2021/07/12 更新

写真a

サカイ ケンジ
堺 健司
SAKAI Kenji
所属
ヘルスシステム統合科学学域 准教授
職名
准教授
外部リンク

研究キーワード

  • 磁気計測

  • 非破壊検査

  • 磁性材料

 

論文

  • 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年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    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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  • 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年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    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. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

    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年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    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. (C) 2019 Author(s).

    DOI: 10.1063/1.5130168

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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年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    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-T-c 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

    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年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 liftoff. 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

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

    SENSORS   19 ( 13 )   2019年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:MDPI  

    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.

    DOI: 10.3390/s19133001

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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年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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.

    DOI: 10.1109/TMAG.2019.2894904

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  • Hybrid Magnetic Sensor Combined With a Tunnel Magnetoresistive Sensor and High-Temperature Superconducting Magnetic-Field-Focusing Plates

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   29 ( 3 )   2019年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 YBa2 Cu-3 O7-delta) 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

    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年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:MDPI  

    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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  • Design of Eddy Current Testing Probe for Surface Defect Evaluation

    M. M. Saari, N. A. Nadzri, A. M. Hali, M. Ishak, K. Saka, T. Kiwa, K. Tsukada

    INTERNATIONAL JOURNAL OF AUTOMOTIVE AND MECHANICAL ENGINEERING   16 ( 1 )   6357 - 6367   2019年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:UNIV MALAYSIA PAHANG  

    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.

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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年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 Detection of Steel Corrosion at a Buried Position Near the Ground Level Using a Magnetic Resistance Sensor

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

    IEEE TRANSACTIONS ON MAGNETICS   54 ( 11 )   2018年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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.

    DOI: 10.1109/TMAG.2018.2833852

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

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

    IEEE TRANSACTIONS ON MAGNETICS   54 ( 11 )   2018年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   28 ( 4 )   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 theMNPs 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

    Kenji Sakai, Tsubasa Kizu, Toshihiko Kiwa, Keiji Tsukada

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   28 ( 4 )   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 electro-chemical 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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  • Sensitivity Improvement of Sample Rotation Measurement Method in HTS-SQUID Magnetometer for Diamagnetic Materials

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   28 ( 4 )   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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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  • pH measurements in 16-nL-volume solutions using terahertz chemical microscopy

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

    OPTICS EXPRESS   26 ( 7 )   8232 - 8238   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:OPTICAL SOC AMER  

    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. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

    DOI: 10.1364/OE.26.008232

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  • Harmonics distribution of iron oxide nanoparticles solutions under diamagnetic background

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

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   452   145 - 152   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    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 mu g/ml. The second and third harmonics were affected when the peak position of magnetic moment distribution was smaller than m = 10(-19) Am-2 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. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jmmm.2017.12.054

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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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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

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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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  • Small Eddy Current Testing Sensor Probe using Tunneling Magnetoresistance Sensors for Detection of Cracks in Steel Structures

    K. Tsukada, M. Hayashi, Y. Nakamura, K. Sakai, T. Kiwa

    2018 IEEE INTERNATIONAL MAGNETIC CONFERENCE (INTERMAG)   2018年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    K. Tsukada, T. Tomioka, S. Wakabayashi, K. Sakai, T. Kiwa

    2018 IEEE INTERNATIONAL MAGNETIC CONFERENCE (INTERMAG)   2018年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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  • A Sensitive AC Magnetometer using A Resonant Excitation Coil for Magnetic Fluid Characterization in Nonlinear Magnetization Region

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

    2018 IEEE INTERNATIONAL MAGNETIC CONFERENCE (INTERMAG)   2018年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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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年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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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  • Detection of Inner Cracks in Thick Steel Plates Using Unsaturated AC Magnetic Flux Leakage Testing With a Magnetic Resistance Gradiometer

    Keiji Tsukada, Yatsuse Majima, Yoshihiro Nakamura, Takuya Yasugi, Nannan Song, Kenji Sakai, Toshihiko Kiwa

    IEEE TRANSACTIONS ON MAGNETICS   53 ( 11 )   2017年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    In order to ensure the safety of infrastructure, it is important to be able to detect both surface and inner cracks in the thick steel plates used. However, it is difficult to use conventional magnetic measurement techniques for inspecting inner cracks in steel because of its high permeability as well as owing to the variations in it. To solve this problem, we developed a method called unsaturated ac magnetic flux leakage (MFL) testing based on a magnetic resistance gradiometer for analyzing the inner cracks in steel. The proposed method uses a sensor probe consisting of a semicircular yoke with induction coils at each end, and a gradiometer with two anisotropic magnetic resistance sensors for detecting the components perpendicular to the steel surface. The conventional MFL testing method requires a strong power source for observing the MFL in the magnetic saturation region. In contrast, in this paper, a gradiometer-based method for detecting the differential intensity and phase is used to detect low levels of magnetic leakage using a weak power source when the test steel sample is unsaturated. During the measurements, a deep inner crack could be detected by decreasing the frequency. The line-scanned differential signal exhibited a peak just above the crack position and was observed to be depth dependent. Based on these results, the method could be used to determine the position of the crack as well as its depth.

    DOI: 10.1109/TMAG.2017.2713880

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  • High-Resolution Laser-Assisted Magnetic Nanoparticle Imaging Using a High-T-C SQUID Magnetometer

    Toshihiko Kiwa, Koji Morita, Yasuaki Matsunaga, Mohd Mawardi Saari, Kenji Sakai, Keiji Tsukada

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   27 ( 4 )   2017年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    A new type of magnetic nanoparticle imaging (MPI) system has been proposed and developed. The spatial resolution of MPI systems is generally determined and limited by the size of the magnetic sensors used and the magnetic properties of the nanoparticles detected. Here, high-resolution imaging of magnetic particles was realized by combining the MPI system with a high-T-C SQUID magnetometer and laser scanning system. The spatial resolution of this system was not determined by the properties of the magnetic nanoparticles but was determined by the laser spot size focused on samples. Thus, the higher spatial resolution imparted by conventionalMPIsystems could be expected. As a demonstration of the imaging system, two cylindrical containers filled withmagnetic particles solutions were fabricated and measured. Although the containers were spaced only 2 mm apart, they could be clearly distinguished by the obtained signals. A knife-edge analysis was also applied to the obtained signals, and the spatial resolution of our system was estimated to be approximately 0.9 mm.

    DOI: 10.1109/TASC.2017.2656118

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  • Magnetic AC Impedance Analysis Method Using High-T-c SQUID Based Magnetic Measurement System

    Kenji Sakai, Tsubasa Kizu, Toshihiko Kiwa, Keiji Tsukada

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   27 ( 4 )   2017年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    A new ac impedance analysis method that uses magnetic measurements was demonstrated. The magnetic field generated from the current flowing in the sample was detected by changing the frequency of the applied voltage. To detect the generated small magnetic field, a high-temperature superconductor superconducting quantum interference device (HTS-SQUID) based magnetic measurement system was developed. The developed system could detect the magnetic field without a change in the intensity and phase in the frequency range of 1 Hz to 10 kHz. In this frequency range, the spectrum correlated with the ac impedance of the electric circuit was obtained by measuring the magnetic field from the current in the circuit. Moreover, dye-sensitized solar cells with counter electrodes of different catalysis materials were prepared, and the magnetic field from the solar cell was measured. The Cole-Cole plot of the magnetic field correlated with the ac impedance measured by a conventional method, and the difference in the shape of Cole-Cole plot was explained using the equivalent circuit analysis of the dye-sensitized solar cell. Therefore, it was clarified that is possible to obtain the spectrum correlated with ac impedance using magnetic measurements.

