 3D-printed structure is a cost-effective material and tool to fabricate robust microfluidic chips (MCs) without requiring expensive clean room facilities. A capillary-based MC made of PDMS can be attached onto a glass substrate to visualize the chemical reactions in different types of pH buffer solutions (BSs) flowing through microflow channels (MFCs) using terahertz (THz) image sensing technology. In this study, we designed a microfluidic structure with two inlet wells and an outlet well, equipped with a Si:sapphire substrate to visualize the chemical interaction between BSs injected at different pH values (4 and 10) through an MFC. THz imaging maps were captured during the flow of the BSs using a THz chemical microscope, and the fluid dynamics was studied. We determined and plotted the variation in the THz amplitude data with respect to the BS concentration and analyzed the characteristics of the data.

DOI： 10.35848/1347-4065/abd86e

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Imaging of Defect Signal of Reinforcing Steel Bar at High Lift-Off Using a Magnetic Sensor Array by Unsaturated AC Magnetic Flux Leakage Testing

Minoru Hayashi, Taisei Kawakami, Taisuke Saito, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Magnetics   57 ( 2 )   2021.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

© 1965-2012 IEEE. Reinforcing steel bars (rebars) in the concrete need to be inspected to prevent the structure from collapsing. Magnetic nondestructive testing methods can inspect the rebar without the influence of concrete. However, since the inspection is performed at a high lift-off on concrete, a strong applied magnetic field is required in order to measure a sufficient magnetic signal generated from the rebar. In addition, if a single sensor is used to measure the rebar, this requires the scanning of extensive area along the invisible rebar covered with the concrete. To overcome these problems, we have developed a method to detect and image the defect signal using unsaturated ac magnetic flux leakage (USAC-MFL) testing combining a magnetic sensor array probe. The USAC-MFL is a method that uses an alternating magnetic field in the initial magnetization characteristics of steel, which does not require a strong applied magnetic field compared to the conventional MFL method. By measuring the magnetic flux from the rebar in a wide area using the magnetic sensor array probe, the defect signal was able to be detected and imaged. The defect signal was able to be confirmed up to the lift-off of 100 mm even when the defect was half length of the rebar or located on the back side.

DOI： 10.1109/TMAG.2020.3017722

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A sensitive magnetometer utilizing high-T <inf>c</inf> SQUID for magnetic property characterization

Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Microsystem Technologies   27 ( 9 )   3413 - 3420   2021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature. Magnetometer is one of the indispensable instruments utilized for the magnetic property characterization of materials, where it evaluates the magnetic response originated from the materials. The non-invasive magnetic technique has promoted magnetometer to be utilized in new applications such as in biomedical applications. In this work, we report the development of a magnetometer utilizing a high critical temperature superconducting quantum interference device (high-Tc SQUID) and a flux transformer composed of an induction coil. The high-Tc SQUID is used in order to realize high sensitivity, compact, and low-running cost magnetometer for biomedical applications such as characterization of magnetic nanoparticles. A first-order planar gradiometer with a compensation coil was used as the detection coil to achieve high sensitivity and cancellation factor. We fabricate an electromagnet with primary and small secondary excitation coils to enable a wide range of the excitation magnetic field with a high resolution. To reduce the magnetic field’s drift, we apply a digital feedback program to control the electrical current of the electromagnet. The performance of the developed system is demonstrated by measuring the magnetization curve and AC responses of an iron oxide composite sample. The sensitivity showed by the developed magnetometer reveals its potential for a highly sensitive magnetic property characterization.

DOI： 10.1007/s00542-020-05198-6

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Investigation of Cross-Section Measurement Method for All-Solid-State Batteries Using Terahertz Chemical Microscopy

Masashi Shimizu, Ryota Tomie, Kashu Hamada, Takashi Teranishi, Jin Wang, Kenji Sakai, Toshihiko Kiwa

2021 46TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES (IRMMW-THZ)   2021

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In recent years, all-solid-state batteries have been attracting attention as secondary batteries to replace Li ion batteries. To improve the performance of all-solid-state batteries, measurement methods are required to evaluate electrode-solid electrolyte interfaces and electrochemical reactions between electrodes. In this study, we investigated a measurement method for the cross-section of all-solid-state batteries using terahertz chemical microscopy (TCM). We fabricated a model of all-solid-state battery and showed the possibility of using TCM to measure the cross-section of the all-solid-state battery by measuring the cross-section of a model of all-solid-state battery.

DOI： 10.1109/IRMMW-THz50926.2021.9567015

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Development of Ion Concentration Measurement Method for Minute Volume of Blood Using Terahertz Chemical Microscope

Katsuya Taniizumi, Hiroki Nagata, Masaki Ando, Atsuya Mahana, Jin Wang, Kenji Sakai, Toshihiko Kiwa

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2021-August   2021

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Publishing type：Research paper (international conference proceedings)  

A terahertz chemical microscope (TCM) was proposed and developed to measure small ion concentrations in solution. By creating multiple wells on the sensing plate, it was possible to measure the ion concentration of 35 μl of whole sheep blood.

DOI： 10.1109/IRMMW-THz50926.2021.9566818

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Electric Potential Distribution on Lithium Ion Battery Cathodes Measured Using Terahertz Chemical Microscopy

Toshihiko Kiwa, Yuki Akiwa, Hayato Fujita, Takashi Teranishi, Kenji Sakai, Hidetoshi Nose, Masaki Kobayashi, Keiji Tsukada

Journal of Infrared, Millimeter, and Terahertz Waves   41 ( 4 )   430 - 437   2020.4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. A terahertz chemical microscope has been developed to visualize electric potential distribution on lithium ion battery cathodes during battery operation. A sensing plate comprising a Si film grown epitaxially on a sapphire substrate was used as a terahertz emitter. The amplitude of terahertz radiation from the sensing plate could be related to the electric potential at the exact point where a femtosecond laser illuminated. Here, the sensing plate was integrated into a conventional can-type lithium ion battery and terahertz radiation from the sensing plate was observed during battery operation between 2.7 and 4.2 V. By scanning the laser, the distribution of terahertz amplitude radiated from the sensing plate was observed, which could be related to the electric potential distribution on the electrodes of the batteries. Localized electric potential could be visualized as the amplitude of terahertz radiation generated in the sensing plate, which was integrated beneath the battery electrode.

DOI： 10.1007/s10762-019-00640-x

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Liquid-like dielectric response is an origin of long polaron lifetime exceeding 10 μs in lead bromide perovskites. International journal

Kiyoshi Miyata, Ryota Nagaoka, Masaki Hada, Takanori Tanaka, Ryuji Mishima, Taihei Kuroda, Sota Sueta, Takumi Iida, Yoshifumi Yamashita, Takeshi Nishikawa, Kenji Tsuruta, Yasuhiko Hayashi, Ken Onda, Toshihiko Kiwa, Takashi Teranishi

The Journal of chemical physics   152 ( 8 )   084704 - 084704   2020.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Lead halide perovskites are promising materials for optoelectronic applications because of their exceptional performances in carrier lifetime and diffusion length; however, the microscopic origins of their unique characteristics remain elusive. The organic-inorganic hybrid perovskites show unique dielectric functions, i.e., ferroelectric-like phonon responses in the 0.1-10 THz region and liquid-like rotational relaxation in the 1-100 GHz range. To reveal the role of the dielectric responses is of primal importance because the dielectric screening is a key to understanding the optoelectronic properties governed by polarons in the perovskites. Here, we conducted comparative studies of broadband dielectric spectroscopy on both all-inorganic CsPbBr3 and organic-inorganic hybrid (CH3NH3)PbBr3 single crystals to uncover the origin of the liquid-like dielectric relaxation in the 1-100 GHz range. We confirmed the absence of the dielectric response in the range of 106-1010 Hz in CsPbBr3, which was clearly present in the hybrid (CH3NH3)PbBr3. This suggests that the response is almost purely due to the rotational motions of the organic dipoles in the hybrid perovskites. We evaluated the lifetimes of the polarons using surface-free transient photoluminescence. The lifetime in CsPbBr3 was up to 1.6 µs, while the lifetime in (CH3NH3)PbBr3 was 18 µs. The lifetime in the hybrid (CH3NH3)PbBr3 was significantly longer than in CsPbBr3, also confirmed by transient infrared spectroscopy. We concluded that the liquid-like dielectric response inhibits polaron recombination due to the efficient separation of opposite charges by the additional dynamic disorder.

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Laser monitoring of dynamic behavior of magnetic nanoparticles in magnetic field gradient

Kenta Tsunashima, Katsuya Jinno, Bunta Hiramatsu, Kayo Fujimoto, Kenji Sakai, Toshihiko Kiwa, Mohd Mawardi Saari, Keiji Tsukada

AIP Advances   10 ( 1 )   2020.1

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© 2020 Author(s). Manipulation of magnetic nanoparticles (MNP) by an external magnetic field has been widely studied in the fields of biotechnology and medicine for collecting and/or reacting biomaterials in the solutions. Here, dynamic behaviors of MNP in solution under changing gradient magnetic field were investigated using our newly developed laser transmission system (LTS) with a variable magnetic field manipulator. The manipulator consists of a moving permanent magnet placed beside the optical cell filled with MNP solution. A laser beam was focused on the cell and the transmitted laser beam was detected by a silicon photodiode, so that the localized concentration of the MNP at the focused area could be evaluated by the intensity of transmitted laser beam. In this study, the LTS was applied to evaluate dynamic behaviors of MNP in serum solution. Dispersion and aggregation of MNP in the solution were evaluated. While time evolution of dispersion depends on the serum concentration, the behavior during aggregation by the magnetic field was independent of the serum concentration. A series of measurements for zeta-potentials, distributions of particle size, and magnetization distributions was carried out to understand this difference in the behavior. The results indicated that a Brownian motion was main force to distribute the MNP in the solution; on the other hand, the magnetic force to the MNP mainly affected the behavior during aggregation of the MNP in the solution.

DOI： 10.1063/1.5130167

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Magnetic characterization change by solvents of magnetic nanoparticles in liquid-phase magnetic immunoassay

Katsuya Jinno, Bunta Hiramatsu, Kenta Tsunashima, Kayo Fujimoto, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

AIP Advances   9 ( 12 )   2019.12

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© 2019 Author(s). Liquid-phase magnetic immunoassay (MIA) using magnetic nano-particles (MNPs) has been studied as a more rapid method compared to optical methods for inspecting proteins and viruses. MIA can estimate the number of conjugated antibodies without being washed differently from conventional optical immunoassay. However, in the case of the liquid phase, it is considered that the magnetic properties of MNPs are affected by physical properties such as viscosity and impurity substances such as biological substances contained in the blood. In this study, the effect of sodium chloride (NaCl) in buffer and serum solution was evaluated to reveal the effect of serum because the sodium (Na+) and chloride (Cl-) ions in the serum dominate ion balance of blood. The measurement results of AC magnetic susceptibility and a dynamic light scattering (DLS) showed that the aggregation of MNPs was largely affected by the concentration of NaCl. This effect of the NaCl could be explained by shielding of the surface charge of MNPs by ions in the solution. Although the concentrations of NaCl in the buffer and serum solution were almost same, we found that MNPs were aggregated more in their size for those in the serum solution because of other impurities, such as proteins. These results suggest evaluation of effects of the contaminants in serum and optimization of polymer coatings of MNPs could be important factors to realize measurements of magnetic immunoassay with high accuracy.

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One-Minute Joule Annealing Enhances the Thermoelectric Properties of Carbon Nanotube Yarns via the Formation of Graphene at the Interface Reviewed

Masaki Hada, Taisuke Hasegawa, Hirotaka Inoue, Makito Takagi, Kazuki Omoto, Daiki Chujo, Shogo Iemoto, Taihei Kuroda, Taiga Morimoto, Takuma Hayashi, Toru Iijima, Tomoharu Tokunaga, Naoshi Ikeda, Kazuhiro Fujimori, Chihiro Itoh, Takeshi Nishikawa, Yoshifumi Yamashita, Toshihiko Kiwa, Shin ya Koshihara, Satoshi Maeda, Yasuhiko Hayashi

ACS Applied Energy Materials   2 ( 10 )   7700 - 7708   2019.10

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© 2019 American Chemical Society. Interfaces in nanocarbon materials are highly important, as they determine the properties of carbon-based devices. In terms of carrier and thermal transport properties, the interfacial features are often more important than the intrinsic characteristics. Herein, we describe how 1 min Joule annealing of carbon nanotube (CNT) yarns can convert the interfacial amorphous carbon into graphene fragments. After 1 min Joule annealing, we have obtained multiwalled CNT yarns with extremely high Seebeck coefficients (±100 μV/K) and high thermoelectric power factor (400 and 1000 μW/mK2) at room temperature, both with or without polyethylenimine doping. Theoretical simulations and experimental measurements helped to determine the optimal annealing conditions in terms of a rapid transformation of the interfacial amorphous carbon between the bundled CNTs in the yarn into graphene fragments at â¼2000 K. The present approach represents significant progress in energy materials science, as it provides a guiding principle for the design of interfaces in nanocarbon materials with potential applications in energy-harvesting systems.

