Osamu Fujiwara

The University of Electro-Communications, Edo, Tokyo, Japan

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Publications (251)140.14 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate electrostatic discharge (ESD) immunity testing for wearable electronic devices, the worst scenario i.e., an ESD event occurs when the body-mounted device approaches a grounded conductor is focused in this paper. Discharge currents caused by air discharges from a charged human through a hand-held metal bar or through a semisphere metal attached to the head, arm or waist in lieu of actual wearable devices are measured. As a result, it is found that at a human charge voltage of 1 kV, the peak current from the semi-sphere metal is large in order of the attachment of the waist (15.4A), arm (12.8A) and head (12.2A), whereas the peak current (10.0A) from the hand-held metal bar is the smallest. It is also found that the discharge currents through the semi-sphere metals decrease to zero at around 50 ns regardless of the attachment positions, although the current through the hand-held metal bar continues to flow at over 90 ns. These discharge currents are further characterized by the discharge resistance, the charge storage capacitance and the discharge time constant newly derived from the waveform energy, which are validated from the body impedance measured through the hand-held and body-mounted metals. The above finding suggests that ESD immunity test methods for wearable devices require test specifications entirely different from the conventional ESD immunity testing. Copyright © 2016 The Institute of Electronics, Information and Communication Engineers.
    No preview · Article · Jan 2016 · IEICE Transactions on Communications
  • Cheng JI · Daisuke ANZAI · Jianqing WANG · Ikuko MORI · Osamu FUJIWARA
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    ABSTRACT: We conduct, in accordance with IEC 61000-4-2, an electrostatic discharge (ESD) test for a small size battery-operated control circuit board in a myoelectric artificial hand system to investigate the influence of the induced noises by indirect ESDs from an ESD generator to a horizontal coupling plane (HCP) and a vertical coupling plane (VCP). A photo-coupler is set between the small size control board and a motor control circuit to suppress noise in the pulse width modulation (PWM) signals. Two types of ESD noise are observed at the output pins of PWM signals. One type is the ESD noise itself (called Type A) and the other one is the ESD noise superimposed over the PWM pulses (Type B). No matter which polarity the charge voltages of the ESD generator have, both types can be observed and the Type A is dominant in the output pulses. Moreover, the ESD interference in the HCP case is found to be stronger than that in the VCP case usually. In the PWM signals observed at the photo-coupler output, on the other hand, Type A noises tend to increase for positive polarity and decrease for negative polarity, while Type B noises tend to increase at -8 kV test level in the HCP case. These results suggest that the photocoupler does not work well for ESD noise suppression. One of the reasons has been demonstrated to be due to the driving capability of the photocoupler, and other one is due to the presence of a parasitic capacitance between the input and output of the photo-coupler. The parasitic capacitance can yield a capacitive coupling so that high-frequency ESD noises pass through the photo-coupler. © 2015 The Institute of Electronics, Information and Communication Engineers.
    No preview · Article · Dec 2015 · IEICE Transactions on Communications
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    ABSTRACT: In 2008, International Electrotechnical Commission (IEC) prescribed an immunity test (IEC61000-4-2) of electronic equipment against electrostatic discharges (ESDs), and provided a theoretical ESD current based on a Heidler's formula. For the current waveform, however, not the whole waveform but only the rise time, the first peak, and the current values at 30 ns and 60 ns are specified in the time domain along with their variability so that a commercially available ESD generator (ESD gun) shall be calibrated by checking whether or not the injected current onto an IEC recommended current target meets the IEC specification. In this study, to propose in the frequency domain the allowable variability of IEC specified current waveforms, we calculated the frequency spectra of theoretical current waveforms obtained by changing the parameters in the Heidler's formula, which were compared with those of discharge currents measured for contact discharges of commercially available ESD guns onto the IEC target. Results enabled us to give the allowable variability in the current spectra with respect to the theoretical current waveform, which is from -5 dB to +4 dB up to 400 MHz and from -6 dB to +8 dB over 400 MHz, while the measured waveforms that meet the IEC standard in the time domain have the spectra greater than +8 dB over 1 GHz due to the distortion of the current rising waveforms, although they fall in the allowable range below 1 GHz.