    DOI: 10.1109/TASC.2016.2631426

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  • Application of a HTS Coil With a Magnetic Sensor to Nondestructive Testing Using a Low-Frequency Magnetic Field

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   27 ( 4 )   2017年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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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  • Magnetic characteristics measurements of ethanol-water mixtures using a hybrid-type high-temperature superconducting quantum-interference device magnetometer

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

    AIP ADVANCES   7 ( 5 )   2017年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    The magnetic characteristics of ethanol-water mixtures were investigated using our newly developed hybrid-type magnetometer based on a high-temperature superconducting quantum-interference device. The magnetization (M-H) curves of ethanol-water mixtures show good diamagnetic characteristics. The magnetic moments of the mixture show ethanol concentration dependence. However, the variation in magnetic moment differs from the characteristics expected by considering the magnetic moment ratio between water and ethanol, and volume-reduction rate. It showed two decrement regions separated at approximately 50-60% concentration values. It is also observed that the concentration dependence of the magnetic moment measured using the sample vibration method under a uniform magnetic field and that by the sample rotation method showed slightly different characteristics. These anomalies are attributed to the formation of clustered structures in the mixture. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

    DOI: 10.1063/1.4973950

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  • Absolute-magnetic-field measurement using nanogranular in-gap magnetic sensor with second-harmonic and liquid-nitrogen-temperature operation

    Keiji Tsukada, Takuya Yasugi, Yatsuse Majima, Kenji Sakai, Toshihiko Kiwa

    AIP ADVANCES   7 ( 5 )   2017年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    To detect the absolute magnetic field, such as the earth's magnetic field, a linear magnetic response, a zero point, and thermal stability are required. We thus propose an operating method and sensor probe consisting of a nanogranular in-gap magnetic sensor (GIGS), an operational amplifier integrated circuit, and a modulation coil. The sensor probe was operated in second-harmonic mode at a liquid-nitrogen (Liq. N2) temperature. When an AC magnetic field was applied to GIGS, the second-harmonic signal was generated and modulated by the outer magnetic field to be measured. After lock-in detection, the modulated output signal showed good linearity and a zero point. Moreover, higher sensitivity and low noise with low thermal fluctuation was obtained by the cooling at Liq. N2 temperature. (C) 2017 Author(s).

    DOI: 10.1063/1.4978217

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  • Detecting Internal Defects of a Steel Plate by Using Low-Frequency Magnetic Flux Leakage Method

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

    2017 IEEE SENSORS APPLICATIONS SYMPOSIUM (SAS)   2017年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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  • Current distribution evaluation of dye-sensitized solar cell using HTS-SQUID-based magnetic measurement system

    Kenji Sakai, Kohei Tanaka, Toshihiko Kiwa, Keiji Tsukada

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   530   113 - 116   2016年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The current flowing inside a dye-sensitized solar cell (DSSC) was measured using a high-temperature superconductor superconducting quantum interference device (HTS-SQUID)-based magnetic measurement system. Further, a new evaluation method of the DSSC, which is difficult to measure using the conventional method, was investigated to improve the characteristics of the DSSC. The tangential components of the magnetic field generated from the DSSC were measured using two HTS-SQUIDs, and the intensity and direction related to the electrical current were obtained by the measured magnetic field. The DSSCs prepared with different dyes and catalytic substances showed different current-intensity mapping. The current direction was different for the DSSC with low performance. In addition, the current flowing in the ITO layer of the ITO glass substrate was also measured and the results confirmed that it had uniform distribution. These results show that the current mapping and the direction of the electrical current depend on the internal factors of the DSSC, and the detection of the magnetic field distribution generated from it is expected to lead to its new evaluation method. (C) 2016 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2016.04.002

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  • Detection of Inner Corrosion of Steel Construction Using Magnetic Resistance Sensor and Magnetic Spectroscopy Analysis

    Keiji Tsukada, Yuta Haga, Koji Morita, Nannan Song, Kenji Sakai, Toshihiko Kiwa, Weiying Cheng

    IEEE TRANSACTIONS ON MAGNETICS   52 ( 7 )   2016年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    The detection of the inner corrosion of steel construction, specifically backside corrosion of a steel plate, is highly demanded to maintain safety. Eddy-current testing (ECT) is widely used as a nondestructive testing and an evaluation method for detecting surface and subsurface flaws. However, the ECT is usually applied to non-ferromagnetic materials, but has difficulties when applied to ferromagnetic materials with high permeability, since the skin depth is smaller, and the signal-to-noise ratio (SNR) decreases due to magnetic flux fluctuation. In this paper, we developed a magnetic probe using an anisotropic magnetic resistance (AMR) sensor with the sensitivity of 1 nT/root Hz that can detect inner corrosion at extremely low frequency. We also developed an analysis method using magnetic spectroscopy to delete the magnetic flux fluctuation. To improve the SNR of the detected signal, a small cancellation coil around the AMR sensor canceled the applied magnetic field directly coupled to the sensor. The frequency of the applied magnetic field ranged from 1 Hz to 1 kHz. The sensor output at each frequency was lock-in detected. The weak ac magnetic field was applied to the initial permeability region of the magnetization curve. The obtained magnetic vector signal consisting of a real part and an imaginary part at each frequency was plotted as magnetic spectroscopy, and the magnetic component of the eddy current and the magnetic component of the magnetization of the steel were separated. By using the magnetic component of the eddy current, the thickness of an iron steel plate thinner than 16 mm could be measured. Moreover, the shape of the back-side corrosion was determined by scanning with the magnetic probe.

    DOI: 10.1109/TMAG.2016.2530851

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  • Label-free detection of low-molecular-weight samples using a terahertz chemical microscope

    Takuya Kuwana, Masahiro Ogawa, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

    APPLIED PHYSICS EXPRESS   9 ( 4 )   2016年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    A terahertz chemical microscope (TCM) has been proposed and developed to visualize the distribution of biomolecular interactions on a sensing plate without any labels. In this study, the concanavalin A (Con A)-D-(+)-mannose (mannose) interaction was detected using the TCM with mannose applied as the analyte and Con A immobilized on the sensing plate. To demonstrate this interaction, the amplitude of terahertz pulses as a function of Con A-mannose interaction time, as well as the Con A-mannose coupling concentration, was evaluated. The results suggest that coupling kinetics may be evaluated using a TCM. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.9.042401

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  • Hybrid Type HTS-SQUID Magnetometer With Vibrating and Rotating Sample

    Keiji Tsukada, Koji Morita, Yasuaki Matsunaga, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   26 ( 3 )   2016年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    Highly sensitive measurement of the very weak magnetic characteristics of magnetic particles in solution or of a solution itself is required for applications, such as biomedical examinations. In this paper, higher sensitivity and additional performance with relaxation measurement and harmonic signal detection were achieved by an improvement of the driving mechanism and the high-resolution electric magnet, and optimization of the superconducting quantum interference device (SQUID) detection unit. A servomotor was used for sample vibration and rotation with precise control and high speed. For detection of the M-H characteristics, the sample was vibrated under the magnetic field in the electromagnet. For measuring the relaxation of the magnetization, the sample was rotated. A first-order differential pickup coil with a normal conducting wire connected to the input coil of a high-temperature superconductor-SQUID was used to detect the magnetic signal from the sample. High-resolution measurement of the magnetic moment on the order of 10(-11) A m(2) was achieved with this system configuration. An ac magnetic field with a dc bias could then be applied to the sample for detection of the harmonic signal. The magnetic relaxation signal from the sample was measured by another of the same type of differential detection coil equipped outside of the electric magnet by rotating, instead of vibrating, the sample. The magnetization curve for a low concentration of iron nanoparticles with a superparamagnetic character in the solution was successfully measured using the developed magnetometer, and the relaxation phenomenon was also characterized.

