Faculty Profiles - KIWA Toshihiko

Papers - KIWA Toshihiko

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

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

10th International Workshop NDT in Progress 2019

Publishing type：Research paper (international conference proceedings)

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

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

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

Optics InfoBase Conference Papers Part F146-JSAP 2019 2019

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

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

Optics InfoBase Conference Papers Part F146-JSAP 2019 2019

Publishing type：Research paper (international conference proceedings)

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

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

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

IEEE Transactions on Magnetics 54 ( 11 ) 2018.11

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

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

DOI： 10.1109/TMAG.2018.2833852

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

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

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

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

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

DOI： 10.1109/IRMMW-THz.2018.8509878

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

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

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

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

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

DOI： 10.1109/IRMMW-THz.2018.8510464

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

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

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

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

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

DOI： 10.1109/IRMMW-THz.2018.8509884

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

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

2018 IEEE International Magnetic Conference, INTERMAG 2018 2018.10

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

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

DOI： 10.1109/INTMAG.2018.8508784

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

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

IEEE Transactions on Applied Superconductivity 28 ( 4 ) 2018.6

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

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

DOI： 10.1109/TASC.2018.2810088

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

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

IEEE Transactions on Applied Superconductivity 28 ( 4 ) 2018.6

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

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

DOI： 10.1109/TASC.2018.2795619

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

Kenji Sakai, Tsubasa Kizu, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Applied Superconductivity 28 ( 4 ) 2018.6

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

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

DOI： 10.1109/TASC.2018.2796609

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

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

Optics express 26 ( 7 ) 8232 - 8238 2018.4

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

DOI： 10.1364/OE.26.008232

Harmonics distribution of iron oxide nanoparticles solutions under diamagnetic background Reviewed

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

Journal of Magnetism and Magnetic Materials 452 145 - 152 2018.4

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

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

DOI： 10.1016/j.jmmm.2017.12.054

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

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

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

Publishing type：Research paper (scientific journal)

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

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

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

IEEE Transactions on Magnetics 54 ( 11 ) 2018

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

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

DOI： 10.1109/TMAG.2018.2845864

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

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

Optics InfoBase Conference Papers Part F113-CLEOPR 2018 2018

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

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

Studies in Applied Electromagnetics and Mechanics 43 130 - 135 2018

Publishing type：Research paper (international conference proceedings)

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

DOI： 10.3233/978-1-61499-836-5-130

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

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

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

Publishing type：Research paper (international conference proceedings)

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

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

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

Studies in Applied Electromagnetics and Mechanics 43 199 - 204 2018

Publishing type：Research paper (international conference proceedings)

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

DOI： 10.3233/978-1-61499-836-5-199

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

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

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

Publishing type：Research paper (international conference proceedings)

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

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