DOI： 10.1021/acsaem.9b01736

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Influence of Viscosity on Dynamic Magnetization of Thermally Blocked Iron Oxide Nanoparticles Characterized by a Sensitive AC Magnetometer

Mohd Mawardi Saari, Nazatul Shareena Suhaimi, Mohd Herwan Sulaiman, Nurul Akmal Che Lah, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Superconductivity and Novel Magnetism   32 ( 9 )   2765 - 2772   2019.9

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© 2019, Springer Science+Business Media, LLC, part of Springer Nature. In this work, we show that the viscosity of carrier liquid affects the dynamic magnetization of thermally blocked multi-core iron oxide nanoparticles. The core size of the nanoparticles was determined from the magnetization curve measured by a specially developed high-Tc SQUID magnetometer and calculated to be 11.7 nm. Using an AC magnetometer developed based on induction coils, the dynamic magnetization of the multi-core iron oxide nanoparticle solution was measured from 3 Hz to 10.48 kHz. Later, we reconstructed of the hydrodynamic size distribution of the particles by assuming a log-normal distribution of particle size in an AC susceptibility model by Shliomis and Stepanov, which accounts for anisotropic directions of the easy axes of magnetic nanoparticles with respect to the excitation field direction. The reconstructed hydrodynamic sizes showed an average diameter of 130 nm and agreed with the size determined by dynamic light scattering method. In the case of increasing viscosity of the carrier liquids from 0.89 to 8.11 mPa s, the dynamic magnetization peaks of the imaginary component have shifted to a lower frequency region. We showed that the harmonics ratio and phase delay upon the magnetic field excitation at 30 Hz could also be used to determine the viscosity of carrier liquid independently.

DOI： 10.1007/s10948-019-5031-6

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Development of a Highly Sensitive Magnetic Field Detector with a Wide Frequency Range for Nondestructive Testing Using an HTS Coil with Magnetic Sensors Reviewed

Tetsuro Hirata, Yuto Goda, Kenji Sakai, Toshihiko Kiwa, Seiji Adachi, Akira Tsukamoto, Tsunehiro Hato, Keiichi Tanabe, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   29 ( 5 )   2019.8

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© 2002-2011 IEEE. To perform an early stage detection of the deterioration of steel parts used in infrastructures, a nondestructive testing (NDT) method is required, which is capable of evaluating hidden parts such as a steel deck covered with an asphalt pavement. To achieve this, a magnetic field detector should be sufficiently large to detect magnetic fields over a wide range to account for high lift-off. In addition, the detector must be capable of functioning at high frequencies for a high-speed inspection of surface cracks, and at low frequencies to compensate for the skin effect during the inspection of inner or rear side cracks. In this paper, we developed a magnetic field detector for eddy current testing in a wide frequency range by combining a high-temperature superconducting (HTS) coil made using DI-BSCCO tapes with a tunnel magnetoresistive (TMR) sensor. The TMR sensor was attached on the inside of the loop of the HTS coil to maximize the shielding characteristic. We applied the developed system to NDT, which can detect a signal from an artificial crack with a lift-off of 75 mm, which is greater than the thickness of the asphalt pavement. In addition, inner cracks that are 2.7 mm beneath the surface can be detected with a 10 Hz applied magnetic field.

DOI： 10.1109/TASC.2019.2904485

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Extraction Method of Crack Signal for Inspection of Complicated Steel Structures Using A Dual-Channel Magnetic Sensor. International journal

Minoru Hayashi, Taisuke Saito, Yoshihiro Nakamura, Kenji Sakai, Toshihiko Kiwa, Izumi Tanikura, Keiji Tsukada

Sensors (Basel, Switzerland)   19 ( 13 )   2019.7

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Conventional eddy current testing (ECT) using a pickup coil probe is widely employed for the detection of structural cracks. However, the inspection of conventional ECT for steel structures is difficult because of the magnetic noise caused by the nonuniform permeability of steel. To combat this challenge, we have developed a small magnetic sensor probe with a dual-channel tunneling magnetoresistance sensor that is capable of reducing magnetic noise. Applying this probe to a complicated component of steel structures-such as the welds joining a U-shaped rib and deck plate together-requires the reduction of signal fluctuation caused by the distance (liftoff) variations between the sensor probe and the subject. In this study, the fundamental crack signal and the liftoff signal were investigated with the dual-channel sensor. The results showed that the liftoff signals could be reduced and differentiated from the crack signals by the differential parameters of the dual-channel sensor. In addition, we proposed an extraction technique for the crack signal using the Lissajous curve of the differential parameters. The extraction technique could be applied to the inspections not only for flat plates but also for welded angles to detect cracks without the influence of the liftoff signal.

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Using Magnetic Field Gradients to Shorten the Antigen-Antibody Reaction Time for a Magnetic Immunoassay

Keiji Tsukada, Kenta Tsunashima, Katsuya Jinno, Bunta Hiramatsu, Shun Takeuchi, Kayo Fujimoto, Kenji Sakai, Toshihiko Kiwa, Mohd Mawardi Saari

IEEE Transactions on Magnetics   55 ( 7 )   2019.7

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© 1965-2012 IEEE. The measurement of biological targets using nanoparticle magnetic markers has been extensively studied for its applications in magnetic immunoassays (MIAs). Compared with the optical immunoassay method, the MIA methods have some attractive characteristics such as a wash-free process that does not need bound/free marker separation and the ability to detect biological targets in a nebulous liquid. In addition, the wash-free process is very fast. In this paper, we tried to reduce the reaction time for the antigen-antibody reaction in order to make the MIA method more attractive. The reduction in reaction time and the detection characteristic of biological targets were demonstrated using C-reactive proteins (CRPs) as biological targets for diagnosing inflammation. To shorten the reaction time, a magnetic-shaking method using the magnetic field gradient from a neodymium magnet was developed. When comparing the reaction times with and without magnetic shaking, it was found that the reaction time decreased with magnetic shaking for all CRP concentrations. Even after the magnetic-shaking treatment, the dependence of the CRP concentration on the magnetic signal was observed. The number of surface modifications per magnetic marker and the magnetic marker concentration also affected the reaction time. In order to obtain the desired measurement range based on the CRP response characteristic, it is necessary to optimize the number of magnetic markers and polymer beads used.

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Improvement of contrast of Terahertz Images of a Terahertz Chemical Microscopy using Adaptive Digital Filter

Feroz Ahmed, Tatsuki Kamiya, Yuki Maeno, Toshihiko Kiwa, Kenji Sakai, Keiji Tsukada

5th International Conference on Computer, Communication, Chemical, Materials and Electronic Engineering, IC4ME2 2019   2019.7

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© 2019 IEEE. A Terahertz Chemical Microscope has been proposed and developed for the visualization of chemical reactions in the solutions. To visualize chemical reactions with higher imaging quality and higher scanning speed, it is required to improve the contrast of the images. In this study, we applied an adaptive filter to the TCM system and evaluate the imaging quality qualitatively. The contrasts without filter and with filter are 0.33 and 0.74 respectively. This result shows that our system with the filter could improve the imaging quality without losing the scanning speed of the microscope.

DOI： 10.1109/IC4ME247184.2019.9036485

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High-sensitivity detection of metastatic breast cancer cells via terahertz chemical microscopy using aptamers Reviewed

Eman M. Hassan, Ahmed Mohamed, Maria C. DeRosa, William G. Willmore, Yuki Hanaoka, Toshihiko Kiwa, Tsuneyuki Ozaki

Sensors and Actuators, B: Chemical   287   595 - 601   2019.5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

© 2019 Elsevier B.V. We demonstrate high-sensitivity detection of metastatic breast cancer cells using terahertz (THz) chemical microscopy (TCM) with aptamers as ligands. For the aptamers, we use previously developed synthetic single stranded (ss) DNA aptamers mammaglobin B1 (MAMB1) and mammaglobin A2 (MAMA2) that bind to mammaglobin B and mammaglobin A proteins, respectively, which are overexpressed on the surface of MCF7 and MDA-MB-415 breast cancer cells. Each aptamer was immobilized on the surface of a sensing plate, and the amplitude of the THz signal was measured upon the binding of each aptamer to different number (10–106) of its target breast cancer cells. A change in the THz amplitude was observed when MAMB1 and MAMA2 bind to MCF7 and MDA-MB-415, respectively. We find that this change was linear as a function of the log number of breast cancer cells used. No change in the THz amplitude was observed when the same number of normal breast cells (MCF 10A) were used. Moreover, MAMB1 and MAMA2 did not show binding to the counter breast cancer cells, indicating high selectivity. We have demonstrated that the TCM using aptamers as ligands has a limit of detection as small as 1 breast cancer cell in 100 μL of sample. Results described here indicate that the TCM could be a powerful tool to detect metastatic breast cancer cells.

DOI： 10.1016/j.snb.2019.02.019

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Hybrid Magnetic Sensor Combined with a Tunnel Magnetoresistive Sensor and High-Temperature Superconducting Magnetic-Field-Focusing Plates Reviewed

Keiji Tsukada, Tetsuro Hirata, Yuto Goda, Kenji Sakai, Toshihiko Kiwa

IEEE Transactions on Applied Superconductivity   29 ( 3 )   2019.4

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© 2002-2011 IEEE. Magnetoresistive (MR) sensors are widely used, particularly in consumer products. However, in applications requiring extremely sensitive magnetic sensors, superconducting quantum interference devices (SQUIDs) are primarily used. In this study, we develop a hybrid magnetic sensor by combining an MR sensor with two high-temperature superconducting (HTS) plates to achieve sensitivity that lies between those of MR sensors and SQUIDs. In addition, we apply a modulation method for measuring the absolute magnetic field. A nanogranular in-gap tunnel MR sensor is installed inside the slit between the magnetic-field-focusing HTS plates, and the magnetic response is evaluated. Using the magnetic-field-focusing characteristics of the HTS plates (made from YBa2Cu3O7-δ) and the MR sensor inside the slit between the two plates, the sensitivity and noise characteristics are improved. Adjustment of parameters, such as MR sensor height from the slit, slit width of the HTS plates, and plate size allow sensitivity control depending on the application. Moreover, the absolute magnetic response and low noise in low-frequency regions are obtained through ac modulation.

DOI： 10.1109/TASC.2018.2874354

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Imaging of chemical reactions using a terahertz chemical microscope Reviewed

Toshihiko Kiwa, Tatsuki Kamiya, Taiga Morimoto, Kentaro Fujiwara, Yuki Maeno, Yuki Akiwa, Masahiro Iida, Taihei Kuroda, Kenji Sakai, Hidetoshi Nose, Masaki Kobayashi, Keiji Tsukada

Photonics   6 ( 1 )   2019

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© 2019 by the authors. This study develops a terahertz (THz) chemical microscope (TCM) that visualizes the distribution of chemical reaction on a silicon-based sensing chip. This chip, called the sensing plate, was fabricated by depositing Si thin films on a sapphire substrate and thermally oxidizing the Si film surface. The Si thin film of the sensing plate was irradiated from the substrate side by a femtosecond laser, generating THz pulses that were radiated into free space through the surface field effect of the Si thin film. The surface field responds to chemical reactions on the surface of the sensing plate, changing the amplitude of the THz pulses. This paper first demonstrates the principle and experimental setup of the TCM and performs the imaging and measurement of chemical reactions, including the reactions of bio-related materials.

DOI： 10.3390/photonics6010010

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Integrated Magnetic Sensor Probe and Excitation Wire for Nondestructive Detection of Submillimeter Defects

Keiji Tsukada, Hiroto Shobu, Yuto Goda, Takumi Kobara, Kenji Sakai, Toshihiko Kiwa, Mohd Mawardi Saari

IEEE Magnetics Letters   10   2019

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© 2010-2012 IEEE. Eddy current testing with excitation and pickup coils is widely used to detect defects in metals. The detection of submillimeter defects is difficult because of limitations on pickup coil size. We have developed an integrated magnetic probe for detecting submillimeter defects in both nonmagnetic and ferromagnetic materials. The sensor probe consists of a tunneling magnetoresistance (TMR) device and an excitation wire. This probe can apply small, localized magnetic fields to a sample that is near the TMR sensor. The direction of the field excitation is perpendicular to the sensing direction of the TMR sensor to minimize magnetic coupling between the excitation wire and the sensor. A change in the line-scanned signal was detected when measuring pits from 0.5 mm to 1.0 mm in diameter at depths of more than 0.1 mm in both steel and aluminum plates. Signal changes depended on defect size. As the frequency was increased from 1 kHz to 50 kHz, the defect signal change for the aluminum plate increased due to an increase in eddy currents. A clear defect signal for the steel plate was obtained even at a low frequency of 1 kHz because the detected signal for steel consists of a frequency-dependent eddy-current component and a magnetization component even at low frequencies.

DOI： 10.1109/LMAG.2019.2936392

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Magnetic NDE system for detection of crack in steel deck with high lift-off using secondary differential detection coil

Yuto Goda, Hiroto Shobu, Takumi Kobara, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Keiichi Tanabe, Keiji Tsukada

10th International Workshop NDT in Progress   2019

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© International Workshop NDT.All rights reserved. Recently, the aging of buildings and infrastructure facilities is becoming a social problem. In the steel structure, the nondestructive evaluation with high lift-off is required to inspect the steel material under the asphalt or concrete, such as the steel floor slabs of roads. Under the high lift-off condition, the influence of the magnetic noise and applied magnetic field should be reduced because the signal from the crack is small. In order to reduce the influence of the magnetic noise, in this study, the detection of crack signal by eddy current testing was examined using a detection coil of a differential coil. This differential coil is a secondary differential coil combining two differential coils aiming for improving the signal to noise ratio (SNR) by reducing the influence of the magnetic noise and applied magnetic field. Using this secondary differential coil, the crack with high liftoff of 80 mm was detected, and it is expected to detect the cracks in steel structures located under the asphalt or concrete.