    DOI: 10.1109/TASC.2016.2531632

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  • Compact AC/DC Susceptometer Using a High-Temperature Superconducting Quantum Interference Device

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

    ELECTRONICS AND COMMUNICATIONS IN JAPAN   99 ( 3 )   31 - 37   2016年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

    We developed a compact susceptometer employing a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) that can measure the M-H characteristics and the 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 a 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 placed in an 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. A signal from the HTS-SQUID was transmitted to a 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 while varying the relative positions of the sample and the pickup coil, and the M-H characteristics while varying the dc bias magnetic field intensity. Furthermore, by analyzing the harmonic components of the ac/dc magnetic field response, the proposed system can measure magnetic field properties with high sensitivity and at high speed.

    DOI: 10.1002/ecj.11779

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  • Improvement of Sensitivity of a Compact Magnetometer by Using HTS-SQUID with Rotating Sample

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

    ELECTRICAL ENGINEERING IN JAPAN   194 ( 2 )   9 - 14   2016年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY  

    We have improved a previously developed compact magnetometer using HTS-SQUID with a rotating sample. In the previous system, attenuation of the rotational speed had resulted in deformation of the averaged waveform signal, reducing the reproducibility of measurements. In this paper, we have used a better motor in order to decrease the attenuation of the rotational speed for precise averaging of the output signal and improvement of the signal-to-noise ratio. To improve sensitivity, we also optimized the pickup coil and compared the signal-to-noise ratio of circular and elliptical pickup coils having the same number of turns, resistance, and inductance. As a result, the signal-to-noise ratio was improved with high accuracy and the magnetometer showed a susceptibility sensitivity of 3.8x 10(-9) emu. (C) 2015 Wiley Periodicals, Inc.

    DOI: 10.1002/eej.22732

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  • Development of Terahertz Chemical Microscope for Detecting Small Molecules

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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    Masaya Inamo, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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  • Combinatorial Sensing of Catalytic Materials Using Terahertz Chemical Microscope

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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:INT FREQUENCY SENSOR ASSOC-IFSA  

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

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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:INT FREQUENCY SENSOR ASSOC-IFSA  

    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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  • pH Measurements Of nano-liter Solutions Using THz Technology

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

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

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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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  • Development of a Magnetic Phase Map for Analysis of the Internal Structure of a Spot Weld

    Nannan Song, Keisyu Shiga, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

    ELECTROMAGNETIC NONDESTRUCTIVE EVALUATION (XIX)   41   302 - 311   2016年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOS PRESS  

    Resistance spot welding technologies are widely used in industry. We previously reported an analysis method for examining the strength of spot-welded parts with the eddy current test (ECT) by using a wide range of frequencies from high to low. However, liftoff has a non-negligible effect. Increasing the liftoff significantly decreases the magnetic field intensity for mapping. The magnetic field phase is not affected by changes in liftoff. The measured phase map of the magnetic field showed a good correlation with the results of the destructive shear test. In this paper, we report an analysis and imaging method for examining spot-welded parts based on the phase of a magnetic field by using a wide range of frequencies from high to low. With the magnetic phase map, the internal structure of a spot weld was visualized for easy understanding of the results of this method. Thus, this method can easily be applied to industrial production. This new method was validated through both experimental and simulation results.

    DOI: 10.3233/978-1-61499-639-2-302

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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-c SQUID magnetometer

    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年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The magnetization curve of iron oxide nanoparticles in low-concentration solutions was investigated by a highly sensitive high-T-c 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 held 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 mu g/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. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jmmm.2015.06.090

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

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

    IEEE TRANSACTIONS ON MAGNETICS   51 ( 11 )   2015年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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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  • Ion Transportation of Electrolytes in a Flow Channel Mapped by an HTS SQUID Scanning System

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   25 ( 3 )   2015年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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 (K-3[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

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   25 ( 3 )   2015年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    Moisture content evaluated by magnetic signal change measured by rotating-sample magnetometer using high-temperature 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-c SQUID Magnetometer Detection Unit for Evaluation of Magnetic Nanoparticles in Solution

    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年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    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-c superconducting quantum interference device magnetometer

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

    JOURNAL OF APPLIED PHYSICS   117 ( 17 )   2015年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    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 mu g/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. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4919043

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

    K. Sakai, K. Morita, Y. Haga, T. Kiwa, K. Inoue, K. Tsukada

    2015 IEEE MAGNETICS CONFERENCE (INTERMAG)   2015年

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    記述言語:英語   出版者・発行元:IEEE  

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

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

    APPLIED PHYSICS EXPRESS   7 ( 12 )   2014年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    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. (C) 2014 The Japan Society of Applied Physics.

    DOI: 10.7567/APEX.7.122401

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

    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年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    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. (c) 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

    Keiji Tsukada, Shuzo Takeichi, Kenji Sakai, Toshihiko Kiwa

    JAPANESE JOURNAL OF APPLIED PHYSICS   53 ( 7 )   2014年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    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 (5 nm)/Ti (3 nm)/porous SiO2/glass was found to show a clear response to hydrogen concentrations down to about 100 ppm at room temperature. (C) 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

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

    JOURNAL OF APPLIED PHYSICS   115 ( 17 )   2014年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    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. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4852075

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  • Stabilization method for signal drifts in terahertz chemical microscopy

    Toshihiko Kiwa, Kenji Sakai, Keiji Tsukada

    OPTICS EXPRESS   22 ( 2 )   1330 - 1335   2014年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:OPTICAL SOC AMER  

    A stabilization method for signal drifts in terahertz chemical microscopy (TCM) due to unexpected chemical potential changes in sample solutions was proposed and developed. The sensing plate was separated into two areas: a detection area and a control area. The detection area radiated a THz pulse whose amplitude was related to both the chemical reactions in the sample solutions and unexpected potential changes. The THz pulse from the control area was related only to unexpected potential changes. In the proposed system, the THz pulse from each area was interfered and detected. By adjusting the timing of the positive peak of the THz pulse from the detection area and the negative peak of the THz pulse from the control area, we detected the difference in both peaks as the interference signal. Thus, the signal deviation of 390 when the environmental condition changes in the temperature range of 38 C and the pH range of 8.33 was stabilized to be the signal deviation of 31. As the result, the TCM with stabilization method could detect the signal shift of 121 when the 275-nmol/L immunoglobulin G was immobilized on the sensing plate. (C) 2014 Optical Society of America

    DOI: 10.1364/OE.22.001330

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

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

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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 SiO2 side of THz sensing plate. We dropped the sodium solution of 10(-4) M and 10(-1) M. The amplitude of radiated THz wave as the concentration of 10(-1) M was large in magnitude than the concentration of 10(-4) M 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.

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  • Development of integrated AC-DC magnetometer using high-T-c SQUID for magnetic properties evaluation of magnetic nanoparticles in solution

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

    11TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS2013), PTS 1-4   507   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-T-c SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The fluxtransformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibratingsample 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.

    DOI: 10.1088/1742-6596/507/4/042035

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

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

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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  • A terahertz chemical microscopy for an agar culture medium

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

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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.

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

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

    11TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS2013), PTS 1-4   507   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    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 (partial derivative Bz/partial derivative x, partial derivative Bz/partial derivative 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.

    DOI: 10.1088/1742-6596/507/4/042026

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  • Magnetic evaluation of a solar panel using HTS-SQUID

    Toshihiko Kiwa, Yohei Fukudome, Shingo Miyazaki, Mohd Mawardi Saari, Kenji Sakai, Keiji Tsukada

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   494   195 - 198   2013年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The magnetic evaluation system of a solar panel using HTS-SQUID has been proposed and developed. A normal pick-up coil was applied to detect the tangential magnetic field to the panel surface. Since the detected field could be related to the currents of the solar panels, the electric properties of the solar panels could be evaluated. In this work, the evaluation of the electric properties of the commercial solar panels as well as the electric circuits made by the discrete devices on the circuit board was visualized. (C) 2013 Elsevier B. V. All rights reserved.