    Full-text · Article · Oct 2015 · IEEJ Transactions on Fundamentals and Materials
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    ABSTRACT: With the rapid increase of various uses of wireless communications in modern life, the high microwave and millimeter wave frequency bands are attracting much attention. However, the existing databases on above 6GHz radio-frequency (RF) electromagnetic (EM) field exposure of biological bodies are obviously insufficient. An in-vivo research project on local and whole-body exposure of rats to RF-EM fields above 6GHz was started in Japan in 2013. This study aims to perform a dosimetric design for the whole-body-average specific absorption rates (WBA-SARs) of unconstrained rats exposed to 6GHz RF-EM fields in a reverberation chamber (RC). The required input power into the RC is clarified using a two-step evaluation method in order to achieve a target exposure level in rats. The two-step method, which incorporates the finite-difference time-domain (FDTD) numerical solutions with electric field measurements in an RC exposure system, is used as an evaluation method to determine the whole-body exposure level in the rats. In order to verify the validity of the two-step method, we use S-parameter measurements inside the RC to experimentally derive the WBA-SARs with rat-equivalent phantoms and then compare those with the FDTD-calculated ones. It was shown that the difference between the two-step method and the S-parameter measurements is within 1.63dB, which reveals the validity and usefulness of the two-step technique.
    No preview · Article · Jul 2015 · IEICE Transactions on Communications
  • Yoshinori Taka · Yoshihisa Kagawa · Ikuko Mori · Osamu Fujiwara
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    ABSTRACT: Immunity testing for human electrostatic discharges (ESDs) is prescribed in IEC 61000-4-2, in which an ESD generator or ESD gun is used to inject into equipment under test the discharge current through a lumped resistor from a charged lumped capacitor. In actual ESD events from a charged human, however, charges distributed on the body surface should be discharged through a spark from his/her fingertip, and therefore its situation can essentially be different from that of the ESD gun. To grasp the behavior of the discharge currents for human ESDs, using a 12 GHz digital oscilloscope we measured discharge currents caused by air discharges through the fingertip or hand-held metal bar from a charged human with respect to charge voltages from 300 V to 3 kV. Results show that at charge voltages of less than 1 kV, the fingertip contact causes discharge bursts, whose occurrence frequencies increase with decreasing the charge voltages, while the hand-held metal bar at any charge voltages makes discharges complete at a time.
    No preview · Article · May 2015 · IEEJ Transactions on Fundamentals and Materials
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    ABSTRACT: In electrostatic discharge (ESD) immunity tests, it has empirically been known that contact discharge currents are enhanced by the existence of small air gaps between an ESD generator and equipment under test; however, its mechanism has not been well examined so far. In this study, to clarify the phenomena, we measured discharge currents through small air gaps from 30 µm to 1 000 µm in contact discharges of an ESD generator to an IEC current calibration target. As a result, we found that multiple current peaks appear depending on the gap length and test voltage as well, which are unlikely to occur in conventional contact discharge tests. It was also found that the contact discharge current with a small gap provides a faster rise time and larger current peak in comparison with normal contact discharge tests even at the same test voltage. A circuit approach was used to qualitatively explain the peculiar finding and revealed that the stray capacitances of the discharge electrode are first charged by a contact discharge test and then the accumulated charges are abruptly discharged due to the spark that occurs across a small gap, which gives faster rise time and larger current peaks.
    No preview · Article · May 2015 · IEEJ Transactions on Fundamentals and Materials
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    ABSTRACT: Transient characteristics and frequency spectra of impulsive electromagnetic radiation caused by ESDs were examined experimentally in order to clarify an EM radiation mechanism. The experimental system consists of a pair of spherical electrodes, a 1-18 GHz band width horn antenna and a 20 GHz bandwidth digitizing oscilloscope. Discharge voltage is less than 600 V in this experiment. As a result, the waveform duration and first peaks of the EM field radiation can be explained from a dipole antenna structure which makes a pair of spherical electrodes. Furthermore, as the excitation factors of the EM radiation from electrode elements are mentioned the current path length of the electrodes, and transient speed di/dt of discharge current. In addition, the frequency spectrum distribution of the received voltage was found to be related to the excitation path length determined by the size of the spherical electrode.