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Design of eddy current testing probe for surface defect evaluation

M. M. Saari, N. A. Nadzri, A. M. Halil, M. Ishak, K. Sakai, T. Kiwa, K. Tsukada

International Journal of Automotive and Mechanical Engineering   16 ( 1 )   6357 - 6367   2019

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© Universiti Malaysia Pahang, Malaysia. Early detection of defects in metallic components used in infrastructure is crucial to ensure their safety and reliability. This paper presents a development of a small eddy current testing (ECT) probe for evaluation of sub-millimetre surface defects. The ECT probe is developed in a planar differential using sensitive anisotropy magnetoresistance sensors, and the signal amplification is achieved by a home-made instrumentation amplifier. The developed ECT probe is evaluated by performing phase sensitive measurement of the magnetic responses of sub-millimetre surface slits at the excitation field of 200 Hz and 10 kHz. Compared to the real component of the magnetic response, the imaginary component can be used to identify the existence and position of the slits based on the signal intensity change caused by the induced eddy current. The spatial distribution of the magnetic response measured by the ECT probe can be used to estimate the dimension of the slit. It is expected that the developed ECT probe can be utilised for assessment of sub-millimetre surface defect.

DOI： 10.15282/ijame.16.1.2019.19.0481

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Detection of lung cancer cells using a terahertz chemical microscope

Kosuke Sato, Masahiro Iida, Hirofumi Inoue, Toshihiko Kiwa, Shinichi Toyooka, Keiji Tsukada

Optics InfoBase Conference Papers   Part F146-JSAP 2019   2019

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© 2019 OSA - The Optical Society. All rights reserved. We have developed the TCM to evaluate the ration of cancer cells to normal cells for realizing the cancer genome therapy. The THz amplitude radiated from the sensing plate increased by increasing the cell population of lung cell carcinoma.

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Optimization of inclined angle magnetic sensor probe to improve detection performance of corrosion near the ground using extremely low-frequency eddy current testing

Shunki Wakabayashi, Minoru Hayashi, Taisuke Saitoh, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

10th International Workshop NDT in Progress   2019

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© International Workshop NDT.All rights reserved. As the aging of steel pipes used for sign pole is caused by the corrosion near ground, a quantitative evaluation of the corrosion location and thinning rate from the ground surface is required. Therefore, we have proposed a magnetic nondestructive testing for the steel pipes using two magnetic sensors, and it was possible to inspect the underground corrosion defects. However, in order to improve the accuracy of estimating the thinning rate and position of underground corrosion, the optimization of the inclination angle of the magnetic sensor probe and the distance between two magnetic sensors has been required. Therefore, in order to extract the signal change caused by the thinning rate of the test sample and the measurement distance, the distance dependence which is the relationship between the signal intensity and the measurement distance was measured and the measured value was normalized by the signal intensity measured at uncorroded area. As a result, the difference between the signal intensity at the uncorroded part and that near the corrosion defect could be clearly extracted. Furthermore, the rate of change of signal intensity increased by changing the tilt angle of probe and the distance between two sensors. Using the optimized magnetic sensor probe and applying the normalized distance dependence, we succeeded in the quantitative evaluation of the thinning rate and position of corrosion defects.

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Optimization of applied magnetic field methods for various shape defects by eddy current testing using magneto resistive sensor

Takumi Kobara, Yuto Goda, Hiroto Shobu, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

10th International Workshop NDT in Progress   2019

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© International Workshop NDT.All rights reserved. In this study, we investigated the optimization of applied magnetic field methods for defect detection for various shapes of defects made of magnetic and non-magnetic materials using the eddy current testing with a highly sensitive magnetic sensor. From the experiment and simulation results, it was found that the change of the magnetic field distribution caused by the eddy current increased when the sensor was placed directly above the induction coil of the wire-type method. Moreover, in the solenoid coil system, it was found that the detection sensitivity increased when the magnetic sensor was placed close to one side of the coil compared to that placed at the center. In addition, it was found that the signal change was different in the electromagnetic characteristics of the measurement sample. For the non-magnetic material, as the frequency increased, the signal to noise ratio (SNR) of the detected defect signal increased because the signal was generated from only the eddy current. On the other hand, for the magnetic material, there was an optimum frequency for detecting the defect because the signal was generated due to both the magnetization and the eddy current. As a results, the optimum applying method of magnetic field for the eddy current testing using magnetic sensor was clarified.

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The nondestructive evaluation of penetration of the cosmetic liquid into the pig skin

Sota Sueda, Taihei Kuroda, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Optics InfoBase Conference Papers   Part F146-JSAP 2019   2019

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Measurement of ion concentration in the solution without reference electrodes using a terahertz chemical microscopy

Atsuya Mahana, Yuki Maeno, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Optics InfoBase Conference Papers   Part F146-JSAP 2019   2019

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© 2019 OSA - The Optical Society. All rights reserved. A terahertz chemical microscopy (TCM) has been proposed and developed for measuring pH and the ion concentration with the multiple and small volume of solutions simultaneously. By fabricating multiple wells on the sensing plate to measure standard solutions, quantitative measurement of ions could be possible without any reference electrodes.

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Magnetic detection of steel corrosion at a buried position near the ground level using a magnetic resistance sensor Reviewed

Keiji Tsukada, Takuya Tomioka, Shunki Wakabayashi, Kenji Sakai, Toshihiko Kiwa

IEEE Transactions on Magnetics   54 ( 11 )   2018.11

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© 1965-2012 IEEE. Corrosion of steel structures, such as lighting and road marker poles, located in close proximity to or buried within the ground have become a social problem. Steel corrosion has been observed to occur rather easily near the ground level. However, corrosion detection in parts of steel structures buried within the ground is very difficult. To address this concern, a magnetic resistance testing system for detecting corrosion in buried steel structures has been developed using a tilted magnetic sensor probe, and it is based on our independently developed extremely low-frequency eddy-current testing methodology. The magnetic sensor probe comprises an anisotropic magnetic resistance sensor, induction coil, and small cancellation coil. The applied magnetic field was operated at extremely low frequencies between 1 and 100 Hz, and the magnetic spectrum, which was traced using the real and imaginary parts of the detected magnetic signal at each frequency, was analyzed for estimating changes in steel thickness. Test samples comprising 4 mm thick stainless steel plates with a partial thinning zone varying in depth between 0.5 and 3.0 mm were used during measurements. Changes in thickness were detected at locations other than the thinning zone by using the differential-magnetic-intensity-subtracted magnetic vector of frequency 1 Hz from that of frequency 20 Hz detected by the tilted magnetic sensor probe. Moreover, the depth of corrosion and its corresponding location beneath the ground level were estimated via measuring techniques involving the use of magnetic sensor probes in the separated position or at different tilt angles in the same position.

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Evaluation of Li-ion battery using a Terahertz Chemical Microscope Reviewed

Yuki Akiwa, Kentarou Fujiwara, Yumi Yoshikawa, Takashi Teranishi, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2018-September   2018.10

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© 2018 IEEE. We measured the terahertz wave intensity of the active material surface using TCM as a method to evaluate lithium ion batteries. We made a battery with a sensing plate attached to measure with TCM. As a result, changes in the terahertz wave intensity due to charging and discharging of the battery could be measured. This result indicates that the extraction and insertion of lithium in the active material can be measured by TCM in the future.

DOI： 10.1109/IRMMW-THz.2018.8509878

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Detection of Ions in Solutions with Sub-Micro Liter Volumes Using a Terahertz Chemical Microscope

Y. Maeno, T. Kamiya, T. Kiwa, K. Sakai, K. Tsukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2018-September   2018.10

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© 2018 IEEE. A terahertz chemical microscope (TCM) has been proposed and developed for measuring the small volume of the ion concentrations in solutions. By fabricating the small solution wells and the ion selective membranes on the sensing plate, the concentration of the sodium ions in the solution of 450 nL could be measured.

DOI： 10.1109/IRMMW-THz.2018.8510464

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Concentration Dependence of IgG Immobilized on a Sensing Plate for Higher Sensitivity of a Terahertz Chemical Microscope

M. Iida, T. Kamiya, K. Sakai, T. Kiwa, K. Tukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2018-September   2018.10

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© 2018 IEEE. We have developed a terahertz chemical microscope for measuring immune reactions without any label. Here, to evaluate the relation between the concentration of IgG immobilized on the sensing plate and the sensitivity of the system, the concentration dependence of the IgG was evaluated.

DOI： 10.1109/IRMMW-THz.2018.8509884

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A sensitive AC magnetometer using a resonant excitation coil for magnetic fluid characterization in nonlinear magnetization region Reviewed

Mohd Mawardi Saari, Nazatul Sharreena Suhaimi, Nurul Akmal Che Lah, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

2018 IEEE International Magnetic Conference, INTERMAG 2018   2018.10

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© 2018 IEEE. In order to tailor the magnetic nanoparticles (MNPs) properties for intended applications, it is crucial to unravelling their fundamental dynamics with respect to excitation magnetic field. In this work, we report on the development of a sensitive AC magnetometer using a resonant excitation coil for this purpose. The excitation coil fabricated from a Litz wire is connected to a capacitor network to reduce the impedance of the circuit efficiently. The high efficiency showed by the excitation coil enables investigation of MNP's dynamics in the nonlinear magnetization region. We demonstrate the sensitivity of the developed system by measuring the harmonics distribution of multi-core iron oxide nanoparticles suspended in solutions with the iron concentration down to 300 ng/ml. We experimentally show that the first harmonic component is not entirely 'transparent' to the diamagnetic background of the carrier liquid compared to the higher harmonics. We also demonstrate the complex magnetization measurement of the iron oxide nanoparticles in solution and immobilized states from 3 Hz to 18 kHz. A highly sensitive exploration of MNPs' dynamics can be expected using the developed AC magnetometer.

DOI： 10.1109/INTMAG.2018.8508784

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Sensitivity Improvement of Sample Rotation Measurement Method in HTS-SQUID Magnetometer for Diamagnetic Materials Reviewed

Yuta Nakamura, Ryota Isshiki, Shun Takeuchi, Tetsuro Hirata, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   28 ( 4 )   2018.6

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© 2002-2011 IEEE. Measuring extremely low magnetic signals of diamagnetic materials such as water and ethanol with high sensitivity is important in various fields. Ethanol is widely used as a solvent in areas such as chemical industry and drug discovery; therefore, it is important to measure its concentration with high sensitivity. We have already reported a hybrid-type magnetometer using a high temperature superconductor superconducting quantum interference device (HTS-SQUID), which can measure and evaluate magnetic characteristics by vibrating and rotating a sample. However, the signal-to-noise ratio (SNR) of the system needs to be improved as magnetic signals from diamagnetism in water and ethanol are extremely low in magnitude. In this study, digital frequency filters were applied to the signals measured by the HTS-SQUID magnetometer with a rotating sample container in order to improve the SNR of the system, and then the magnetic properties of ethanol and water were studied. As a result, the SNR of the system improved about twice the level obtained by conventional signal processing method.

DOI： 10.1109/TASC.2018.2810088

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Evaluation of the Magnetization Properties of Magnetic Nanoparticles in Serum Using HTS-SQUID Reviewed

Ryota Isshiki, Yuta Nakamura, Shun Takeuchi, Tetsuro Hirata, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   28 ( 4 )   2018.6

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© 2018 IEEE. The magnetization properties of magnetic nanoparticles (MNPs) changed by the action of the buffer and serum solutions with different viscosities were analyzed using dc and ac magnetometers that utilized high-temperature superconductivity-superconducting quantum interference devices. The magnetization properties of MNPs in different solutions with different viscosities were measured using a dc magnetometer via vibrating the sample under a dc magnetic field. The harmonic signal characteristics of the MNPs in different solutions were measured in a low-frequency magnetic field. In addition, the dynamic changes in the magnetic characteristics of MNPs in different solutions were measured using an ac magnetometer with a high frequency. The results corresponding to the low- and high-frequency fields showed that both viscosity of the solvent and the interactions between the MNPs and the solvent are important influencing factors in immunoassays using MNPs.

DOI： 10.1109/TASC.2018.2795619

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Analysis of AC Impedance in Localized Region Using Magnetic Field Distribution Measured by HTS-SQUID Reviewed

Kenji Sakai, Tsubasa Kizu, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   28 ( 4 )   2018.6

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© 2002-2011 IEEE. Estimation of ac impedance in a localized region was investigated by measuring the magnetic field from an electrical current induced by applying an ac voltage to a sample. For this measurement, a high-temperature-superconductor superconducting quantum interference device (HTS-SQUID) was used to detect a small magnetic field from a sample. To clarify the detection of ac impedance in a localized region, a dye-sensitized solar cell (DSSC) with a positive electrode consisting of two catalysis materials was prepared. Although the I-V characteristic and electrochemical impedance spectroscopy (EIS) of the solar cell with two catalysis materials were different from those of the solar cell with a one catalysis material, it was difficult to evaluate the ac impedance of the localized region. The magnetic field from the solar cell with two catalysis materials depended on the measurement position at which the catalysis material located under HTS-SQUID was different. This difference was correlated to the ac impedance change predicted by the measured EIS. Moreover, the mapping obtained by magnetic field distribution near the interface of two catalysis materials showed a different magnetic field intensity, which was correlated to the position of each catalysis material. These results indicate that the analysis of the localized ac impedance is possible using the magnetic field distribution generated from a sample.