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  • Label free immune assay using terahertz chemical microscope

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

    SENSORS AND ACTUATORS B-CHEMICAL   187   8 - 11   2013年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元: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. (C) 2012 Elsevier B. V. All rights reserved.

    DOI: 10.1016/j.snb.2012.08.051

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  • Magnetic Nondestructive Test for Resistance Spot Welds Using Magnetic Flux Penetration and Eddy Current Methods

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

    JOURNAL OF NONDESTRUCTIVE EVALUATION   32 ( 3 )   286 - 293   2013年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元: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.

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  • Compact Rotating-Sample Magnetometer for Relaxation Phenomenon Measurement Using HTS-SQUID

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   23 ( 3 )   2013年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    A compact magnetometer that uses a high-temperature superconductor superconducting quantum interference device (HTS-SQUID) that can measure relaxation phenomena was developed, and its characteristics were evaluated. For measuring magnetic relaxation, a pick-up coil was designed to be fixed at any position in the circle described by a rotating-sample. The pick-up coil was directly connected to an input coil, which is inductively connected to the HTS-SQUID, and the secondary induced magnetic field from the sample was detected with time delay after magnetization. Using the developed system, magnetic signals with time delay from pure water were detected, and the magnetic signal intensity decreased with increasing time delay. This magnetic signal with time delay was not caused by the sample case and the magnetization due to the leaked magnetic field distribution of the permanent magnet used for sample magnetization. Thus, the developed system could detect magnetic signals during the magnetic relaxation process.

    DOI: 10.1109/TASC.2012.2234324

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  • Optimization of the Detection Technique for a Vibrating-Sample Magnetometer Using High-T-c SQUID

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

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   23 ( 3 )   2013年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    We have developed a compact vibrating-sample magnetometer that uses a high-temperature superconductor superconducting quantum interference device (high-T-c SQUID) and a normal conductive pickup coil. To further increase the sensitivity of the developed system, we consider a technique to detect harmonic components induced at the pickup coil. We optimized the geometry of the pickup coil and sample to maximize the harmonic signals and compared the harmonic signals induced from different shapes of coils using simulation and experimental methods. The simulation and the experimental results agreed well, indicating that the optimized geometry of the pickup coil improves the induced harmonic components. Improvement in sensitivity with reduced mechanical noise can be attained using this detection technique.

    DOI: 10.1109/TASC.2012.2227919

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  • Magnetic Detection of Currents in an Electrolytic Cell Using High-T-C SQUID

    Toshihiko Kiwa, Yohei Fukudome, Shingo Miyazaki, Mohd Mawardi Saari, Kenji Sakai, Akira Tsukamoto, Seiji Adachi, Keiichi Tanabe, Akihiko Kandori, Keiji Tsukada

    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY   23 ( 3 )   2013年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

    A magneto-electrical cyclic voltammetry has been proposed and developed. This measurement method utilized three electrodes: a counter, a working, and a reference electrode, as the conventional voltammetry uses and the magnetic field by the currents were detected. Thus, the current distribution in the electrolyte cells during the voltammetry measurements could be visualized. In this work, the current in the cell was observed during the pulse voltammetry using the high-T-C SQUID with the normal pick-up coils. The pick-up coil was aligned parallel to the surface of the cell. Obtained magnetic signals could be related to the current measured by the conventional method.

    DOI: 10.1109/TASC.2012.2228736

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  • Hydrogen Gas Response of Meta-Materials Made From the Catalytic Metal

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

    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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

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

    2013 38TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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  • Nondestructive inspection of SiGe films using laser terahertz emission microscopy

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

    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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  • Evaluation of Work Function of the Catalytic Electrode in the Fuel Cells

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

    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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

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

    2013 IEEE 14TH INTERNATIONAL SUPERCONDUCTIVE ELECTRONICS CONFERENCE (ISEC)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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  • Visualization of the catalytic reactions in the fuel cells using THz Chemical Microscope

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

    2013 38TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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  • Absorption Characteristics of Composite Electromagnetic Wave Absorber Made of Sendust Particles Dispersed in Polystyrene Resin

    Yuki Hongo, Kenji Sakai, Yuuki Sato, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN XV   566   215 - 218   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    A low-cost composite electromagnetic wave absorber made of sendust dispersed in resin was developed that does not contain any rare metals. In this study, spherical sendust particles with average particle sizes of approximately 5 and 20 mu m were dispersed in polystyrene resin at volume ratios in the range 20-40 vol% to broaden the absorption frequency bandwidth at frequencies above 10 GHz. The optimal volume ratios of sendust with average particle sizes of approximately 5 and 20 mu m were found to be approximately 30 and 35 vol%, respectively. Electromagnetic wave absorbers can be flexibly designed by controlling the volume ratio of spherical sendust particles in resin.

    DOI: 10.4028/www.scientific.net/KEM.566.215

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  • Development of a Compact Magnetometer with an AC/DC Magnetic Field Using HTS-SQUID

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

    2013 IEEE 14TH INTERNATIONAL SUPERCONDUCTIVE ELECTRONICS CONFERENCE (ISEC)   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    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.

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  • Work function shifts of catalytic metals under hydrogen gas visualized by terahertz chemical microscopy

    Toshihiko Kiwa, Takafumi Hagiwara, Mitsuhiro Shinomiya, Kenji Sakai, Keiji Tsukada

    OPTICS EXPRESS   20 ( 11 )   11637 - 11642   2012年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:OPTICAL SOC AMER  

    Terahertz chemical microscopy (TCM) was applied to visualize the distribution of the work function shift of catalytic metals under hydrogen gas. TCM measures the chemical potential on the surface of a SiO2/Si/sapphire sensing plate without any contact with the plate. By controlling the bias voltage between an electrode on the SiO2 surface and the Si layer, the relationship between the voltage and the THz amplitude from the sensing plate can be obtained. As a demonstration, two types of structures were fabricated on the sensing plate, and the work function shifts due to catalytic reactions were visualized. (C) 2012 Optical Society of America

    DOI: 10.1364/OE.20.011637

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  • Development of a Compact Moving-Sample Magnetometer Using High-T-c Superconducting Quantum Interference Device

    Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Seiji Adachi, Keiichi Tanabe, Akihiko Kandori, Keiji Tsukada

    JAPANESE JOURNAL OF APPLIED PHYSICS   51 ( 4 )   2012年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    We developed a compact moving-sample magnetometer that uses a high-temperature superconductor-superconducting quantum interference device (high-T-c SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-T-c SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1 x 10(-7) emu. (C) 2012 The Japan Society of Applied Physics

    DOI: 10.1143/JJAP.51.046601

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

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

    SUPERCONDUCTOR SCIENCE & TECHNOLOGY   25 ( 4 )   2012年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元: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.