    No preview · Article · May 2015 · IEEJ Transactions on Fundamentals and Materials
  • Yoshinori Taka · Ken Kawamata · Osamu Fujiwara
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    ABSTRACT: Electrostatic discharges (ESDs) due to the collision of charged metals cause serious malfunctions in high-tech information devices. In particular, a faster collision provides a more severe ESD event, while the mechanism has not fully been elucidated, though it has widely been accepted that the faster the approach speed is, the shorter the spark length becomes. In this study, to investigate this relation quantitatively, we developed a setup for electronically measuring a spark length in air discharges of ESD generators (ESD guns), and measured spark lengths at charge voltages from + 1 kV to + 8 kV with two average approaching speeds of 20 mm/s and 100 mm/s for slow and fast approach, respectively. Measured spark lengths were validated by comparing the calculated values from two different types of empirical formulae based on the Paschen's law and experimental results shown by other researchers. As a result, we found that spark lengths measured for fixed electrodes agreed well with one of the empirical formulae, and also that the approach speeds affect spark lengths, namely the spark length for fast approach was shorter than the one for slow approach. Furthermore the measured spark lengths were found to have the same tendency with respect to approach speeds and charge voltages as other researcher's results and our previous study.
    No preview · Article · May 2015 · IEEJ Transactions on Fundamentals and Materials
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    ABSTRACT: Electrostatic discharge (ESD) generators cause electromagnetic (EM) noises not only at ESD tests but also even before and after the tests. This may provide inconsistent test results, but the mechanism has not been well examined. To explain the mechanism qualitatively, we investigated a generation source model of EM noises from an ESD generator in conjunction with the functional control sequences of built-in relay switches and the DC high voltage power supply. To validate this model, we used a magnetic field probe to measure the induced EM noises before, during, and after contact and air discharges in accordance with the corresponding timing of the functional control sequences. As a result, we confirmed that the EM noises are induced when the relay switches operate before and at ESD testing and after ESD tests for both contact and air discharges. In addition, we found that the noise peaks due to contact discharges increase with charge voltages, and the peaks just before and at the testing are relatively larger than the ones after the tests, while the peaks of the induced noises at the air discharge testing do not always increase with charge voltages, but reach a maximum at 3kV. In addition, the peaks of the induced noises at the air discharge testing become smaller than either the peaks just before the testing and those after the tests at charge voltages above 6kV. This suggests that the EM noises just before ESD testing and after the test may cause the EUT to malfunction when air discharge tests with charge voltages over 6kV are conducted. A new control sequence of the built-in relay switch was also proposed for reducing the EM noises after ESD tests, which was validated through noise measurements.
    No preview · Article · Feb 2015 · IEICE Transactions on Communications
  • Michihira Iida · Tsuyoshi Maeno · Jianqing Wang · Osamu Fujiwara
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    ABSTRACT: Electromagnetic disturbances in vehicle-mounted FM radios are mainly caused by conducted noise currents flowing through wiring-harnesses from printed circuit boards (PCBs) with the slits of ground patterns. To suppress these kinds of noise currents from PCBs, we previously performed the FDTD simulation and measurement using plural simple two-layer PCB models in which the ground patterns were divided into two parts with different widths, and revealed that the both results agreed well with the fact that the cross-talk cannot always be reduced by widening the width of divided ground patters but had the smallest values (dipping point) at specific space between the divided ground patterns. In order to clarify the above result, we calculated cross-talks using a formula developed from a simplified equivalent circuit model consisting of inductances, which were derived from their geometrical mean distance for the traces and ground patterns, and found that the calculation results also had the dipping point however the specific space and cross-talk values were different from the simulations and measurements. In the present study, to improve the calculation accuracy, we considered the non-uniformity of current distribution on the ground patterns instead the uniform current distribution, and obtained the evaluated cross-talk results which agreed better with simulations and measurements.