DOI： 10.1109/TASC.2018.2796609

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pH measurements in 16-nL-volume solutions using terahertz chemical microscopy. Reviewed International journal

Toshihiko Kiwa, Tatsuki Kamiya, Taiga Morimoto, Kenji Sakai, Keiji Tsukada

Optics express   26 ( 7 )   8232 - 8238   2018.4

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Terahertz chemical microscopy has been developed for measuring the pH of a solution using only a small volume. The microsolution wells were fabricated on the surface of the sensing plate using a conventional photolithograph technique. Because the pH value can be calculated from the amplitude of a terahertz wave directly radiated from a sensing plate by a femtosecond laser irradiation, this method does not require any reference electrode in the solution. Thus, pH measurement can be achieved with a volume as small as 16 nL.

DOI： 10.1364/OE.26.008232

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Harmonics distribution of iron oxide nanoparticles solutions under diamagnetic background Reviewed

Mohd Mawardi Saari, Nurul Akmal Che Lah, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Magnetism and Magnetic Materials   452   145 - 152   2018.4

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© 2017 Elsevier B.V. The static and dynamic magnetizations of low concentrated multi-core iron oxide nanoparticles solutions were investigated by a specially developed high-Tc Superconducting Quantum Interference Device (SQUID) magnetometer. The size distribution of iron oxide cores was determined from static magnetization curves concerning different concentrations. The simulated harmonics distribution was compared to the experimental results. Effect of the diamagnetic background from carrier liquid to harmonics distribution was investigated with respect to different intensity and position of peaks in the magnetic moment distribution using a numerical simulation. It was found that the diamagnetic background from carrier liquid of iron oxide nanoparticles affected the harmonics distribution as their concentration decreased and depending on their magnetic moment distribution. The first harmonic component was susceptible to the diamagnetic contribution of carrier liquid when the concentration was lower than 24 μg/ml. The second and third harmonics were affected when the peak position of magnetic moment distribution was smaller than m = 10−19 Am2 and the concentration was 10 ng/ml. A highly sensitive detection up to sub-nanogram of iron oxide nanoparticles in solutions can be achieved by utilizing second and third harmonic components.

DOI： 10.1016/j.jmmm.2017.12.054

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Development of a resonant excitation coil of AC magnetometer for evaluation of magnetic fluid

Mohd Mawardi Saari, Nazatul Sharreena Suhaimi, Saifudin Razali, Nurul Akmal Che Lah, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Telecommunication, Electronic and Computer Engineering   10 ( 1-2 )   127 - 130   2018.1

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© 2018 Universiti Teknikal Malaysia Melaka. All rights reserved. A high-homogeneity excitation coil with a resonant circuit for AC magnetometer is developed. A solenoid coil is designed to produce a high-homogeneity and strong excitation field using a resonant frequency method. The solenoid coil is fabricated with a Litz wire to suppress the increase of AC resistance due to the skin and proximity effects in the high-frequency region. The Litz wire is composed of 60 strands of copper wires with 0.1-mm diameter. The resonant frequency method is applied to cancel the reactance component by connecting the excitation coil with a capacitor in a series configuration. To enable excitation of the magnetic field at multiple frequencies, a resonant circuit consists of multiple values of resonant capacitors is constructed. The fabricated excitation coil showed a high homogeneity of the magnetic field and was able to maintain a constant resonant current up to 32.5 kHz.

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Small Eddy Current Testing Sensor Probe Using a Tunneling Magnetoresistance Sensor to Detect Cracks in Steel Structures Reviewed

Keiji Tsukada, Minoru Hayashi, Yoshihiro Nakamura, Kenji Sakai, Toshihiko Kiwa

IEEE Transactions on Magnetics   54 ( 11 )   2018

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© 1965-2012 IEEE. An eddy current test (ECT) is a common nondestructive test to detect flaws in metal structures. Many ECTs use both a detection coil and an induction coil. The application of this method to ferromagnetic materials can be challenging because the applied magnetic field is composed of not only the eddy current but also the magnetization signal. Therefore, we developed two types of miniaturized ECT probes, namely, single-and dual-channel tunneling magnetoresistance (TMR) probes, by using a TMR sensor instead of a detection coil. To evaluate the performance of crack detection in steel with regard to the length, width, and depth of cracks, the sensor probe was line-scanned above the crack position. The output signal was detected using a lock-in amplifier and analyzed using the real and imaginary components of a magnetic vector. The detected signal was then divided into the magnetization and eddy current components. The dual TMR sensor probe installed inside the induction coil could yield a stable crack signal without the influence of magnetization fluctuation. The line-scanned differential signal intensity and phase show a signal change with a high signal-to-noise ratio at the crack position. These signals depend on the width and length of the crack. A 2-D scanning could provide a magnetic map corresponding to the crack shape.

DOI： 10.1109/TMAG.2018.2845864

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Evaluation of penetration of cosmetic liquid with Terahertz time-of-flight method

Taiga Morimoto, Taihei Kuroda, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Optics InfoBase Conference Papers   Part F113-CLEOPR 2018   2018

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© OSA 2018 A terahertz time-of-flight method has been developed to evaluate penetration of cosmetic liquid. By using a face mask as the reservoir of the cosmetic liquid, the evaluation from the horny layers could be realized.

DOI： 10.1364/cleopr.2018.tu3c.5

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Characterizing of corrosion backside of steel plates using extremely low-frequency eddy current testing with multiple-frequency magnetic-field exposure

Tsuyoshi Goda, Yuta Haga, Takuya Tomioka, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Studies in Applied Electromagnetics and Mechanics   43   130 - 135   2018

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© 2018 The authors and IOS Press. In recent years, aging and deterioration of social infrastructure has become a major problem. A non-destructive testing technique for early detection of degradation (such as internal corrosion) is required to extend the lifetime of these structures. Currently, there are various methods used for inspection. Among these, non-destructive testing using magnetic fields is widely used due to advantages such as ease of use and high speed. However, magnetic inspection is generally employed only for inspection of the surface and subsurface, since it is difficult to inspect internal corrosion using this technique. Therefore, we have developed a device for detecting thinning of steel plates due to corrosion using multiple extremely-low frequencies and a high-sensitivity magnetic sensor. However, it is necessary to sweep multiple frequencies to obtain a frequency spectrum, and this is very timeconsuming, especially in extremely low-frequency ranges. In this study, we have developed an analysis method based on a multiple-frequency applied magnetic field and FFT (fast Fourier transform) analysis of the detection signal. Thus, we have successfully reduced the measurement time while maintaining high detection accuracy.

DOI： 10.3233/978-1-61499-836-5-130

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Detection Method Using a Dual-channel Magnetic Sensor for Steel Cracks in Complicated Structures

Minoru Hayashi, Yoshihiro Nakamura, Kenji Sakai, Toshihiko Kiwa, Izumi Tanikura, Keiji Tsukada

Proceedings of the 7th Asia-Pacific Workshop on Structural Health Monitoring, APWSHM 2018   580 - 586   2018

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© APWSHM 2018. All rights reserved. Conventional eddy current testing (ECT) using a pickup coil is widely employed for detecting cracks. However, it is sometimes difficult to apply conventional ECT to steel structures because of the magnetic noise caused by the non-uniform permeability of steel. To combat this challenge, we developed a small magnetic sensor probe with dual-channel tunnelling magnetic resistance capable of reducing magnetic noise. To apply the developed magnetic sensor probe to a complicated component of a steel structure, such as the welds joining the U-rib and deck plate, signal fluctuations caused by the lift-off variations between the sensor probe and the subject during magnetic sensor probing must be resolved. Therefore, we developed a method to distinguish between the signal changes caused by lift-off variations and cracks. The intensity and phase of the subtracted signal were used to develop traces of differential parameters obtained by scanning the magnetic probe. A visualization technique using only the traces of differential parameters, i.e. the Lissajous curve of X-Y processing, was applied not only to the cracks of the flat steel plate but also to the cracks in welded angles. The developed Lissajous curve emphasized the crack signals, which allowed clear differences between the signal change caused by the lift-off variations and cracks to be observed.

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Thickness measurements using extremely low frequency eddy current testing via TMR sensors operated with AC modulation

Yatsuse Majima, Yoshihiro Nakamura, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Studies in Applied Electromagnetics and Mechanics   43   199 - 204   2018

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© 2018 The authors and IOS Press. Conventionally, eddy current testing (ECT) has been used for the surface crack detection. However, the detection of underside and internal corrosion was difficult using this technique. Therefore, we developed an underside and internal corrosion detection technique based on extremely low frequency ECT (ELECT). To use the TMR sensor for ELECT, a TMR sensor operated with AC modulation was applied as a magnetic sensor. Then, we developed the ELECT system using a TMR sensor operated with AC modulation, and succeeded in measuring the thickness of thick steel plate.

DOI： 10.3233/978-1-61499-836-5-199

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Improvement in the detection performance of extremely low-frequency eddy current testing for application in underground steel corrosion detection

Shunki Wakabayashi, Takuya Tomioka, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Proceedings of the 7th Asia-Pacific Workshop on Structural Health Monitoring, APWSHM 2018   512 - 518   2018

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© APWSHM 2018. All rights reserved. The corrosion of steel structures, such as light and road sign poles, often occurs near the ground due to rainwater. The subsequent collapse of the corresponding steel structure can cause traffic accidents and potentially danger people. Therefore, a highly accurate and easy nondestructive inspection technique is required to detect corrosion near the ground, especially in hidden locations. Recently, we reported a novel inspection method using extremely low-frequency eddy current testing (ELECT) to detect the reduced steel thickness that was caused by corrosion. Wide magnetic-field exposure was achieved underground using a tilted magnetic sensor probe. Further, the fundamental detection performance and signal analysis of the test samples were also reported. In this study, we attempted to improve the detection performance and applied the measurement to actual steel structures as a field test. The ELECT system to detect corrosion near the ground comprised a magnetic sensor probe, a sensor circuit, a multiple-frequency alternative current (AC) current source for the induction coil, a lock-in detector, and a personal computer. The magnetic probe consisted of two anisotropic magnetic resistance sensors, induction coils to generate eddy currents in the steel structures, and the cancellation coil to reduce the directly coupled magnetic field exposure. The magnetic spectrum curve, which can be used to trace the obtained magnetic field vectors (intensity and phase), was acquired by multiple-frequency exposure. The reduction in steel thickness was further estimated based on the changes in magnetic curve. The optimization of certain parameters, such as the exposure coil shape and lift-off between the sensor probe and the steel, led to improvements in the magnetic curve, which enabled sensitive detection; further, 1-mm thinning was successfully detected at a depth of 60 mm. Furthermore, the results obtained by the ELECT system at the ground surface were in good agreement with the results of the thickness measurements that were directly obtained from the structure after digging into the ground.

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Evaluation of hardened and non- ardened regions using eddy current testing

Kenji Sakai, Takahiro Ito, Toshihiko Kiwa, Keiji Tsukada

Studies in Applied Electromagnetics and Mechanics   43   1 - 8   2018

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© 2018 The authors and IOS Press. A steel plate having hardened and non-hardened regions in one plate is promising material in automobile field owing to its high performance. This steel plate has to be evaluated whether the non-hardened region was prepared properly at the desired position with desired hardness. However, the conventional evaluation method of hardness measurement is destructive testing and requires a long inspection time. Therefore, a reliable and fast nondestructive inspection method is required. In this study, the hardened and non-hardened regions were evaluated using an eddy current testing (ECT) to distinguish each region. The measured resistivity and permeability at each region were different and these differences were found to be caused by the crystal structure change of heat treatment. Therefore, the magnetic response between the hardened and nonhardened regions was different and this difference was correlated with the hardness of each region. These results indicate that the hardened and non-hardened regions can be distinguished using ECT.

DOI： 10.3233/978-1-61499-836-5-1

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Development of in situ methods for battery using a THz chemical microscope

Kentaro Fujiwara, Yuki Akiwa, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Optics InfoBase Conference Papers   Part F113-CLEOPR 2018   2018

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© OSA 2018 It is important to measure the special deviation of electrochemical reactions on electrodes to improve the performance of batteries. Here, electrochemical measurement using THz chemical microscope with a sealed container was applied for measurements.

DOI： 10.1364/cleopr.2018.tu3c.6

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Immune assay using a micro-flow channels detected by a terahertz chemical microscopy

Tatsuki Kamiya, Masahiro Iida, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Optics InfoBase Conference Papers   Part F113-CLEOPR 2018   2018

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© OSA 2018 We have developed a terahertz chemical microscopy (TCM) to visualize various types of chemical reactions. Here, a micro-flow channels were fabricated on a sensing plate, and measured time evolution of immune reactions using the TCM.

DOI： 10.1364/cleopr.2018.tu3c.3

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Evaluation of penetration of cosmetic liquids using terahertz time of flight method

T. Kuroda, T. Morimoto, K. Sakai, T. Kiwa, K. Tsukada

2018 43RD INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ)   2018

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The terahertz time-of-flight method was applied to evaluate the the penetration speed and the depth of the skin lotion into the skin. The result suggests that the terahertz time-of-flight method is one of useful option in this field.