    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

    Keiji Tsukada, Kenji Sakai, Toshihiko Kiwa

    APPLIED PHYSICS EXPRESS   5 ( 3 )   2012年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    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. (c) 2012 The Japan Society of Applied Physics

    DOI: 10.1143/APEX.5.034102

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  • Changes in Work Function and Electrical Resistance of Pt Thin Films in the Presence of Hydrogen Gas

    Keiji Tsukada, Hirotsugu Inoue, Fumiya Katayama, Kenji Sakai, Toshihiko Kiwa

    JAPANESE JOURNAL OF APPLIED PHYSICS   51 ( 1 )   2012年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

    The changes in the electrical properties, such as work function and resistance, of Pt thin films in the presence of hydrogen gas were studied. They were simultaneously measured with a flow-through cell at different concentrations of hydrogen gas in atmosphere containing gaseous nitrogen and that containing air. The resistance was measured by a four-terminal sensing method and the relative work function changes were measured using a field effect transistor. In both atmospheres, the resistance decreased as the concentration of hydrogen gas increased. This result was repeatable only in air because of the differences in the dynamic mechanism of increased density of electrical carriers inside the Pt film as a result of diffused H atoms. In the nitrogen atmosphere, the diffused H atoms were not easily released because of the surface barrier. On the other hand, oxygen gas reacted with H atoms at the surface and this reaction accelerated atom release into air. The work function showed repeatable responses in both atmospheres, but the response characteristics were different. The equilibrium reaction between the adsorption and desorption of hydrogen occurred at the surface in the nitrogen atmosphere, whereas the equilibrium reaction of hydrogen and oxygen to form water molecules occurred in air. The changes in work function and resistance in the presence of hydrogen were due to changes in dissociated hydrogen intensity in the bulk, as well as to the surface reactions. (C) 2012 The Japan Society of Applied Physics

    DOI: 10.1143/JJAP.51.015701

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  • Improvement of Absorbing Frequency Bandwidth of Composite Electromagnetic Wave Absorber Made of Granular Sendust Particles Dispersed in Polystyrene Resin

    Y. Hongo, K. Sakai, Y. Sato, S. Yoshikado

    PROCEEDINGS OF PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM (PIERS 2012)   1150 - 1155   2012年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    Composite electromagnetic wave absorber made of sendust dispersed in resin is low-cost and contains no rare metal. In this study, granular shaped sendust particles with the average particle size of approximately 5 and 20 mu m were dispersed in polystyrene resin with the volume ratio of 20-40 vol% in order to broaden the absorbing frequency bandwidth in the frequency range from above 10 GHz. Experimental results reveal that absorbing frequency bandwidth is drastically improved and the optimal volume mixture ratio of sendust is approximately 30 vol% for the average particle size of approximately 5 mu m and approximately 35 vol% for approximately 20 mu m.

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  • Design of Composite Electromagnetic Wave Absorber Made of Fine Spherical Metal Particles Dispersed in Polystyrene Resin

    Y. Guan, K. Sakai, Y. Sato, S. Yoshikado

    PIERS 2011 MARRAKESH: PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM   404 - 410   2011年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    For the purpose of designing electromagnetic wave absorbers which can operate at frequencies above 1 GHz, the ability to control the relative complex permeability mu(r)* and the relative complex permittivity epsilon(r)* for the composite made of fine metal particles dispersed in polystyrene resin was investigated. Method to calculate mu(r)* for sample made of dispersed metal particles having the distribution of the size is proposed. In order to clarify the effect of particle shape on mu(r)* and epsilon(r)* samples made of dispersed non-spherical aluminium particles in polystyrene resin were prepared and the values of mu(r)* and epsilon(r)* were compared. Moreover, in order to clarify the effect of particle size on mu(r)* and epsilon(r)*, samples made of dispersed spherical particles of copper with the size of several micro meters were prepared. The calculated value of mu(r)* using the proposed formula considering the size distribution was more in agreement with the measure value compared with that calculated using formula applicable to single particle size. Proposed formula was also applicable to calculation of mu(r)* with multiple kinds of average particle size. Moreover, the calculated value of mu(r)* was qualitatively in agreement with the measured value for the samples with different shape or size. The measured values of mu(r)* for the composite made of the mixture of copper particles with two kinds of average particle size were in agreement with the calculated values. Thus, it was found that the values of mu(r)* and absorption characteristics can be controlled by the particle size distribution, the particle shape, or mixing ratio of particles with different average particle size.

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  • Silver Gate Field Effect Transistor for Oxygen Gas Sensor

    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年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元: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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  • Composite Electromagnetic Wave Absorber Made of Ni-Zn Ferrite Particles Dispersed and Isolated in an SiO2 Medium

    Kenji Sakai, Yang Guan, Yuuki Sato, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN XIV   485   229 - 232   2011年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability mu(*)(r), the relative complex permittivity epsilon(*)(r),and return loss were investigated for a composite made of Ni-Zn ferrite and SiO2. When ferrite particles were dispersed and isolated in an SiO2 medium, the frequency dependence of mu(*)(r) was different from that for a composite made of SiO2 particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO2 was selected, the return loss was less than -20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO2 particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO2 medium.

    DOI: 10.4028/www.scientific.net/KEM.485.229

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  • Effect of Particle Shape on Absorption Characteristics of Composite Electromagnetic Wave Absorber Made of Sendust Particles Dispersed in Polystyren Resin

    K. Sakai, Y. Guan, Y. Sato, S. Yoshikado

    3RD INTERNATIONAL CONGRESS ON CERAMICS (ICC3): ADVANCES IN ELECTRO CERAMICS   18   2011年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    The frequency dependences of the relative complex permeability mu(*)(r), the relative complex permittivity epsilon(*)(r) and the return loss for the composite made of sendust flakes or spherical sendust particles dispersed in polystyrene resin were investigated in the frequency range from 1 to 40 GHz. The values of epsilon(*)(r) increased when sendust flakes were dispersed in polystyrene resin and the frequency dependence of mu(*)(r) was different in the particles shape of sendust. Therefore, absorption characteristics depended on the particle shape of sendust and the absorption of electromagnetic waves with a wide bandwidth in the frequency range from 10 and 20 GHz could be achieved using spherical sendust particle with a low volume mixture ratio.

    DOI: 10.1088/1757-899X/18/9/092019

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  • Preparation and Evaluation of Composite Electromagnetic Wave Absorbers Made of Aluminum Fine Particles Dispersed in Polystyrene Medium

    Norizumi Asano, Yoichi Wada, Kenji Sakai, Shinzo Yoshikado

    ELECTRONICS AND COMMUNICATIONS IN JAPAN   93 ( 1 )   30 - 40   2010年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SCRIPTA TECHNICA-JOHN WILEY & SONS  

    We developed composite electromagnetic wave absorbers consisting of dispersed aluminum fine particles in a polystyrene medium and evaluated their properties in order to realize single-layer electromagnetic wave absorbers, with good absorption in the gigahertz region. Polystyrene particles with two diameters (approximately 200 mu m and 1 mu m) and fine aluminum particles were mixed by mechanical milling. The mixture was heated above the melting point of polystyrene and then cooled naturally in air. The frequency characteristics of the complex relative permeability and the complex relative permittivity were calculated from the values of the scattering parameters of a coaxial line loaded with a sample of a toroidal-core shape. Both the diamagnetism and the magnetic loss increased in proportion to the volume mixing ratios of aluminum particles up to approximately 34 vol% for samples made of polystyrene particles with approximately 200 mu m or 1 mu m diameter. The diamagnetism was almost frequency-independent and the magnetic loss decreased with increasing frequency for all samples. These results were in agreement with qualitative theoretical prediction. (C) 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 93(1): 30-40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10169

    DOI: 10.1002/ecj.10169

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  • Composite electromagnetic wave absorber made of soft magnetic material and polystyrene resin and control of permeability and permittivity

    Kenji Sakai, Norizumi Asano, Yoichi Wada, Shinzo Yoshikado

    JOURNAL OF THE EUROPEAN CERAMIC SOCIETY   30 ( 2 )   347 - 353   2010年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCI LTD  

    The frequency dependences of the relative complex permeability mu(r)*, the relative complex permittivity epsilon(r)* and the absorption characteristics for composite electromagnetic wave absorbers made of polystyrene resin and sendust particles or permaLloy particles were investigated in the frequency range from 1 to 40 GHz. The size of sendust particles was varied between approximately 5 and 20 mu m and the particle size dependence of mu(r)* was observed. The value of mu(r)* was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed. A metal-backed single-layer absorber made of sendust particles or permalloy particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. In addition, a composite made of 5 mu m particles exhibited a return loss of less than -20 dB in the frequency range of not only several GHz but also above 30 GHz. (C) 2009 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jeurceramsoc.2009.05.044

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  • Effect of Sendust Particle Size on Absorption Characteristics of Composite Electromagnetic Wave Absorber

    Kenji Sakai, Yoichi Wada, Yuuki Sato, Shinzo Yoshikado

    ASIAN CERAMIC SCIENCE FOR ELECTRONICS III AND ELECTROCERAMICS IN JAPAN XII   421-422   451 - 454   2010年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    The effects of the particle size of sendust, which is an alloy of Al 5%, Si 10%, and Fe 85%, on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated in the frequency range from 1 to 40 GHz. The size of senclust particles was varied between approximately 5 and 20 mu m. A metal-backed single-layer absorber made of 20 mu m sendust particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. Meanwhile, a composite made of 5 mu m particles exhibited a return loss of less than -20 dB in the frequency range of not only several GHz but also above 30 GHz. In addition, the relative complex permeability mu(r)* was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed.