    No preview · Article · Jan 2015 · IEEJ Transactions on Fundamentals and Materials
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    ABSTRACT: Reverberation chamber (RC) has been recently developed and used in bio-electromagnetic (EM) field research for investigation of possible adverse health effect of EM waves to human body. Concerning the use of an RC as an exposure device, accurate dosimetry or quantification of EM energy absorbed in exposed animals inside an RC is actually of importance. However, the dosimetry of animals inside an RC is one of challenging problems due to its size and complex behavior of EM fields inside the chamber. This paper is dedicated to the demonstration of three different numerical techniques developed for dosimetry of small animals exposed to EM fields inside an RC at microwave frequencies. First we briefly review procedures of each numerical method and clarify its advantages, disadvantages, and range of applications. Then we demonstrated their validity by either experiments or cross-verification. Finally we discuss the results obtained from each numerical technique.
    No preview · Article · Jan 2015
  • C. Ji · D. Anzai · J. Wang · I. Mori · O. Fujiwara
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    ABSTRACT: In conformity with the IEC61000-4-2 standard, we conducted a case study of electrostatic discharge (ESD) tests for a small-type control board to investigate the basic coupling characteristics of induced noises by indirect ESDs. With a vertical coupling metal plane (VCP) and a horizontal coupling metal plane (HCP), the test was conducted under ±4kV and ± 8kV charging voltages. Pulse width modulation (PWM) signal outputs, which were used for controlling a pulse motor, were measured with a digital oscilloscope and were statistically analyzed with respect to their pulse widths. The analyzed results show that the interference from the ESD noises could be divided into two types: the first type is a very short pulse which is caused by the ESD noise itself, while the other one is the induced pulses overlapping on the PWM signals, which are split into several short pulses by the ESD noise. This type noise may result in causing a malfunction of the pulse motor. Furthermore, from the experiment more findings could be derived as follows: Firstly, the main interference from the indirect ESDs is the first type, and the higher charge voltage an ESD gun has, more frequently both types appear. Secondly, no matter which polarity induced noise voltages from the ESD gun have, both types of interference can be observed. Finally, the interference from the HCP is stronger than that from the VCP. © 2014 The Institute of Electronics, Information and Communication Engineer.
    No preview · Article · Dec 2014
  • I. Laakso · A. Hirata · O. Fujiwara
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    ABSTRACT: Recent advances in wireless power transmission have enabled various new applications, one of which is wireless charging of an electrical vehicle. In this application, electric power is wirelessly transmitted using strong electromagnetic fields from a coil located on the ground to another coil attached to the vehicle. In this study, we use computational modelling to investigate the human exposure to the electromagnetic fields of such a wireless charging system. The transmitted power is 7 kW and the frequency of power transmission is 85 kHz. The strengths of the external magnetic field around the vehicle and the electric field induced in the human body are compared with the exposure limits set in the international human exposure guidelines. It is found that the magnetic field strength near the vehicle exceeds the allowable field limits of international guidelines. However, the electric fields that are induced in the human body are well below the exposure limits. Therefore, kW-class wireless charging of an electrical vehicle seems to be feasible for general public use from the point of view of human exposure. © 2014 The Institute of Electronics, Information and Communication Engineer.
    No preview · Article · Dec 2014
  • Y. Kagawa · I. Mori · Y. Taka · O. Fujiwara
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    ABSTRACT: To understand the characteristics of human electrostatic discharges (ESDs), using a 12-GHz digital oscilloscope, we measured discharge currents injected into an IEC (International Electrotechnical Commission) current calibration target through the fingertip from a human body charged at a voltage of 300 V. Occurrence frequencies of the current waveforms and their cumulative relative frequency distributions were investigated. As a result, we confirmed that the finger touch causes burst discharges having current peaks of 60-ps rise time but a few ten milli-amperes, while the hand-held metal produces a one-shot discharge of the current peak with five-to-six amperes and 45-ps rise time. It was also found that the fingertip provides discharge peak currents that vary according to a log-normal distribution, while the hand-held metal bar gives current peaks following a normal distribution. © 2014 The Institute of Electronics, Information and Communication Engineer.