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Application of a HTS Coil with a Magnetic Sensor to Nondestructive Testing Using a Low-Frequency Magnetic Field Reviewed

Yasuaki Matsunaga, Ryota Isshiki, Yuta Nakamura, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   27 ( 4 )   2017.6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

© 2016 IEEE. Detecting corrosion at an early stage on the backside of a thick steel plate using a magnetic field is difficult because of the high permeability of steel. Therefore, we used a low-frequency magnetic field to enable the penetration of magnetic flux deep into the steel plate. According to Faraday's law, to achieve a sufficiently intense signal at low frequencies, the number of turns of a normal conducting coil must be increased. However, a high-temperature superconducting (HTS) coil has a very low resistance; thus, the shielding current of a HTS coil can flow under magnetic fields with a wide-frequency range. Although HTS coils exhibit good shielding characteristics at low frequencies, their voltage signals are very weak. To solve this problem, a magnetic sensor was used to detect the shielding current of a HTS coil. The detection unit included the HTS coil, and the magnetic sensor was optimized; moreover, the possibility of operating the magnetic sensor at the liquid nitrogen temperature (77 K) was investigated. As a demonstration of nondestructive testing using the magnetic response of the HTS coil and magnetic sensor, we measured the change in the thickness of a steel plate in which corrosion was assumed to have occurred. Consequently, we obtained a good response even with a low-frequency magnetic field when using a HTS coil with a few turns. In the thickness measurements of steel plates, thicknesses ranging from 6 to 19 mm were obtained in the frequency range of 1-5 Hz.

DOI： 10.1109/TASC.2016.2631420

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Detecting internal defects of a steel plate by using low-frequency magnetic flux leakage method Reviewed

Nannan Song, Yuta Haga, Tsuyoshi Goda, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

SAS 2017 - 2017 IEEE Sensors Applications Symposium, Proceedings   MAG-16 ( 119-132.134 )   2017.4

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© 2017 IEEE. Steel is an important material in modern society. It is widely used in our lives, such as in buildings, bridges, and airplanes. We previously reported an analysis method for examining the internal defects of metal structures with eddy current testing (ECT) over a wide range of frequencies. However, internal defects in steel plates are difficult to detect using ECT. In this paper, we present a low-frequency magnetic flux leakage (MFL) method for the nondestructive evaluation of internal defects in steel structures, and an analysis and imaging method that uses the phase of a magnetic field to examine internal defects. By analyzing the phase change in the detected signal, the internal defects can be detected with no magnetic fluctuation. The phase map of the measured magnetic field exhibits good correlation with the simulation results. The two-dimensional magnetic phase map can be used to visualize the internal defects. This new method has been validated through both experiment and simulation.

DOI： 10.1109/SAS.2017.7894069

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Novel terahertz measurements systems born in Okayama

Toshihiko Kiwa

Journal of the Institute of Electronics, Information and Communication Engineers   99 ( 10 )   975 - 979   2016.10

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Simultaneously detection two types of ions using THz chemical microscopy Reviewed

Kosuke Akimune, Yuki Okawa, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

2015 11th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2015   3   2016.1

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

© 2015 IEEE. THz chemical microscopy has been proposed and developed to detect ions in water solutions. In this work, the change in the amplitude of THz radiation was measured when ion solutions was dropped on detection plate.

DOI： 10.1109/CLEOPR.2015.7376395

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A terahertz technology for label-free immune assay Reviewed

Toshihiko Kiwa, Masahiro Ogawa, Kousuke Akimune, Hiroyuki Nino, Kenji Sakai, Keiji Tsukada

2015 11th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2015   3   2016.1

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© 2015 IEEE. This paper reviews recent works of label-free immune assay using terahertz technologies, which includes a terahertz chemical microscopy. Experimental results of label-free detection of lectin-suger chain reactions were also presented.

DOI： 10.1109/CLEOPR.2015.7376392

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pH Measurements Of nano-liter Solutions Using THz Technology Reviewed

Y. Zhou, K. Akimune, K. Hamada, K. Sakai, T. Kiwa, K. Tsukada

SENSORS AND ELECTRONIC INSTRUMENTATION ADVANCES (SEIA)   60 - 61   2016

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INT FREQUENCY SENSOR ASSOC-IFSA  

A terahertz chemical microscopy (TCM) has been proposed and developed to visualize the electric potential changes of water solution on the semiconductor-based plate named 'sensing plate'. The TCM detects the change in the amplitude of THz waves from the sensing plate, which can be related to the electric potential of the water solutions on the sensing plate. Since the top surface of the sensing plate was made from the SiO2, the electric potential at the surface of the sensing plate could be change by changing the pH values of the solutions on the sensing plate. In order to detect the small amount of water solutions, micro-wells made of UV curable resin were patterned on the surface of the sensing plate with diameters range between 50 mu m to 500 mu m. Thus the solution of 16-nL were measured, which indicated that the pH measurements of nano-litter solutions could be possible using TCM.

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Terahertz-Time-of-Flight Method for Evaluating Cosmetic Samples Penetrating into Skin Samples Reviewed

T. Arisawa, T. Morimoto, K. Sakai, T. Kiwa, K. Tsukada

SENSORS AND ELECTRONIC INSTRUMENTATION ADVANCES (SEIA)   117 - 119   2016

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A terahertz(THz)-time-of-flight(TOF) method was carried out for in-vitro measurements of the penetration depth of cosmetic liquid into skin samples. In our group, a sensing plate, which can generate terahertz pulses, has been developed. By irradiating the back side of the sensing plate using a femto-second laser pulses, the THz pulses with the pulse width of approximately 1 ps were radiated into a free space. When the artificial skin samples were put on the sensing plate, the generated THz pulses travel in the skin samples and are reflected at the boundary between the regions where the cosmetic liquid exists and does not exist. Since traveling time of the THz pulses are generally proportional to the traveling path, the distance between the boundary and the sensing plate can be estimated by evaluating the traveling time of the THz pulses. Here, as demonstration of the developed method, the penetration of liquid into the artificial dermis made from collagen were evaluated.

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Application to Non-destructive Evaluation of Gas Barrier Films Using a High-speed Terahertz Time-domain Spectroscopy Reviewed

Masaya Inamo, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

2016 PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM (PIERS)   3921 - 3921   2016

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Development of Terahertz Chemical Microscope for Detecting Small Molecules Reviewed

Takuya Kuwana, Yuki Hanaoka, Toshihiko Kiwa, Kenji Sakai, Keiji Tsukada

2016 PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM (PIERS)   3927 - 3927   2016

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Combinatorial Sensing of Catalytic Materials Using Terahertz Chemical Microscope Reviewed

Yuji Hino, Yuki Kawakami, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

SENSORS AND ELECTRONIC INSTRUMENTATION ADVANCES (SEIA)   104 - 106   2016

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Terahertz chemical microscope (TCM) has been developed to visualize the electrical and/ or chemical potential on the 'sensing plate' as the distribution of the amplitude of THz pulses radiated from the sensing plate. In this study, the combinatorial search of membrane materials using TCM was proposed and evaluation of catalytic reactions of Pt thin film was demonstrated. Pt thin films with the thickness of 4 nm, 7 nm, 10 nm and 15 nm were fabricated on the same sensing plate. Each Pt thin film on the sensing plate was exposed to the dry air (80 % nitrogen gas and 20 % oxygen gas) and hydrogen gas (1 %) and air every three minutes, independently. The amplitudes shifts of radiated THz pulses could be related to the thickness of Pt thin films on the sensing plate. This result suggests that TCM is one of useful option for the combinatorial sensing of catalytic materials.

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Automatic Scanning System for Back-Side Defect of Steel Structure Using Magnetic Flux Leakage Method Reviewed

Kenji Sakai, Koji Morita, Yuta Haga, Toshihiko Kiwa, Katsumi Inoue, Keiji Tsukada

IEEE Transactions on Magnetics   51 ( 11 )   2015.11

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© 1965-2012 IEEE. An automatic nondestructive evaluation system using the magnetic-flux-leakage method was developed for detecting the back-side defects of large structures in order to realize fast detection in a wide measurement area. A magnetic field was applied to an object using a ferrite yoke with an induction coil, and the leaked magnetic flux from the object was detected by a magnetoresistive sensor. This measurement probe was fixed on an automatic scanning system. The developed automatic scanning system detected magnetic signal changes corresponding to the back-side defects of the steel plates. To demonstrate the effectiveness of the developed system, we measured the steel plate of a cargo crane, which was corroded on the back side. We found that the detected magnetic signal changed markedly in the area with corrosion, whereas only a slight magnetic signal change was detected in the area without corrosion. Therefore, the developed system is useful for detecting the back-side defects in a wide area, and can be used for screening tests.

DOI： 10.1109/TMAG.2015.2453211

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Development of a planar type ion sensor for urine testing Reviewed

K. Sakai, T. Yamamoto, R. Sugai, T. Kiwa, K. Tsukada

Sensor Letters   13 ( 8 )   706 - 710   2015.8

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Copyright © 2015 American Scientific Publishers All rights reserved. A new planar-type ion sensor with an Ag/AgCl electrode without a standard solution and liquid junction was proposed for urine testing. The proposed sensor integrates a reference electrode onto a single chip, and thus, it is possible to manufacture a compact planar-type ion sensor. The potential change of the developed sensor is proportional to the Na+ and K+ concentration. Although the Ag/AgCl electrode without a standard solution and liquid junction reacted to Cl-, AC impedance analysis was used to compensate the effect of Cl-on the potential change. Therefore, the proposed planar-type ion sensor can be used for routine urine testing because the proposed sensor is low cost, disposable, and also has a simple structure.

DOI： 10.1166/sl.2015.3475

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Effect of diamagnetic contribution of water on harmonics distribution in a dilute solution of iron oxide nanoparticles measured using high-T<inf>c</inf> SQUID magnetometer Reviewed

Mohd Mawardi Saari, Yuya Tsukamoto, Toki Kusaka, Yuichi Ishihara, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Magnetism and Magnetic Materials   394   260 - 265   2015.7

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© 2015 Elsevier B.V. All rights reserved. The magnetization curve of iron oxide nanoparticles in low-concentration solutions was investigated by a highly sensitive high-Tc superconducting quantum interference device (SQUID) magnetometer. The diamagnetic contribution of water that was used as the carrier liquid was observed in the measured magnetization curves in the high magnetic field region over 100 mT. The effect of the diamagnetic contribution of water on the generation of harmonics during the application of AC and DC magnetic fields was simulated on the basis of measured magnetization curves. Although the diamagnetic effect depends on concentration, a linear relation was observed between the detected harmonics and concentration in the simulated and measured results. The simulation results suggested that improvement could be expected in harmonics generation because of the diamagnetic effect when the iron concentration was lower than 72 μg/ml. The use of second harmonics with an appropriate bias of the DC magnetic field could be utilized for realization of a fast and highly sensitive detection of magnetic nanoparticles in a low-concentration solution.

DOI： 10.1016/j.jmmm.2015.06.090

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Ion transportation of electrolytes in a flow channel mapped by an HTS SQUID scanning system Reviewed

Toshihiko Kiwa, Kohei Tanaka, Shohei Kasuya, Kenji Sakai, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   25 ( 3 )   2015.6

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© 2014 IEEE. In this paper, we propose and develop a device for visualizing the magnetic field produced by ion transportation in electrolyte cells. Using 0.5 mM potassium ferricyanide (K3[Fe(CN)6]) dissolved in 0.5 M sodium sulfate (Na2SO4) as the electrolyte, the magnetic distribution was obtained using high-TC SQUID scanning performed by a planar gradiometer located above the electrolyte cell across the surface. The difference in the ion transportation path in the electrolyte cells is discussed with regard to flow channels fabricated in the electrolyte cells.

DOI： 10.1109/TASC.2014.2382656

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Moisture content evaluation using improved high-tc squid-based rotating-sample magnetometer Reviewed

Kenji Sakai, Naohiro Okamoto, Yuuta Watanabe, Mohd Mawardi Saari, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   25 ( 3 )   2015.6

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© 2002-2011 IEEE. Moisture content evaluated by magnetic signal change measured by rotating-sample magnetometer using higherature superconductor superconducting quantum interference device (HTS-SQUID) was investigated. To realize highly sensitive measurement of moisture content, an improvement in signal-to-noise (S/N) ratio of the previously developed magnetometer was examined. To increase the S/N ratio, the sample case with short width along the sample's movement direction was employed. By reducing the sample case width, the obtained magnetic signal intensity increased, and the frequency component of magnetic signal shifted toward high frequencies, leading to the low magnetic field noise range measurements. Using the improved magnetometer, the moisture content of silica gel was measured, and the magnetic signal intensity increased as the amount of water in the silica gel increased. Therefore, we propose a high-sensitivity, noncontact, and nondestructive method for moisture content evaluation using rotating-sample magnetometer.

DOI： 10.1109/TASC.2014.2363353

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Optimization of an AC/DC High- T<inf>c</inf> SQUID magnetometer detection unit for evaluation of magnetic nanoparticles in solution Reviewed

Mohd Mawardi Saari, Yuichi Ishihara, Yuya Tsukamoto, Toki Kusaka, Koji Morita, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity   25 ( 3 )   2015.6

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© 2002-2011 IEEE. We have optimized the detection unit of a previously developed AC/DC magnetometer that employs a high critical temperature superconducting quantum interference device (high- Tc SQUID). Optimization involves improvement of the usable dynamic range of the high- Tc SQUID system during excitation with an AC magnetic field using a tuned compensation coil and an increase in the DC magnetic field resolution using a secondary excitation coil. The compensation coil technique had resulted in a single and compact detection coil using one SQUID for both AC and DC magnetization measurement functions with improved sensitivity in AC measurements. The sensitivity of the improved system is demonstrated by measuring the magnetization curve and harmonics distribution of low-concentration iron oxide nanoparticles solutions. Highly sensitive evaluation of magnetic nanoparticles in solutions can be expected with the developed system.