    DOI: 10.4028/www.scientific.net/KEM.421-422.451

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  • Composite Electromagnetic Wave Absorber Made of Both Sendust and Aluminum Particles Dispersed in Polystyrene Resin

    Kenji Sakai, Yang Guan, Yuuki Sato, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN XIII   445   197 - 200   2010年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    To design an electromagnetic wave absorber with good absorption properties at frequencies above 1 GHz, the frequency dependences of the relative complex permeability mu(r)*, the relative complex permittivity epsilon(r)*, and return loss were investigated for the composite made of both sendust (an alloy of Al 5%, Si 10%, and Fe 85%) and aluminum particles dispersed in polystyrene resin. It was found that the frequency dependence of mu(r)* for this composite can be changed by adjusting the particle size of aluminum and the volume mixture ratio of sendust and aluminum. Therefore, a flexible design of an absorber with good absorption characteristics was proposed based on the ability to control mu(r)*. The composite made of both sendust and aluminum was found to exhibit a return loss of less than -20 dB in the frequency range of not only several GHz but also around 20 GHz if appropriate volume mixture ratio and particle size were selected.

    DOI: 10.4028/www.scientific.net/KEM.445.197

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  • FLEXIBLE DESIGN OF COMPOSITE ELECTROMAGNETIC WAVE ABSORBER MADE OF ALUMINUM AND SENDUST PARTICLES DISPERSED IN POLYSTYRENE RESIN

    Kenji Sakai, Yoichi Wada, Yuuki Sato, Shinzo Yoshikado

    ADVANCES IN MULTIFUNCTIONAL MATERIALS AND SYSTEMS   216   137 - 152   2010年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER CERAMIC SOC  

    For the purpose of designing electromagnetic wave absorbers with good absorption properties at frequencies above 1 GHz, the frequency dependences of the relative complex permeability mu(r)*, the relative complex permittivity epsilon(r)*, and the return loss were investigated for the composite made of both sendust (an alloy of Al 5%, Si 10%, and Fe 85%) and aluminum particles dispersed in polystyrene resin. The effects of the magnetic resonance caused by sendust and magnetic moments caused by sendust and aluminum on the frequency dependence of mu(r)* were observed in the composite made of both sendust and aluminum. Thus, it was found that the frequency dependence of mu(r)* for the composite made of sendust can be changed by adding aluminum particles in the composite made of sendust. Moreover, when each volume mixture ratio of sendust and aluminum was varied without changing the total volume mixture ratio of sendust and aluminum, the frequency dependence of mu(r)* was different despite the value of epsilon(r)* was almost the same. This result leads to a flexible design of an absorber with good absorption characteristics because the frequency dependence of mu(r)* can be controlled by selecting suitable volume mixture ratio of sendust and aluminum without changing the vale of epsilon(r)*. The composite made of both sendust and aluminum was found to exhibit a return loss of less than -20 dB in the frequency range of not only several GHz but also around 20 GHz. Furthermore, the reduction in weight of an absorber could be also possible since the aluminum is low mass density.

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  • Evaluation of Composite Electromagnetic Wave Absorber Made of Isolated Ni-Zn Ferrite or Permalloy

    Kenji Sakai, Kiyohiro Hiraki, Shinzo Yoshikado

    ELECTRONICS AND COMMUNICATIONS IN JAPAN   92 ( 5 )   14 - 22   2009年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SCRIPTA TECHNICA-JOHN WILEY & SONS  

    It has been found that if a composite material consists of a magnetic material isolated in a dielectric medium, the relative complex permeability of the composite material does not obey Lichtenecker's law, which is well known to explain the relative complex permeability and permittivity of composite materials. This characteristic leads to the absorption of electromagnetic wave power at frequencies above 1 GHz. We proposed an isolation model to simulate the frequency dependence of the relative complex permeability and developed a composite electromagnetic wave absorber made of ferrite-SiO(2) or a permalloy-polystyrene system in which magnetic materials are isolated. The mechanical milling method was employed to isolate the magnetic material in the dielectric medium. Ni-Zn ferrite particles could be isolated in the SiO(2) medium and the measured values of the relative complex permeability were close to those calculated from the isolation model. Consequently, this absorber could absorb electromagnetic wave power in the frequency range front 1 to 3 GHz. Permalloy particles were also isolated in a polystyrene resin medium. The absorber made of permalloy and polystyrene resin exhibited good absorption characteristics in the frequency range between 3 and 8 GHz. (C) 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(5): 14-22, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ec.j.10045

    DOI: 10.1002/ecj.10045

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  • Design of Composite Electromagnetic Wave Absorber Made of Fine Aluminum Particles Dispersed in Polystyrene Resin by Controlling Permeability

    K. Sakai, Y. Wada, Y. Sato, S. Yoshikado

    PIERS 2009 MOSCOW VOLS I AND II, PROCEEDINGS   42 - 49   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    The ability to control the relative complex permeability mu(r)* of composites made of fine aluminum particles dispersed in polystyrene resin was investigated for the purpose of designing electromagnetic wave absorbers with good absorption properties at frequencies above 1 GHz. The volume mixture ratio V and particle size of aluminum were varied and the frequency dependences of mu(r)*, the relative complex permittivity epsilon(r)*, and the return loss were measured. Theoretical values of mu(r)* for the composites were also calculated using Maxwell's equations. The measured value of the real part of mu(r)*, was found to decrease with increasing frequency in the low frequency range. However, at high frequencies, mu(r)'. was almost independent of frequency and decreased proportionately with mu(r)' In addition, the measured value of mu(r)'' was found to be proportional to V and inversely proportional to the aluminum particle size. These results showed good agreement with the calculated values of mu(r)' and mu(r)''. An electromagnetic wave absorber with a flexible design was proposed based on the ability to control mu(r)' and mu(r)'' independently by adjusting V and the aluminum particle size.

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  • Composite Electromagnetic Wave Absorber Made of Aluminum Particles or Sendust Particles Dispersed in Polystyrene Medium

    Kenji Sakai, Yoichi Wada, Yuuki Sato, Shinzo Yoshikado

    POLYMER-BASED SMART MATERIALS - PROCESSES, PROPERTIES AND APPLICATION   1134   23 - +   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:MATERIALS RESEARCH SOC  

    The frequency dependences of the relative complex permeability mu(r)*, the relative complex permittivity epsilon(r)* and the absorption characteristics for composite electromagnetic wave absorbers made of polystyrene resin and sendust (an alloy of Al, Si and Fe) or aluminum fine particles were investigated in the frequency range from 1 to 40 GHz. The size and volume Mixture ratio of sendust and aluminum were varied. A metal-backed single-layer absorber made of sendust and that of aluminum absorbed more than 99% of electromagnetic wave power at frequencies above 10 GHz. Moreover, the values of mu(r)* was shown to be controlled by adjusting the volume mixture ratio and particle size of sendust or aluminum, and an electromagnetic wave absorber with a flexible design was proposed.