    No preview · Article · Dec 2014
  • K. Kawamata · S. Minegishi · O. Fujiwara
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    ABSTRACT: Frequency spectra of transient electromagnetic wave caused by electrostatic discharge in spherical electrode were examined by experimental study. The experimental system consists of a pair of spherical electrodes with different diameters, a 1-18 GHz band width horn antenna and a 20 GHz bandwidth digitizing oscilloscope. Discharge voltage is less than 600 V in this experiment. Frequency spectra and waveforms of received voltages caused by ESDs were measured in order to clarify an EM radiation mechanism. As a result, we found that the waveform duration and first peaks of the EM field radiation can be explained from a dipole antenna structure which makes the spark part of spherical electrodes. Furthermore, as the excitation factors of the EM radiation from electrode elements are mentioned the current path length of the electrodes, and transient speed di/dt of discharge current. In addition, the frequency spectrum distribution of the received voltage was found to be related to the excitation path length determined by the size of the spherical electrode. © 2014 The Institute of Electronics, Information and Communication Engineer.
    No preview · Article · Dec 2014
  • A. Hirata · S. Ohta · I. Laakso · O. Fujiwara
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    ABSTRACT: The present study investigates the relationship between the maximal temperature elevation and peak mass-averaged specific absorption rate (SAR) in different human head models, for frequencies ranging from 1 to 10 GHz. A half-wave dipole antenna is considered as a wave source at respective frequencies. Bioheat equation is used to compute the microwave-induced temperature elevation. In the post-processing, mass-averaged SAR was calculated by using different averaging algorithms which take into account the description in the international guidelines/standard. Computational results show that the ratio of the maximal temperature elevation to mass-averaged SAR depends on the averaging scheme, especially at higher frequencies. The ratios with the averaging schemes considering the contiguous tissue without the shape definition are highly affected by the power absorbed in the pinna. These results are likely to be informative for future harmonization of safety guidelines/standards. © 2014 The Institute of Electronics, Information and Communication Engineer.
    No preview · Article · Dec 2014 · IEEE International Symposium on Electromagnetic Compatibility
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    ABSTRACT: The World Health Organization (WHO) recommended the necessity of electromagnetic (FM) dosimetry evaluation of pregnant women with fetus and of children as an urgent research subject in 2006, with emphasis on studies of whole-body average specific absorption rates (WBA-SARs) in various numerical models of pregnant woman and children for the purpose of determining the safety limits of WBA-SARs. The current safety limits were determined on the basis of behavior abnormalities in healthy adult animals in radio-frequency FM exposure and FM absorption characteristics at resonant frequencies, but not in experiments using pregnant and young animals. In this investigation, we calculated the voxel SARs and WBA-SARs in anatomically detailed models of pregnant woman and 3-year-old children at their resonant frequencies. The histograms and cumulative relative distributions of the voxel SARs were also derived to determine statistical outliers in the voxel SARs for pregnant woman and 3-year-old child models. We found that the mean voxel SARs agree with the WBA-SARs, and that median voxel SARs in the pregnant woman and 3-year-old child models are 47% and 55% of their means, respectively, and the peak voxel SARs are 70 times the mean in both cases. This suggests the possibility that finite-difference time-domain (FDTD)–calculated WBA-SARs may be overestimated due to the existence of statistical outliers. It was also found that although the total number ratio of voxel SARs for the outliers is 0.36% for the pregnant woman model and 0.34% for the 3-year-old child model, WBA-SARs excluding these outliers are less than those in the pregnant woman and 3-year-old child models by 6.8% and 5.7%, respectively.