DOI： 10.1109/TASC.2014.2363633

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Characterization of the magnetic moment distribution in low-concentration solutions of iron oxide nanoparticles by a high- T <inf>c</inf> superconducting quantum interference device magnetometer Reviewed

M. M. Saari, K. Sakai, T. Kiwa, T. Sasayama, T. Yoshida, K. Tsukada

Journal of Applied Physics   117 ( 17 )   2015.5

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© 2015 AIP Publishing LLC. We developed a highly sensitive AC/DC magnetometer using a high-temperature superconductor superconducting quantum interference device for the evaluation of magnetic nanoparticles in solutions. Using the developed system, we investigated the distribution of magnetic moments of iron oxide multi-core particles of 100 nm at various iron concentrations that are lower than 96 μg/ml by analyzing the measured magnetization curves. Singular value decomposition and non-regularized non-negative least-squares methods were used during the reconstruction of the distribution. Similar distributions were obtained for all concentrations, and the iron concentration could be determined from the measured magnetization curves. The measured harmonics upon the excitation of AC and DC magnetic fields curves agreed well with the harmonics simulated based on the reconstructed magnetization curves, implying that the magnetization curves of magnetic nanoparticles were successfully obtained as we will show in the article. We compared the magnetization curves between multi-core particles of 100 nm and 130 nm, composed of 12-nm iron oxide nanoparticles. A distinctive magnetic property between the 100 nm and 130 nm particles in low-concentration solutions was successfully characterized. The distribution characteristic of magnetic moments suggests that the net magnetic moment in a multi-core particle is affected by the size of the magnetic cores and their degree of aggregation. Exploration of magnetic properties with high sensitivity can be expected using the developed system.

DOI： 10.1063/1.4919043

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Time of flight measurements of polymer films by a terahertz chemical microscopy

T. Arisawa, H. Nino, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers   Part F132-JSAP 2019   2015

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Ion sensing for nano liter level solution by a terahertz chemical microscopy

Y. Zhou, K. Akimune, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers   Part F132-JSAP 2019   2015

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Multi-ion sensing of buffer solutions using terahertz chemical microscopy Reviewed

Kosuke Akimune, Yuki Okawa, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Applied Physics Express   7 ( 12 )   122401   2014.12

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© 2014 The Japan Society of Applied Physics Terahertz chemical microscopy (TCM) has been proposed and developed to visualize electric potential and/or chemical changes in water solutions. To simultaneously detect two types of ions mixed in buffer solutions, five membranes for sodium ions and four membranes for potassium ions were integrated on a sensing plate, and the selectivity to each ion was evaluated. The results suggest that TCM can be used for multi-ion sensing in mixed solutions.

DOI： 10.7567/APEX.7.122401

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A terahertz chemical microscopy for an agar culture medium Reviewed

H. Nino, A. Nakamura, K. Omura, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014   2014.10

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© 2014 IEEE. In the field of life science, the research trends are to visualize 'living' materials as it is, whereas most of conventional imaging methods require pre-treatments to living samples. In our group, a terahertz chemical microscope (TCM) has been proposed and developed to investigate metabolism by the cell activity. Here the agar medium, which was generally used to cultivate cells, was immobilized on the sensing plate of TCM and the concentration of the glucose in the buffer solutions on it was detected as the terahertz amplitude shift. This result suggests that the TCM can detect the glucose in the solutions and it may possible to detect the cell activity cultivated on the agar mediums.

DOI： 10.1109/URSIGASS.2014.6930088

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Label-free detection of proteins using a terahertz chemical microscopy Reviewed

M. Ogawa, A. Nakamura, K. Omura, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014   2014.10

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© 2014 IEEE. A terahertz chemical microscopy (TCM) has been proposed and developed to visualize the distribution of chemical reactions such as antigen-antibody reaction on the sensing plate without any labels on the analyte. The TCM utilize the semiconductor-based device named a sensing plate. The sensing plate can convert the shift of the chemical potential in the magnitude on the surface of sensing plate into the amplitude of generated terahertz (THz) in the sensing plate. Thus, it enables to get images of the potential distribution on the surface of the sensing plate as the distribution of THz amplitude. Here, we demonstrate the detection of the immune reactions between the mouse immunoglobulin G (IgG) and the anti-mouse immunoglobulin G (anti-IgG). IgG was immobilized on the sensing plate and reacted with anti-IgG in the solutions with various concentrations. We also fabricated the sample wells on the sensing plate and quantitative evaluation of immune reactions were demonstrated with the anti-IgG concentration of between 5 nM and 100 nM. As a result, the change in the THz amplitude during the reaction showed the proportional relation with the concentration of reacted anti-IgG.

DOI： 10.1109/URSIGASS.2014.6930087

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Multi-ion sensing in solutions by a terahertz chemical microscopy Reviewed

K. Akimune, Y. Okawa, T. Hagiwara, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014   2014.10

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© 2014 IEEE. A terahertz chemical microscopy (TCM) has been proposed and developed in order to visualize the chemical potential changes in the water solution. In this paper, ion sensing in solutions, as an application of terahertz chemical microscopy, are introduced, and we observed the variation of amplitude of THz wave. In TCM, we detect the change in the amplitude of radiated THz wave from a THz sensing plate. The sensing plate is that the amplitude of radiated THz wave changes when chemical reactions are undergo on the THz sensing plate. We immobilized ion sensitive membranes, which can take the certain ion, on the surface of SiO2side of THz sensing plate. We dropped the sodium solution of 10-4M and 10-1M. The amplitude of radiated THz wave as the concentration of 10-1M was large in magnitude than the concentration of 10-4M where the ion sensitive membrane was immobilized. We can also visualize the concentration of ions to get image. From these results, we can detect ions in solution using TCM.

DOI： 10.1109/URSIGASS.2014.6930079

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Visualization of ion transportation in an electrolyte using an HTS-SQUID gradiometer Reviewed

Toshihiko Kiwa, Shinogo Miyazaki, Mohd M. Saari, Kenji Sakai, Akira Tsukamoto, Seiji Adachi, Tsunehiro Hato, Keiichi Tanabe, Keiji Tsukada

Physica C: Superconductivity and its Applications   504   84 - 87   2014.9

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Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-Tc superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between -0.3 V and 0.8 V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2014.04.024

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Ultrathin-film hydrogen gas sensor with nanostructurally modified surface Reviewed

Keiji Tsukada, Shuzo Takeichi, Kenji Sakai, Toshihiko Kiwa

Japanese Journal of Applied Physics   53 ( 7 )   2014.7

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The change in electrical resistance of Pt thin films on glass substrates upon exposure to hydrogen gas at room temperature was studied. The effect was detectible only for film thicknesses of less than 40 nm, and increased with decreasing thickness. Samples were also produced with a Ti film inserted between the Pt film and the glass substrate as an adhesive layer. Although the Ti film did not react with the hydrogen gas, its presence reduced the resistance change effect because it acted as a parallel resistance. To overcome this problem, the surface of the glass substrate was nanostructurally modified using porous SiO2, which led to a larger resistance change ratio. To improve the recovery time, heating by pulsed current injection was carried out. A structure consisting of Pt (5nm)/Ti (3 nm)/porous SiO2/glass was found to show a clear response to hydrogen concentrations down to about 100 ppm at room temperature. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.076701

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Magnetic susceptibility and magnetic resonance measurements of the moisture content and hydration condition of a magnetic mixture material Reviewed

K. Tsukada, T. Kusaka, M. M. Saari, R. Takagi, K. Sakai, T. Kiwa, Y. Bito

Journal of Applied Physics   115 ( 17 )   2014.5

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We developed a magnetic measurement method to measure the moisture content and hydration condition of mortar as a magnetic mixture material. Mortar is a mixture of Portland cement, sand, and water, and these materials exhibit different magnetic properties. The magnetization-magnetic field curves of these components and of mortars with different moisture contents were measured, using a specially developed high-temperature-superconductor superconducting quantum interference device. Using the differences in magnetic characteristics, the moisture content of mortar was measured at the ferromagnetic saturation region over 250 mT. A correlation between magnetic susceptibility and moisture content was successfully established. After Portland cement and water are mixed, hydration begins. At the early stage of the hydration/gel, magnetization strength increased over time. To investigate the magnetization change, we measured the distribution between bound and free water in the mortar in the early stage by magnetic resonance imaging (MRI). The MRI results suggest that the amount of free water in mortar correlates with the change in magnetic susceptibility. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4852075

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Compact AC/DC susceptometer using a high-temperature superconductor superconducting quantum interference device Reviewed

Ryuki Takagi, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEJ Transactions on Fundamentals and Materials   134 ( 6 )   369 - 374   2014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

We developed a compact susceptometer employing a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) that can measure M-H characteristics and harmonic components induced in the AC magnetic field response from a sample. In the DC function for measuring M-H characteristics, the sample was vibrated in the DC magnetic field, and the secondary magnetic field generated from the sample was detected by a DC pickup coil. In the AC function for measuring harmonic components, the sample is placed in the AC magnetic field, and the AC response was detected by an AC pickup coil. The pickup coil is connected in series with the input coil, which is inductively connected to the HTS-SQUID. Signal from the HTS-SQUID was transmitted to the lock-in amplifier, and was analyzed as the intensity and phase of the measured magnetic field. In order to clarify the basic properties of the system, we measured the AC magnetic field response from a sample in the case of changing the position between the sample and the pickup coil, and M-H characteristics when changing the DC bias magnetic field intensity. Furthermore, by analyzing the harmonic components of AC/DC magnetic field response, the system is able to measure the magnetic properties with high sensitivity and high speed. © 2014 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejfms.134.369

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DC current distribution mapping system of the solar panels using a HTS-SQUID gradiometer Reviewed

Shingo Miyazaki, Syohei Kasuya, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Seiji Adachi, Keiichi Tanabe, Keiji Tsukada

Journal of Physics: Conference Series   507 ( PART 4 )   2014

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Solar panels are expected to play a major role as a source of sustainable energy. In order to evaluate solar panels, non-destructive tests, such as defect inspections and response property evaluations, are necessary. We developed a DC current distribution mapping system of the solar panels using a High Critical Temperature Superconductor Superconducting Quantum Interference Device (HTS-SQUID) gradiometer with ramp edge type Josephson junctions. Two independent components of the magnetic fields perpendicular to the panel surface (∂Bz/∂x, ∂Bz/∂y) were detected. The direct current of the solar panel is visualized by calculating the composition of the two signal components, the phase angle, and mapping the DC current vector. The developed system can evaluate the uniformity of DC current distributions precisely and may be applicable for defect detection of solar panels. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/507/4/042026

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Development of integrated AC-DC magnetometer using high-T<inf>c</inf> SQUID for magnetic properties evaluation of magnetic nanoparticles in solution Reviewed

Mohd Mawardi Saari, Ryuki Takagi, Toki Kusaka, Yuichi Ishihara, Yuya Tsukamoto, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Physics: Conference Series   507 ( PART 4 )   2014

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We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/507/4/042035

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FET hydrogen sensor by direct heating of platinum metal gate for fast response time Reviewed

Takahiro Okuir, Yuki Usita, Shuzo Takeichi, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines   134 ( 8 )   264 - 269   2014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

© 2014 The Institute of Electrical Engineers of Japan. Improvement of the response time by direct heating of the gate catalytic metal of an FET sensor was investigated. The FET hydrogen sensor that has an adhesion layer (Ti) between the catalytic metal (Pt) and the gate insulator was fabricated. In a previous study, there was a problem in the reproducibility as some of the FET sensors displayed long recovery characteristics caused by hydrogen atoms diffused into the Pt thin film. To improve the response characteristics, two electrodes were connected to the gate metal, then, a pulse current was applied to the gate metal, having a resistance element. When applying the pulse current to the gate portion, desorption of the hydrogen remaining in the platinum thin film was accelerated because the platinum was instantaneously heated. Consequently, the hysteresis of the hydrogen was improved. Furthermore, reproducible response, fast response time and recovery time were achieved.

DOI： 10.1541/ieejsmas.134.264

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Catalytic reactions of the fuel cells visualized by THz chemical microscope

T. Kusaka, K. Koiso, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers   2014

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A terahertz chemical microscope has been developed to visualize the electric potential shift of the catalytic electrodes in fuel cells. The potential shift due to the catalytic reactions of the supplied gases could be visualized. © 2014 OSA.

DOI： 10.1364/lacsea.2014.ltu3d.6

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Magnetic nondestructive test for resistance spot welds using magnetic flux penetration and eddy current methods Reviewed

Keiji Tsukada, Kousuke Miyake, Daichi Harada, Kenji Sakai, Toshihiko Kiwa

Journal of Nondestructive Evaluation   32 ( 3 )   286 - 293   2013.9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

Resistance spot welding technologies are widely used in industry. A highly reliable monitoring method is needed to effectively weld and create a robust structure. We developed a combined technique using magnetic flux penetration and an eddy current test (ECT). The magnetic measuring system consists of a pair of magnetic probes having an induction coil and detection coil, a lock-in amplifier, a current source, and a personal computer. The magnetic flux penetration through both surfaces at the weld was measured at low frequency. The ECT was performed at each surface with multiple frequencies. The magnetic flux penetration method showed good correlation with the destructive shear test because of the change in permeability due to the formation of the nugget. The ECT method reflected the depth profile of the nugget and was effective for determining a defective product. © 2013 Springer Science+Business Media New York.