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  • Design of Composite Electromagnetic Wave Absorber Made of Soft Magnetic Materials Dispersed and Isolated in Polystyrene Resin

    Kenji Sakai, Yoichi Wada, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN XI   388   257 - 260   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    Composite electromagnetic wave absorbers made of a soft magnetic material (permalloy or sendust) and polystyrene resin were investigated [1]. The volume mixture ratio of magnetic material was varied in the range from 18 vol% to 75 vol%. The composites with the low volume mixture ratio of soft magnetic material absorbed more than 99 % of electromagnetic wave power in the frequency range from 1 GHz to 10 GHz. The values of the real part mu(r)' of the relative complex permeability mu(r)* for both magnetic materials were less than unity at frequencies above approximately 6 GHz as the volume mixture ratio of magnetic material increased. This result suggests the possible realization of an electromagnetic wave absorber that can operate above 10 GHz.

    DOI: 10.4028/www.scientific.net/KEM.388.257

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  • Preparation and evaluation of composite electromagnetic wave absorbers made of fine aluminum particles dispersed in polystyrene medium

    Y. Wada, N. Asano, K. Sakai, S. Yoshikado

    PIERS 2008 CAMBRIDGE, PROCEEDINGS   279 - 285   2008年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    We developed composite electromagnetic wave absorbers made of fine aluminum particles dispersed in a polystyrene medium and evaluated their properties in order to realize metal-backed single-layer electromagnetic wave absorbers with a good absorption property in the GHz region. Both the magnetization and the magnetic loss caused by the eddy current flowing on the surface of the aluminum particles increased proportionally to the volume mixture ratio of the aluminum particles for all samples. The magnetization was almost independent of frequency but the magnetic loss decreased with increasing frequency for all samples. These results were in agreement with qualitative theoretical predictions.

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  • Design of composite electromagnetic wave absorber made of soft magnetic materials dispersed and isolated in polystyrene resin

    K. Sakai, Y. Wada, S. Yoshikado

    PIERS 2008 HANGZHOU: PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM, VOLS I AND II, PROCEEDINGS   1322 - 1327   2008年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    Composite electromagnetic wave absorbers made of a soft magnetic material (permalloy or sendust) and polystyrene resin were investigated. The volume mixture ratio of magnetic material was varied in the range from 18 vol% to 75 vol%. The composites with the low volume mixture ratio of soft magnetic material absorbed more than 99% of electromagnetic wave power in the frequency rage from 1 GHz to 12 GHz. The values of the real part mu(r)' of the relative complex permeability mu(r)* for both magnetic materials were less than unity at frequencies above approximately 6 GHz as the volume mixture ratio of magnetic material increased. This result suggests the possible realization of an electromagnetic wave absorber that can operate above 10 GHz.

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  • Composite electromagnetic wave absorber made of permalloy or sendust and effect of sendust particle size on absorption characteristics

    K. Sakai, Y. Wada, S. Yoshikado

    PIERS 2008 CAMBRIDGE, PROCEEDINGS   286 - 293   2008年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELECTROMAGNETICS ACAD  

    The effects of the size and shape of sendust particles on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated. We also investigated the difference in the absorption characteristics between permalloy and sendust. The sendust particles were granular or flakes and those of permalloy were granular. The size of sendust particles was varied in the range from approximately 5 to 20 mu m. A metal-backed single layer absorber made of a composite containing small sendust particles absorbed more than 99% of electromagnetic wave power in the frequency range from 1 to 3 GHz. The values of the real part mu'(r) of the relative complex permeability mu(r)* for both magnetic materials became less than unity and had a minimum value at frequencies above 10 GHz. The composite made of small sendust particles exhibited a return loss of less than -20 dB at frequencies near 35 GHz for a suitable sample thickness.

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  • Preparation of TiO2 thin films by electrophoresis deposition method for dye-sensitized solar cells

    Kunio Yamamoto, Kenji Sakai, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN X   350   151 - +   2007年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    The purpose of this study is to prepare high-quality TiO2 thin films for dye-sensitized solar cells using the electrophoresis method. A high-quality TiO2 thin film has a thickness of approximately 10 mu m and no crack on the surface. In this study, TiO2 thin films were deposited by changing the configuration of electrophoresis electrodes. When electrodes were set parallel to horizontal and ITO glass substrate was set in the upper electrode, an excellent TiO2 thin film of approximately 10 mu m thickness was obtained by depositing very thin TiO2 films as a buffer layer. The new film has the highest open-circuit voltage and short-circuit current density.

    DOI: 10.4028/www.scientific.net/KEM.350.151

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  • Evaluation of composite electromagnetic wave absorber made of polystyrene resin and permalloy or sendust

    Kenji Sakai, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN X   350   239 - +   2007年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    The frequency dependences of the complex permeability mu(r)*, complex permittivity epsilon(r)*, and return loss were investigated for composite electromagnetic wave absorbers made of soft magnetic materials (permalloy or sendust) and polystyrene resin. For permalloy, two types of particle shape were used: grain-type or flake-type. The volume mixture ratio of magnetic materials was varied in the range from 40 % to 70 %. The values of the real part mu' and imaginary part mu" of mu(r)* increased with increasing mixture ratio of magnetic materials. The frequency dependence of mu(r)* for flake-type permalloy composite was similar to that for sendust composite. All absorbers showed the absorption of electromagnetic waves in the frequency range above 1 GHz.

    DOI: 10.4028/www.scientific.net/KEM.350.239

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  • Evaluation of characteristics of composite electromagnetic wave absorbers

    Kenji Sakai, Kiyohiro Hiraki, Hiroki Kusunoki, Takatoshi Kondo, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN IX   320   193 - 196   2006年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    It is found through simulation that composite electromagnetic wave absorbers made of Ni-Zn ferrite and SiO2 particles, which are isolated in the continuous medium of Ni-Zn ferrite, show good absorption. In particular, absorbers show absorption in the frequency regions both below and above 1 GHz for the mixing ratio of SiO2 of 80 mol%. To simulate the complex permeability of the composite materials, we considered some arrangements of SiO2 in the Ni-Zn ferrite medium. Measured values of complex permeability are close to simulated ones above 1 GHz.

    DOI: 10.4028/www.scientific.net/KEM.320.193

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  • New method to adsorb dye molecules for dye sensitized solar cell

    Kenji Sakai, Kenji Fujimura, Shinzo Yoshikado

    ELECTROCERAMICS IN JAPAN IX   320   219 - 222   2006年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:TRANS TECH PUBLICATIONS LTD  

    TiO2 thin films for the dye sensitized solar cell have been deposited by the electrophoresis method using the ultra fine particles of TiO2. To adsorb much dye molecules on the TiO2 film, electrophoresis method and vacuum impregnation have been tried. The quality of TiO2 thin film and the amount of the dye molecules adsorbed on the thin film affect the energy conversion efficiency of the dye sensitized solar cell. The condition to adsorb large amounts of dye molecules on the TiO2 film was discussed. The values of open-circuit voltage and short-circuit current increased using both vacuum impregnation and electrophoresis method to adsorb dye molecules.