    No preview · Article · Dec 2014 · Electronics and Communications in Japan
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    ABSTRACT: For reducing the hemodialysis time of kidney disease patients, we are attempting to monitor hemodialysis quality in a real time based on dielectric constants of blood. Using a network analyzer with an open-ended coaxial-type dielectric probe, we measured complex relative permittivities ranging from 200 MHz to 6 GHz for blood of eighteen kidney disease patients before and after hemodialysis, and then derived from them admittance consisting of conductance G [S/m] and susceptance B [S/m] in order to make statistical correlation analyses between the G-B plots and blood biochemical components. As a result, we found that significant correlations are observed between the parameters of the linear approximations to the G-B plots at frequencies from 4 GHz to 6 GHz and blood urea nitrogen or creatinine before and after the hemodialysis. This finding suggests a possibility of real-time monitoring of the hemodialysis quality.
    No preview · Article · Nov 2014 · IEEJ Transactions on Fundamentals and Materials
  • K. Kawamata · S. Minegishi · O. Fujiwara
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    ABSTRACT: Radiation characteristics of transient electromagnetic field caused by ESDs (electrostatic discharges) in spherical electrode were examined by experimental study. The experimental system consists of a pair of spherical electrode, a 1-18 GHz bandwidth horn antenna and a 20 GHz bandwidth digitizing oscilloscope. Diameter of the electrodes is 19.0 mm, 25.4 mm, 30.0 mm, 50.0 mm, and 100.0 mm. Discharge voltage is less than 700 V in this experiment. Transient EM waveforms caused by ESDs were measured in order to clarify an EM radiation mechanism and characteristics. As a result, transition duration of the received voltage was found to be related to some extent to the size of the electrode. From this, one of the excitation factors due to EM radiation from the electrode elements are mentioned the current path length of the electrodes. Furthermore, polarization characteristics affected by the size of the electrodes. From this fact, as the excitation element of electromagnetic radiation, current path direction on the electrode is also important has been shown. It is possible from these results, the excitation mechanism of electromagnetic radiation is considered as a dipole elements formed by the current path on the electrode and excitation current by the discharge between the electrodes.
    No preview · Article · Oct 2014
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    ABSTRACT: This paper aims to achieve a high-quality exposure level quantification of whole-body average-specific absorption rates (WBA-SARs) for small animals in a medium-size reverberation chamber (RC). A two-step method, which incorporates the finite-difference time-domain (FDTD) numerical solutions with electric field measurements in an RC-type exposure system, has been used as an evaluation method to determine the whole-body exposure level in small animals. However, there is little data that quantitatively demonstrate the validity and accuracy of this method in an RC up to now. In order to clarify the validity of the two-step method, we compare the physical quantities in terms of electric field strength and WBA-SARs by using a direct numerical assessment method known as the method of moments (MoM) with ten homogenous gel phantoms placed in an RC with 2 GHz exposure. The comparison results show that the relative errors between the two-step method and the MoM approach are approximately below 10%, which reveals the validity and usefulness of the two-step technique. Finally, we perform a dosimetric analysis of the WBA-SARs for anatomical mouse models with the two-step method and determine the input power related to our developed RC-exposure system to achieve a target exposure level in small animals
    No preview · Article · Oct 2014 · IEICE Transactions on Communications

Publication Stats

2k Citations
140.14 Total Impact Points

Institutions

  • 2015
    • The University of Electro-Communications
      • Center for Industrial and Governmental Relations
      Edo, Tokyo, Japan
  • 1996-2015
    • Nagoya Institute of Technology
      • • Department of Computer Science and Engineering
      • • Department of Electrical and Electronic Engineering
      • • Faculty of Engineering
      Nagoya, Aichi, Japan
  • 2007-2014
    • National Institute of Information and Communications Technology
      • Electromagnetic Compatibility Laboratory
      Edo, Tokyo, Japan
  • 2003-2004
    • Osaka University
      Suika, Ōsaka, Japan