Faculty Profiles - KIWA Toshihiko

Magnetic thickness gauge using a Fourier transformed eddy current technique

Toshihiko Kiwa, Takayuki Hayashi, Yoshihiko Kawasaki, Hironobu Yamada, Keiji Tsukada

NDT and E International 42 ( 7 ) 606 - 609 2009.10

Language：English Publisher：ELSEVIER SCI LTD

A Fourier-transformed eddy current (FTEC) technique has been proposed and developed. This technique employs Fourier transformation analysis to analyze pulsed eddy current signals measured by magnetoresistive sensors. The advantage of this technique is that the intrinsic response, Gamp (f), of a sample material can be extracted without it being affected by the characteristics of the measurement systems. Aluminum plates with an area of 100 mm × 100 mm and various thicknesses were used as test samples. We examined the relationship between the thickness of the sample and the frequency, when Gamp (f)'s reached 90% of the maximum magnitude. The results indicate that FTEC can be used for non-contact measurements of conductive materials. We also evaluated lift-off effects for Gamp (f) for 1- and 5-mm-thick samples. The deviations of the frequencies for the 90% response were 453.386 ± 14.37 and 99.789 ± 4.13 Hz for the 1- and 5-mm-thick samples, respectively. This result indicates that the lift-off effect was reduced by the FTEC analysis. © 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ndteint.2009.04.003

Non-contact thickness gauge for conductive aterials using HTS SQUID system

Toshihiko Kiwa, Hideaki Tahara, Etsuro Miyake, Hironobu Yamada, Keiji Tsukada

IEEE Transactions on Applied Superconductivity 19 ( 3 ) 801 - 803 2009.6

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Eddy current testing using high-Tc superconductive (HTS) superconducting quantum interference devices (SQUID), was developed to realize non-contact thickness gauge measurement of conductive materials, due to their high-sensitivity to magnetic fields generated by eddy currents. A HTS SQUID pulsed eddy current system with Fourier transform analysis is proposed and demonstrated. Aluminum plates (10 × 10 mm) with thicknesses in the range of 1 to 10 mm were used as test samples. The intrinsic responses Ga(f) of the samples were successfully extracted. The slopes of these responses were estimated by linear fitting, and plotted as a function of sample thickness. The Ga(f) slopes decrease with increasing thickness of the test samples. The analysed data suggests that this system can be used as a non-contact thickness gauge for conductive materials. © 2009 IEEE.

DOI： 10.1109/TASC.2009.2019196

Magnetic image detection of the stainless-steel welding part inside a multi-layered tube structure

Takayuki Hayashi, Yoshihiko Kawasaki, Hironobu Yamada, Toshihiko Kiwa, Masaji Tamazumi, Keiji Tsukada

NDT and E International 42 ( 4 ) 308 - 315 2009.6

Language：English Publisher：ELSEVIER SCI LTD

The stainless-steel welding part inside a multi-layered tube was successfully detected using low-frequency magnetic imaging. The magnetic images were obtained by the developed measurement system, consisting of an exposure coil, magnetoresistive (MR) sensor, lock-in amplifier, x-y stage, revolving stage with a horizontal level stage and personal computer. To expose the magnetic field to a wide area of the stainless-steel sample, the radius of the exposure coil was made comparable to the sample size. The MR sensor measured the vector components of the magnetic field generated from the sample within the range of low frequencies between 50 Hz and 1 kHz. A cylindrical stainless-steel sample was fabricated as a tube by rolling a stainless-steel sheet and welding each edge using arc welding with argon as shielding gas. The normal components (Bz) and tangential components (Bx and By) to the sample surface were measured by scanning the MR sensor on the sample surface and the magnetic characteristics of each of the component images were documented. As a result, the difference in permeability between the weld area and the base material was successfully visualized as magnetic images. © 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ndteint.2008.12.006

Highly sensitive measurement of moisture content using HTS-SQUID

Keiji Tsukada, Toshihiko Kiwa, Hideaki Tahara, Etsuro Miyake, Hironobu Yamada, Akira Tsukamoto, Akihiko Kandori