DOI： 10.1007/s10921-013-0181-0

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Evaluation of work function of the catalytic electrode in the fuel cells Reviewed

Toshihiko Kiwa, Takafumi Hagiwara, Tetsuya Kusaka, Kenji Sakai, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest   2013

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The fuel cell was fabricated on the sensing plate and the catalytic reaction of the electrode was measured using terahertz chemical microscope. Change in the amplitude of THz at the catalytic cathode and anode could be observed. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600102

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Hydrogen gas response of meta-materials made from the catalytic metal Reviewed

Takuya Sono, Mitsuhiro Shinomiya, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest   2013

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The meta-materials with a catalytic metal are fabricated on Si substrate and the hydrogen gas reaction in the THz transmittance was measured. The results suggest that two different catalytic mechanisms contribute the change in transmittance in different frequency region. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600256

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Nondestructive inspection of SiGe films using laser terahertz emission microscopy Reviewed

Akihiro Nakamura, Ken Omura, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest   2013

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Laser terahertz emission microscopy was applied to investigate the SiGe film on the Si substrate. In this study, as the initial experiment to apply LTEM to non-destructive evaluation of the strained SiGe films, the THz emission properties of the strained-SiGe were measured. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600524

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Terahertz properties from the surface of strained SiGe on Si multilayered structure Reviewed

K. Omura, A. Nakamura, T. Kiwa, Y. Yamashita, K. Sakai, K. Tsukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2013

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A Large-scale integration (LSI) has been improved by scaling contraction. Strained Si has been proposed as a higher carrier mobility than usual. We have evaluated the strained SiGe wafer by LTEM, which is a method of analyzing to detect THz waves generated by fs laser irradiated into the sample. © 2013 IEEE.

DOI： 10.1109/IRMMW-THz.2013.6665819

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Characterization of new structural ion sensor for sodium ion Reviewed

Tatsuya Komori, Takafumi Yamamoto, Kazuyo Oda, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines   133 ( 7 )   309 - 313   2013

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We developed a new structural ion sensor for measuring sodium ions without using a reference electrode. The ion sensor, which is all solid state, has a structure of double electrodes, which are integrated on the base plate, inside the sodium ion sensitive membrane. The ion sensitivity of the sensor was 41.4 mV/decade in the range of 10-1 to 10-4M. To investigate the response mechanism of the potential between two electrodes, the impedance characteristic was measured using the electrochemical impedance method. The impedance of the ion sensitive membrane changed by changing the sodium ion concentration in solution. These results suggest a correlation between the membrane potential and the membrane impedance. In conclusion, the potential difference between the electrodes is caused by the difference in ion concentration of the electrodes. © 2013 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejsmas.133.309

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Improvement of sensitivity for a compact magnetometer using HTS-SQUID with rotating sample Reviewed

Daichi Hamasaki, Naohiro Okamoto, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

2013 IEEE 14th InternationalSuperconductive Electronics Conference, ISEC 2013   134 ( 5 )   347 - 351   2013

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We previously reported a compact magnetometer using HTS-SQUID with a rotating sample for routine testing. In this study, we have improved the detection limit of the system to detect a very weak secondary magnetic field from diamagnetic material. The system consisted of a rotating sample table, a magnet with a pick-up coil, and an HTS-SQUID. The six sample cases can be fixed to a turntable using sample arms to enable multiple-detection. By rotating the sample, the velocity of the sample passing above the pick-up coil could be increased compared to the vibrating-sample method. The pick-up coil was directly coupled to a superconducting input coil of the HTS-SQUID to transfer the detected signal to the HTS-SQUID. The HTS-SQUID attached to a sensor probe was cooled by liquid nitrogen in a Dewar vessel, which was enclosed in a bilayer magnetically shielded cylindrical box. To improve the detection limit of the magnetometer's susceptibility, the noise of the applied magnetic fields was reduced, the pick-up coil shape optimized, and the accuracy of rotation speed was increased. As a result, the signal and noise ratio was improved and the magnetometer showed a high sensitivity and accuracy. © 2013 IEEE.

DOI： 10.1109/ISEC.2013.6604306

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Development of a compact magnetometer with an AC/DC magnetic field using HTS-SQUID Reviewed

Ryuki Takagi, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

2013 IEEE 14th InternationalSuperconductive Electronics Conference, ISEC 2013   2013

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Measuring the magnetic susceptibility of a material enable us to specify composition of the material. We have reported on development of a compact moving-sample magnetometer using high-temperature superconducting quantum interference device (HTS-SQUID). However, this magnetometer needs long time when we have to measure many samples. In order to solve this problem, we developed a compact magnetometer to analyze quantitative magnetic characteristics by our rapid measurement system using AC/DC functions. The optimal mounting position of pickup coils for the AC magnetic field measurement was optimized. The performance of the AC magnetic field measurement system was evaluated by measuring harmonic components of the AC magnetic response from a dispersion of iron oxide in styrene resin, when AC/DC magnetic field is applied. Using this system, the sample composition of ferromagnetic and diamagnetic substances can be evaluated from the mixed sample by measuring the harmonic components of the magnetic responses. © 2013 IEEE.

DOI： 10.1109/ISEC.2013.6604309

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Visualization of the catalytic reactions in the fuel cells using THz chemical microscope Reviewed

T. Hagiwara, T. Kusaka, T. Kiwa, K. Sakai, K. Tsukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz   2013

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THz Chemical Microscope can visualize the work function shift of the catalytic electrodes in fuel cells. We observed the variation of the terahertz wave intensity at the cathode and anode under fuel cell operation. From this result, TCM is a valuable tool for investigation and evaluation of the catalytic electrode and electrolyte in fuel cells. © 2013 IEEE.

DOI： 10.1109/IRMMW-THz.2013.6665916

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Label free immune assay using terahertz chemical microscope Reviewed

Toshihiko Kiwa, Akira Tenma, Shinji Takahashi, Kenji Sakai, Keiji Tsukada

Sensors and Actuators, B: Chemical   187   8 - 11   2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A terahertz chemical microscope (TCM) has been proposed and developed to visualize the distribution of the antibody-antigen bindings on the silicon based sensing plate without any labels and/or markers on the antibody. The sensing plate can emit the terahertz pulses by femtosecond laser pulses and the amplitude of the terahertz pulses can be related to the chemical or electric potential of the sensing plate surface at where the laser pulses are irradiated. Thus the potential distribution can be visualized as the map of the terahertz pulses amplitude. As the first demonstration of the label free immune assay, the mouse immunoglobulin G (IgG) was immobilized on the half part of the sensing plate and the mouse anti-IgG was combined with the IgG. The terahertz pulses were enhanced at where anti-IgG was combined with IgG on the sensing plate and the distributions of the IgG and anti-IgG bindings on the sensing plate were clearly seen as the TCM images. The amplitude of terahertz pulses as a function of the concentration of anti-IgG was also investigated. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2012.08.051

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Development of a compact DC magnetometer using HTS-SQUID and a rotating sample Reviewed

K. Sakai, M. M. Saari, T. Kiwa, A. Tsukamoto, S. Adachi, K. Tanabe, A. Kandori, K. Tsukada

Superconductor Science and Technology   25 ( 4 )   2012.4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We developed a compact DC magnetometer using a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) to measure very weak magnetic signals from samples such as paramagnetic and diamagnetic materials. The samples were rotated in the DC magnetic field that was detected by a normal conductive pick-up coil. The detected signal was transferred to an input coil that was inductively coupled to the SQUID. To clarify the basic characteristics of this system, the magnetic signal from a magnetic material was measured by varying the sample position and rotation speed. Then, the magnetic signal from pure water was measured under the optimized condition and a very weak magnetic signal from pure water was successfully detected. Therefore, the developed system could be applied to various non-destructive evaluation systems. © 2012 IOP Publishing Ltd.

DOI： 10.1088/0953-2048/25/4/045005

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Electric characteristics of a loop in which two junctions between a catalytic metal and a noncatalytic metal are under different hydrogen gas concentrations Reviewed

Keiji Tsukada, Kenji Sakai, Toshihiko Kiwa

Applied Physics Express   5 ( 3 )   2012.3

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To investigate the localized electrochemical properties of an electrode composed of platinum (Pt), a thin-film loop containing two junctions between the catalytic metal Pt and the noncatalytic metal titanium was fabricated. When the loop was open and only one junction was exposed to 10% hydrogen in nitrogen gas, an output voltage change of about 30 nV was generated between these two junctions. The electron density change due to the equilibrium reaction of hydrogen dissociation along the part exposed to hydrogen induced a balance between the diffusion and drift caused by the electric field at both ends of the Pt film. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.034102

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Silver Gate Field Effect Transistor for Oxygen Gas Sensor Reviewed

Keiji Tsukada, Daisuke Kiriake, Kenji Sakai, Toshihiko Kiwa

PROCEEDINGS OF SENSORDEVICES 2011: THE SECOND INTERNATIONAL CONFERENCE ON SENSOR DEVICE TECHNOLOGIES AND APPLICATIONS   5 - 7   2011

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IARIA XPS PRESS  

A silver gate field effect transistor (FET) integrated thermal controller was developed for a new type of oxygen gas sensor. It showed a threshold voltage change at a temperature as low as 80 degrees C. Oxygen response characteristics of the FET prepared with different productions of silver materials using a vacuum-evaporated membrane, printed material using silver-nanoparticles and silver epoxy were compared. The FET with a gate of silver epoxy showed the largest sensitivity of 135 mV/decade in the oxygen concentration range from 5% to 40% at 120 degrees C.

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Detection of back-side pit on a ferrous plate by magnetic flux leakage method with analyzing magnetic field vector Reviewed

Keiji Tsukada, Mitsuteru Yoshioka, Yoshihiko Kawasaki, Toshihiko Kiwa

NDT and E International   43 ( 4 )   323 - 328   2010.6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

We have developed a magnetic flux leakage (MFL) system using magnetic resistive (MR) sensors for detecting two dimensional magnetic field components, and an induction coil that generates low magnetic field strengths and extremely low frequencies. The signal at each scanned measurement point (i) was divided by the signal strength Mmes,i and phase αi by a lock-in amplifier. Using the strength Mmes,i and phase αi, we calculated the imaginary part of the signal using the common phase β. By optimization of the common phase β to the imaginary part, the analyzed scanning data curve was shown to be effective in estimating the size (depth and diameter) of back-side pits on a ferrous plate. Comparing the two dimensional magnetic field components of leakage, the imaginary part of the y-component parallel to the induced magnetic field was found to be suitable for detecting the back-side pits. © 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ndteint.2010.01.004

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Hydrogen gas diffusion imaging using multiple FET type gas sensors Reviewed

T. Kiwa, T. Yamaguchi, K. Tsubota, W. Naruyama, H. Yamada, K. Tsukada

International Journal of Advanced Mechatronic Systems   2 ( 4 )   219 - 224   2010

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Imaging of hydrogen gas concentrations were demonstrated using arrayed sensors system in the cylindrical diffusion tank-shaped simulator. The field effect transistor type hydrogen sensors with platinum gate electrode were used. The sensitivity of the sensors was around -34.1 mV/dec. and the response time was 1.2 sec. in average. By applying a sensor drive circuit to each sensor, the diffusion processes of the hydrogen gas were successfully obtained in time domain and two different processes were demonstrated using 100% hydrogen gas. These results indicate that real-time monitoring of the hydrogen gas distribution can be possible. Additionally, the calibration method of the acquired data was proposed. © 2010 Inderscience Enterprises Ltd.

DOI： 10.1504/IJAMechS.2010.033594

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Control of terahertz wave front using arrayed terahertz emission device Reviewed

K. Beppu, T. Sugimoto, T. Kiwa, K. Tsukada

IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide   2010

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Arrayed THz emission device was proposed to control the wave front of THz. The simulation results indicated the THz wave front can be tilted by changing the emission pattern of the device. The 4×4 arrayed device was fabricated and the emission pattern was successfully controlled by the bias voltages.

DOI： 10.1109/ICIMW.2010.5612739

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Chemical imaging of μ-TAS using terahertz chemical microscope Reviewed

Toshihiko Kiwa, Yuji Minami, Yusuke Kondo, Yohei Hashimoto, Iwao Kawayama, Masayoshi Tonouchi, Keiji Tsukada

IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide   2010

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A terahertz chemical microscope (TCM) has been carried out to visualize the chemical potential distribution in μ-TAS. Since the TCM can detect the chemical potential at exactly where the femtosecond laser was irradiated, the spatial resolution less than 1μm, which is limited by the wavelength of the femtosecond laser, can be achieved. The μ-TAS was fabricated on the sensing chip and the distribution of chemical potential was successfully visualized using TCM. © 2010 IEEE.