    DOI: 10.4028/www.scientific.net/KEM.320.219

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▼全件表示

共同研究・競争的資金等の研究

  • 磁場計測による交流インピーダンススペクトルの推定と局所領域の電気化学反応評価

    研究課題/領域番号:18K04168  2018年04月 - 2021年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    堺 健司

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    配分額:4420000円 ( 直接経費:3400000円 、 間接経費:1020000円 )

    申請者が提案した磁気計測による局所領域の電気化学インピーダンススペクトル(Localized Electrochemical impedance spectroscopy: LEIS)評価法の最適な計測条件や空間分解能について,電気化学反応で動作する色素増感型太陽電池を作製し測定することで検討を行った。
    超高感度磁気センサのSQUIDの感度軸を変化させ3軸方向の磁場を測定した結果,電池内を流れる電流と垂直な磁場を測定した場合にS/N比が高く,電気化学インピーダンスに対応した磁気信号を取得できることが分かった。
    また,実際のデバイスで提案する磁場計測を用いたLEIS評価が可能であるかを実証するために,1つの太陽電池セル内で白金と炭素の2種類の触媒材料を使用し,部分的に電気化学インピーダンスが異なる太陽電池を作製し測定を行った。その結果,各触媒材料の上側にSQUIDを配置して測定した磁場の周波数特性は触媒材料に応じて異なる値を示し,この違いは各触媒材料に対応する電気化学インピータンスと定性的に一致することが分かった。一方,この太陽電池を既存の電気化学インピーダンス評価装置で測定した結果,2つの触媒を含む電極間の測定評価であるため,各領域の特性を評価することはできず,本手法の優位性を示すことができた。
    さらに,触媒材料の違いが表れる周波数の磁場を印加し,触媒の境界を含む領域で磁場分布を測定し触媒材料の違いを可視化した。その結果,各領域の触媒に対応して磁場強度が異なる画像が得られることが分かり,この場合境界付近の磁場信号が変化する範囲は3 mm程度であった。この結果より開発した計測システムの空間分解能が明らかになったが,本研究では数百マイクロメートルから1 mm程度の領域における電気化学インピーダンス変化の検出を目的としており,更なる改善が必要であることも明らかになった。

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  • 超高感度磁気センサを用いた電流分布可視化システムと電池開発への応用

    研究課題/領域番号:15K21188  2015年04月 - 2017年03月

    日本学術振興会  科学研究費助成事業 若手研究(B)  若手研究(B)

    堺 健司

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    配分額:4160000円 ( 直接経費:3200000円 、 間接経費:960000円 )

    電流が作る磁場分布を計測して電池内の電流分布を評価する装置を開発し,次世代の太陽電池である色素増感型太陽電池の特性と電流分布の関係を調べた。その結果,太陽電池を構成する色素や触媒材料が異なっても太陽電池の電気的特性が大きく低下しない限り,セル内での電流分布は均一であることが分かった。一方,太陽電池の電気的特性が大きく低下した場合は,その内部で電流分布に変化が生じることも分かった。さらに,太陽電池の内部構造を詳しく解析可能な交流インピーダンス解析を磁気計測により行えることも実証たした。この成果を応用し,これまでの測定法では困難であった局所領域の交流インピーダンス解析も期待できる。

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  • メタマテリアルを用いた電磁波吸収体の作製と評価

    研究課題/領域番号:09J02415  2009年 - 2010年

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    堺 健司

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    配分額:1200000円 ( 直接経費:1200000円 )

    電磁波吸収体は,無線通信機器が使用される環境で通信障害などの問題を解決する重要なデバイスである。無線通信機器が数GHz~数十GHzの電磁波を使用し,使用周波数の変化も激しいため,高周波化,周波数の変化に対応した電磁波吸収体が求められている。また,実用化を考えると低コスト化,量産可能なことも重要となる。電磁波の吸収は,吸収体材料の複素比透磁率と複素比誘電率により決定されるが,本研究ではこれらの値を人工的に制御でき,しかも汎用材料のみで構成可能なメタマテリアルを電磁波吸収体に応用することを試みた。メタマテリアルは導体などの周期配列により実現できるが,本研究では樹脂中に磁性体粒子を均一分散して粒子の周期配列によりメタマテリアルを実現した.また,立体構造を容易に作製できる光造形法を用いて,樹脂の周期構造を作製し,金属を蒸着して導体の周期配列を作製して電磁波吸収体へ応用することも試みた.
    樹脂を溶解し磁性体粒子と混合することで,粒子間に樹脂の層が形成され,個々の粒子が孤立して樹脂中に分散した.この方法で作製した試料は,数GHz~数十GHzで市販の吸収体よりも良好な吸収特性を示し,粒子の分散方法により吸収特性が改善できることを明らかにした.この成果は,特殊な材料を必要とせず材料の構造のみで特性を改善できるため,低コスト化など吸収体の設計において有用な技術となる.また,電磁波の吸収に有効であるコイルの周期配列を,光造形法と金属の蒸着を組み合わせ容易に作製できることを示した.作製したコイルの周期配列に対して10~20GHzの電磁波を入射し,透過波と反射波を調べた結果,金属を蒸着しなかった試料の特性と異なる結果が得られた.従って,最適な周期配列や形状を選択することで高機能な吸収体の作製が期待でき,光造形法を用いて実用的な電磁波吸収体を容易に設計できることを明らかにした。

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担当授業科目

  • センサデバイス工学 (2021年度) 前期  - その他

  • センシング工学特論 (2021年度) 前期  - 火1~2

  • ヘルスシステム統合科学アドバンストインターンシップ (2021年度) 通年  - その他

  • ヘルスシステム統合科学専門英語 (2021年度) 後期  - その他

  • ヘルスシステム統合科学演習 (2021年度) 後期  - その他

  • ヘルスシステム統合科学特別研究 (2021年度) 通年  - その他

  • ヘルスシステム統合科学総合演習 (2021年度) 後期  - その他

  • 先進病院実習 (2021年度) 前期  - その他

  • 光計測工学特論 (2021年度) 前期  - 月5~6

  • 医療機器材料学概論 (2021年度) 前期  - その他

  • 医療機器材料学概論 (2021年度) 前期  - 水1~2

  • 技術表現発表学 (2021年度) 後期  - その他

  • 技術表現発表学 (2021年度) 後期  - その他

  • 計測システム応用学 (2021年度) 後期  - その他

  • 電子計測 (2021年度) 第2学期  - 月1,月2,木5,木6

  • 電気法規・施設管理 (2021年度) 1・2学期  - 木7,木8

  • 電気法規・施設管理1 (2021年度) 第1学期  - 木7,木8

  • 電気法規・施設管理2 (2021年度) 第2学期  - 木7,木8

  • 電磁気学B (2021年度) 第3学期  - 月5,月6,木3,木4

  • 電磁気学Ⅱ (2021年度) 第3学期  - 月5,月6,木3,木4

  • 電磁気学Ⅲ (2021年度) 第3学期  - 月5,月6,木3,木4

  • センサデバイス工学 (2020年度) 前期  - その他

  • センシング工学特論 (2020年度) 前期  - 火1,火2

  • ヘルスシステム統合科学アドバンストインターンシップ (2020年度) 通年  - その他

  • ヘルスシステム統合科学専門英語 (2020年度) 後期  - その他

  • ヘルスシステム統合科学演習 (2020年度) 後期  - その他

  • ヘルスシステム統合科学特別研究 (2020年度) 通年  - その他

  • ヘルスシステム統合科学総合演習 (2020年度) 後期  - その他

  • 光計測工学特論 (2020年度) 前期  - 月5,月6

  • 医療機器材料学概論 (2020年度) 前期  - 水1,水2

  • 技術表現発表学 (2020年度) 後期  - その他

  • 計測システム応用学 (2020年度) 後期  - その他

  • 電子計測 (2020年度) 第2学期  - 月1,月2,木5,木6

  • 電気法規・施設管理 (2020年度) 1・2学期  - 木5,木6

  • 電気法規・施設管理1 (2020年度) 第1学期  - 木5,木6

  • 電気法規・施設管理2 (2020年度) 第2学期  - 木5,木6

  • 電磁気学B (2020年度) 第3学期  - 月5,月6,木3,木4

  • 電磁気学Ⅱ (2020年度) 第3学期  - 月5,月6,木3,木4

  • 電磁気学Ⅲ (2020年度) 第3学期  - 月5,月6,木3,木4

▼全件表示