IEEE Transactions on Applied Superconductivity 19 ( 3 ) 878 - 881 2009.6

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We developed a highly sensitive magnetic system for measuring moisture content using an HTS-SQUID sensor. The system consists mainly of an exposure coil, a Dewar flask containing HTS-SQUID immersed in liquid nitrogen, a cancellation coil, a lock-in amplifier, magnetically shielded box, and FLL circuit. The cancellation coil was used to eliminate the applied magnetic field at the sensor position, and then a cancellation ratio of more than -40 dB was obtained. By the high performance, the subject can be exposed to a powerful magnetic field strength in the order of μT, and a weak magnetic signal of less than tens of pT from the subject can be detected. Using a magnetic vector analysis technique, more precise measurement of moisture content is realized. © 2009 IEEE.

DOI： 10.1109/TASC.2009.2019659

Temperature control and packaging optimization of the integrated hydrogen sensor

Kousuke Tsubota, Toshihiko Kiwa, Hironobu Yamada, Tomiharu Yamaguchi, Yohei Kondo, Hirofumi Imajo, Tsutomu Hondo, Tunetoshi Maehara, Tadayoshi Yamamoto, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines 129 ( 9 ) 2 - 282 2009

Language：English

An integrated sensor chip combining a heater for temperature control and a diode for temperature monitoring was fabricated and its characteristics evaluated. Furthermore, a new packaging structure with a gas permeable film and sensor chip attached to the glass to improve the heat efficiency were developed. Using this packaging structure, the optimum working conditions and protection for the sensor chip were realized. The features of the diode were suffïcient to verify the sensor temperature. In terms of the value of heat efficiency per power consumption, we succeeded in advancing its values by about 15% compared to the glassless type. Furthermore, the time response curves for the sensor temperature and power consumption of the heater were measured. The thermal control System consists of a heater and the diode was successfully utilized to maintain the intended temperature. The heat efficiency was improved by attaching a glass and this System was found to be useful for the PPG-FET type hydrogen sensor. ©; 2009 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejsmas.129.278

Hydrogen selectivity of a proton-pumping gate FET hydrogen sensor in an AC modulation mode

Tomiharu Yamaguchi, Masanori Takisawa, Toshihiko Kiwa, Hironobu Yamada, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines 129 ( 4 ) 110 - 114 2009

Language：English

The response characteristics of a proton pumping gate FET (PPG-FET) with a triple layer gate structure (Pd/proton conducting polymer/Pt) to various gases were investigated. Two kinds of hydrogen response signals (DC and AC) were obtained from the PPG-FET when the AC bias voltage was applied between the gate electrodes of the PPG-FET. The DC signals showed high hydrogen sensitivities and the sensitivities were about -30 mV/decade. Additionally, the AC signal decreased by 10 mV with increase in the hydrogen concentration from 100 ppm to 10%. Whereas the DC signals decreased slightly with increasing oxygen concentration, the oxygen response was much smaller than the DC hydrogen sensitivities. In contrast, the AC signal hardly responded to oxygen. This is because a proton conducting polymer layer prevents the movement of oxygen ions. Additionally, the proton pumping gate FET showed good selectivity against other gases (methane, ethane, ammonia, and methanol). These results clarify the high hydrogen sensitivity of the PPG-FET in an AC modulation mode. © 2009 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejsmas.129.110

Measurement of pH in fluidic chip using a terahertz chemical microscope

Toshihiko Kiwa, Shohei Oka, Yuji Minami, Iwao Kawayama, Masayoshi Tonouchi, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines 129 ( 7 ) 221 - 224 2009

Language：English

A terahertz chemical microscope (TCM) has been developed to visualize the chemical concentration of solutions in fluidic chips. Chemical potential-terahertz transducers were newly developed and applied to the bottom surfaces of the flow channels. When femtosecond laser pulses hit the transducers, terahertz waves are radiated from them. Since the amplitude of terahertz waves can be related to the chemical potential on the surface of the device, the distribution of chemical reactions on the surface can be visualized by scanning the laser on the device. Here, we report the demonstration of mapping of pH values using TCM with a spatial resolution of less than 1 mm. The pH distribution of the flow channels filled with 0.01 M NaOH and HC1 was successfully visualized. In addition, the neutralization process was monitored. © 2009 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejsmas.129.221