DOI： 10.1109/ICIMW.2010.5613018

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EXTREME LOW FREQUENCY MAGNETIC IMAGING METHOD FOR DETECTION OF DEFECT INSIDE WELDING PARTS OF IRON PLATE Reviewed

Keiji Tsukada, Teruki Hasegawa, Mituteru Yoshioka, Toshihiko Kiwa, Katsumi Inoue

10TH EUROPEAN CONFERENCE ON NON-DESTRUCTIVE TESTING 2010 (ECNDT), VOLS 1-5   82 - 93   2010

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INT COMMITTEE NON-DESTRUCTIVE TESTING  

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A Novel Ion Sensor Without a Reference Electrode Reviewed

Keiji Tsukada, Fumiyuki Kobayashi, Toyotaka Inoue, Toshihiko Kiwa

SENSOR LETTERS   7 ( 6 )   1163 - 1166   2009.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

We developed an ion sensor with a novel structure that does not require a reference electrode. The structure consists of a double electrode comprising an outer electrode with a hole and an inner electrode, a polymeric ion-selective membrane, and the sensor body. The ion sensitivity of a potassium ion sensor, where the hole of the outer electrode was the same size as the inner electrode, was 55 mV/decade. The sensor exhibited increased sensitivity according to the increment of the hole size The sensitivity was also dependent on the thickness of the outer membrane covering the outer electrode These phenomena were examined using a membrane potential gradient simulation

DOI： 10.1166/sl.2009.1240

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Dual gate FET hydrogen gas sensor Reviewed

K. Tsukada, M. Kariya, T. Yamaguchi, T. Kiwa, H. Yamada, T. Maehara, T. Yamamoto, S. Kunitsugu

Proceedings of IEEE Sensors   517 - 519   2009

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We developed a dual gate FET hydrogen gas sensor for application to hydrogen vehicles. The dual gate FET hydrogen sensor was integrated with Pt-gate FET to detect hydrogen and Ti-gate FET as the reference sensor in the same Si chip. Ti-gate FET has the same structure as Pt-FET except for the gate metal. The Pt-FET showed good response to hydrogen gas above 10 ppm in air, while the Ti-FET did not show any response to hydrogen gas. The differential output voltage between the Pt-FET and the Ti-FET was stable in the range of room temperature to 80° C because of the same temperature dependence of the I-V characteristic. ©2009 IEEE.

DOI： 10.1109/ICSENS.2009.5398290

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Hydrogen gas diffusion imaging using multiple FET type gas sensors Reviewed

T. Kiwa, T. Yamaguchi, K. Tsubota, W. Naruyama, H. Yamada, K. Tsukada

Proceedings of the 2009 IEEE International Conference on Networking, Sensing and Control, ICNSC 2009   282 - 286   2009

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Imaging of hydrogen gas concentrations were demonstrated using arrayed sensors system in the cylindrical diffusion tank-shaped simulator. The field effect transistor type hydrogen sensors with platinum gate electrode were used. The sensitivity of the sensors was around -34.1 mV/dec. and the response time was 1.2 sec. in average. By applying a sensor drive circuit to each sensor, the diffusion processes of the hydrogen gas were successfully obtained in time domain and two different processes were demonstrated using 100% hydrogen gas. Theseresults indicate that real-time monitoring of the hydrogen gas distribution can be possible. Additionally, the calibration method of the acquired data was proposed. © 2009 IEEE.

DOI： 10.1109/ICNSC.2009.4919287

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Evaluation of the catalytic metal for the hydrogen sensor using terahertz chemical microscope Reviewed

Takeshi Sugimoto, Yosuke Kondo, Toshihiko Kiwa, Iwao Kawayama, Masayoshi Tonouchi, Keiji Tsukada

34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009   411 - +   2009

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To develop the hydrogen sensor, the chemical potential due to the catalytic reaction of the metals are required to evaluate. The platinum and titanium layered electrode on the insulator/semiconductor layered device are fabricated as the test chip. The catalytic reaction of platinum and hydrogen gas were successfully visualized. © 2009 IEEE.

DOI： 10.1109/ICIMW.2009.5325729

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Redox reaction imaging using THz chemical microscope Reviewed

Y. Minami, T. Kiwa, I. Kawayama, M. Tonouchi, K. Tsukada

34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009   272 - 274   2009

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Terahertz chemical microscope was carried out to visualize the distribution of the redox reaction of the immobilized-enzyme. The urease films with the spot size of 3, 2, 1 mm in diameter were immobilized on a SiO2/Si/ Sapphire layered device and the laser-excited terahertz radiation from the Si layer was observed, which can be related to the chemical potential shift of the SiO2 surface. The redox reaction between the urease and the urea solution was successfully measured. © 2009 IEEE.

DOI： 10.1109/ICIMW.2009.5324691

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Laser terahertz emission microscope Reviewed

Hironaru Murakami, Naotsugu Uchida, Ryotaro Inoue, Sunmi Kim, Toshihiko Kiwa, Masayoshi Tonouchi

Proceedings of the IEEE   95 ( 8 )   1646 - 1657   2007.8

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Developments of laser terahertz (THz) emission microscope (LTEM) systems are reviewed. Femtosecond lasers can excite the THz wave emission from various electronic materials, such as semiconductors, high-temperature superconductors, manganites, multiferroic oxides, etc., due to ultrafast current modulation. Limiting the topic to semiconductors, the current modulation is realized by acceleration or deceleration of photoexcited carriers due to the local electric field extrinsically or intrinsically induced at the laser illumination spot. Thus, LTEM has a potential to visualize the local electric field distribution and photoresponse without any contacts or damages. We have ever constructed prototype free-space type and scanning fiber-probe (SFP) type LTEM systems with transmission or reflection mode. The system performance of the SFP-LTEM has been greatly improved compared with that for the prototype one. The spatial resolution of the SFP-LTEM system has a minimum spatial resolution less than 3 mum , which is defined by the laser beam diameter. The compact SFP-LTEM system, in particular the reflection system, has the potential to be utilized for wide applications as well as various materials. In this review paper, we introduce the details of the LTEM systems and example applications for the evaluation of electric field distribution in integrated circuits and supercurrent distribution in high-temperature superconductors. © 2006 IEEE.

DOI： 10.1109/JPROC.2007.898829

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Terahertz emission from catalytic-metal/semiconductor interface of hydrogen sensors

T. Kiwa, K. Tsukada, M. Suzuki, M. Tonouchi, S. Migitaka, K. Yokosawa

Optics InfoBase Conference Papers   2005

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Terahertz emission properties of catalytic-metal/semiconductor structures under hydrogen gas were investigated for non-contact and non-destructive test of hydrogen sensors. The peak amplitude of terahertz from the samples decreases with increasing the hydrogen concentration.©2005 Optical Society of America.

DOI： 10.1364/otst.2005.tud7

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Pulse current response of high-T <inf>c</inf> superconducting vortex flow transistors Reviewed

Y. Doda, T. Kiwa, I. Kawayama, H. Murakamia, M. Tonouchi

Chinese Journal of Physics   42 ( 4 II )   458 - 462   2004.8

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PHYSICAL SOC REPUBLIC CHINA  

The properties of superconducting vortex flow transistor (SVFT), which consist of a vortex flow channel and a control line for applying a magnetic field, are diagnosed by using a current pulses train method. The time-domain waveforms of the vortex flow voltage along the channel were measure using the current pulses train with the pulse width of 5 ms as input signals. The fast response of the flow voltage suggests that the heating effect is negligible and the effect of the magnetic field generated by the control line was dominant in our measurement. The vortex flow speed was estimated from the ratio of the flux flow voltage to the control current, and was found to be 8.6×10 4 m/s. We also estimated the pinning energy E p from the vortex flow speed, and found that the value of E p is around 8.6 meV for our device, which can be easily excited by a conventional Ti:sapphire femtosecond laser.

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Photomixer with superconductor detector for sub-THz generator Reviewed

Toshihiko Kiwa, Masayoshi Tonouchi

Proceedings of SPIE - The International Society for Optical Engineering   5354   121 - 128   2004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

A new type of optical-microwave conversion system has been proposed as high-stabilized oscillators and optical interfaces for superconducing circuits. The photomixer with heterodyne mixing of two lasers was applied to generate the electromagnetic waves and high-TC grain boundary Josephson junction detector was used to monitor the frequency of electromagnetic waves in real time. The current-voltage properties of Josephson junction detector were examined and the system operation up to 50 GHz was demonstrated. We also described in detail the two types of optical-microwave conversion system.

DOI： 10.1117/12.528892

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Non-contact measurement of MOSFET with zero bias voltage using the Laser-THz emission microscope Reviewed

Masatsugu Yamashita, Toshihiko Kiwa, Masayoshi Tonouchi, Kiyoshi Nikawa, Chiko Otani, Kodo Kawase

Conference Digest of the 2004 Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics   515 - 516   2004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

For inspecting electrical failures in large-scale integration (LSI) circuits, we developed the laser-THz emission microscope (LTEM), which records the map of THz emission amplitude in a sample upon excitation with fs laser pulses. We successfully observed the THz emission image of MOSFETs embedded in a test element group under zero bias voltage. This result suggests that the LTEM can be used not only for the defect localization in LSI failure analysis but also as in-line inspection and monitoring. © 2004 IEEE.

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Evaluation of spatial resolution in Laser-Terahertz emission microscope for inspecting electric faults in integrated circuits Reviewed

Masatsugu Yamashita, Toshihiko Kiwa, Masayoshi Tonouchi, Kodo Kawase

Proceedings of SPIE - The International Society for Optical Engineering   5354   104 - 111   2004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have proposed and demonstrated a nondestructive and non-contact inspection method for electrical faults using laser-Terahertz (THz) emission microscopy (LTEM). By measuring the position dependence of the amplitude of the THz emission from integrated circuits (IC) excited with femtosecond (fs) laser pulses, it is possible to investigate the electrical faults in IC. By improving the spatial resolution of the system, we successfully observed the THz emission image of a microprocessor on standby mode. The LTEM system has a spatial resolution about 3μm and it can localize electrically defective sites in the chip to within a ten square microns.

DOI： 10.1117/12.528833

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Magnetic flux letters visualized by a laser-terahertz emission microscope Reviewed

Masayoshi Tonouchi, Toshihiko Kiwa, Takashi Fukui, Hironaru Murakami

Proceedings of SPIE - The International Society for Optical Engineering   5354   112 - 120   2004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Magnetic flux letters are visualized by a laser terahertz emission microscope (LTEM). LTEM excites terahertz (THz) radiation from electronics materials with a femtosecond laser and maps the amplitude of the THz waves while scanning laser beam on the sample. Magnetic flux letters written in high-Tc superconductors are successfully imaged without destroying them.

DOI： 10.1117/12.529026

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Laser terahertz emission microscope for inspecting electrical failures in integrated circuits Reviewed

Masatsugu Yamashita, Toshihiko Kiwa, Masayoshi Tonouchi, Kiyoshi Nikawa, Chiko Otani, Kodo Kawase

IMFEDK 2004 - International Meeting for Future of Electron Devices, Kansai   34 ( 9 )   29 - 30   2004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

© 2015 IEEE. The inspection and fault analysis of semiconductor devices has become a critical issue with increasing demands for quality and reliability in circuits as stated in L. A. Krauss et al. (2001), K. Nikawa (2002) and K. Nikawa et al. (2003). Recently, we have developed a laser-terahertz (THz) emission microscope (LTEM) that can be applied for the noncontact and nondestructive inspection of the electrical faults in circuits presented in K. Nikawa et al. (2003). The LTEM can image the amplitude profile of the THz wave emitted by scanning the sample with femtosecond (fs) laser pulses. The amplitude of the THz emission generated by the transient photocurrent is proportional to the local electric field at the laser-irradiated area according to T. Kowa et al. (2003). Therefore, the LTEM image of the semiconductor device while it operates reflects the electric field distribution in the chip. By comparing the LTEM image of a damaged chip with that of a normal one, we can localize the electrical faults. In this work, we report experimental results on a biased 8-bit microprocessor, as well as unbiased MOSFETs embedded in a test element group (TEG).

DOI： 10.1109/IMFEDK.2004.1566392

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Optical-microwave converter: Superconductor/photomixer hybrid system Reviewed

Toshihiko Kiwa, Masayoshi Tonouchi

IEEE MTT-S International Microwave Symposium Digest   2   1363 - 1366   2003

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

A new type of optical-microwave converter utilizing a photomixer and a high-Tc Josephson junction detector has been developed. The frequency difference of two laser beams has been observed in the characteristic of the high-Tc Josephson junction detector. The measured response of the detector for the microwave generated by photomixing two lasers suggests that the system can work as a highly sensitive wavelength meter with accuracy of ±3.5 pm. The system operation up to 20 GHz was also demonstrated by changing the wavelength of two laser beams.

DOI： 10.1109/MWSYM.2003.1212624

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A new wavemeter for C-band using Josephson junction

T. Kiwa, M. Tonouchi

OSA Trends in Optics and Photonics Series   88   1603 - 1604   2003

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A new system that utilized photomixer and Josephson junction microwave detector has been proposed and developed. The results suggested that our system can be used as one of high precision wavemeters. © 2002 Optical Society of America.

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Terahertz radiation from amorphous GaAs thin film photoconductive switches Reviewed

T. Kiwa, I. Kawashima, M. Morimoto, H. Saijyo, S. Nashima, M. Yamashita, M. Tonouchi, M. Hangyo

CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics   2   447 - 448   1999

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

© 1999 IEEE. Low-temperature grown GaAs (LT-GaAs) has been studied as a potential material for microwave-photonic devices such as a terahertz (THz) radiation emitter. Since the preparation of the LT-GaAs generally requires a post annealing process at around 600 °C, these has been limited to be a small number of the applications combined with other materials. In the present work, we study the photoresponse of amorphous (α-) GaAs prepared at between room temperature and 250 °C by femtosecond time-domain reflection pump-probe measurements and photo-induced THz emission measurements.

DOI： 10.1109/CLEOPR.1999.811513

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