Osamu Fujiwara

Nagoya Institute of Technology, Nagoya, Aichi, Japan

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Publications (210)140.43 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The present experimental study was carried out with rats to evaluate the effects of whole body exposure to 2.14 GHz band code division multiple access (W-CDMA) signals for 20 h a day, over three generations. The average specific absorption rate (SAR, in unit of W/kg) for dams was designed at three levels: high (<0.24 W/kg), low (<0.08 W/kg), and 0 (sham exposure). Pregnant mothers (4 rats/group) were exposed from gestational day (GD) 7 to weaning and then their offspring (F1 generation, 4 males and 4 females/dam, respectively) were continuously exposed until 6 weeks of age. The F1 females were mated with F1 males at 11 weeks old, and then starting from GD 7, they were exposed continuously to the electromagnetic field (EMF; one half of the F1 offspring was used for mating, that is, two of each sex per dam and 8 males and 8 females/group, except for all offspring for the functional development tests). This protocol was repeated in the same manner on pregnant F2 females and F3 pups; the latter were killed at 10 weeks of age. No abnormalities were observed in the mother rats (F0, F1, and F2) and in the offspring (F1, F2, and F3) in any biological parameters, including neurobehavioral function. Thus, it was concluded that under the experimental conditions applied, multigenerational whole body exposure to 2.14 GHz W-CDMA signals for 20 h/day did not cause any adverse effects on the F1, F2, and F3 offspring. Bioelectromagnetics © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 09/2014; · 2.02 Impact Factor
  • Ryota Asayama, Jianqing Wang, Osamu Fujiwara
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    ABSTRACT: Safety standards and guidelines for radio-frequency exposure are being set based on whole-body averaged SARs (WBA-SARs) and localized average SARs. In Japan, the WBA-SAR and 1 g localized average SAR are set at 0.4 W/kg and at 8 W/kg, respectively, except for the arms and legs and surface of body. The safety limits of WBA-SARs were determined from observing the behavior destruction of animals for radio-frequency exposure, but those of localized average SARs were determined under the assumption that a spatial peak SAR value does not exceed 20-fold WBA-SARs without their biological evidences. In this paper, to confirm whether or not the above assumption is valid, we calculated WBA-SARs and voxel SARs in the frequency range from 50 MHz to 2 GHz in anatomical-based human numerical models for pregnant woman and 3-year-child for vertically and horizontally polarized far-field exposures, and derived the histogram and cumulative relative frequency of voxel SARs to obtain the quantitative relationship between WBA-SARs and voxel SARs. As a result, we found that 99.90-percentile voxel SARs are not exceeding 20-fold WBA-SARs, while 99.00-percentile voxel SARs are smaller than 10-fold WBA-SARs in both human models.
    Electronics and Communications in Japan 09/2014; 97(9). · 0.18 Impact Factor
  • Source
    Michihira Iida, Tsuyoshi Maeno, Osamu Fujiwara
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    ABSTRACT: SUMMARY It is well known that electromagnetic disturbances in vehicle-mounted radios are mainly caused by conducted noise currents flowing through wiring harnesses from vehicle-mounted printed circuit boards (PCBs) with common ground patterns containing slits. To suppress the noise current outflow from these kinds of PCBs, we previously measured noise current outflow from simple two-layer PCBs having two parallel signal traces and different ground patterns with and without slits to reveal that making slits with open ends on the ground patterns in parallel with the traces can reduce the conducted noise currents. In the present study, using FDTD simulation we investigated the reduction effects of ground pattern size on the FM-band crosstalk noise levels between two parallel signal traces by using four types of simple PCB models having different ground patterns formed in different numbers but containing the same planar dimension slits parallel to the traces, in addition to two types of PCB models with different ground patterns divided into two parts parallel to the traces. It was found that the crosstalk noise currents for the above six types of PCBs decrease by 6.9 to 8.5 dB compared to the PCB which has a plain ground with no slits. We found that a contributing factor to the above-mentioned crosstalk reduction is reduction of the mutual inductance between the two parallel traces. In addition, in this study it is interesting to note that noise current leakage from PCBs is more significantly reduced when the size of the return ground of each signal trace is small. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 11–17, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22316
    Electrical Engineering in Japan 01/2014; 186(1). · 0.10 Impact Factor
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    ABSTRACT: A hybrid approach combining the method of moment (MoM) and the finite-difference time-domain (FDTD) method is applied to a problem of evaluating specific absorption rates (SARs) in a small rat inside a reverberation chamber (RC). The hybrid method is an alternative technique used to overcome the problem of poor convergence for a solution of the FDTD method in analyzing the RC. First, the RC with a dipole or a helical antenna is designed numerically to function properly at 2 GHz. Then, the MoM/FDTD method is used to calculate the whole-body average SAR (WBA-SAR) for a small animal inside an open cavity. The results are compared with those obtained with the FDTD method in order to verify accuracy. The SAR distributions when stirrers are rotating are also determined. Finally, it is numerically found that the ratio of the WBA-SAR of the 118 g rat to the mean squared electric field is 0.149 (mW/kg)/(V/m)$^{2}$ and an input antenna power of 2.2 W is required to produce a WBA-SAR of 4 W/kg for our designed chamber.
    IEEE Transactions on Electromagnetic Compatibility 01/2014; 56(3):549-558. · 1.33 Impact Factor
  • Michihira Iida, Tsuyoshi Maeno, Osamu Fujiwara
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    ABSTRACT: It is well known that electromagnetic disturbances in vehicle‐mounted radios are mainly caused by conducted noise currents flowing through wiring harnesses from vehicle‐mounted printed circuit boards (PCBs) with common ground patterns containing slits. To suppress the noise current outflow from these kinds of PCBs, we previously measured noise current outflow from simple two‐layer PCBs having two parallel signal traces and different ground patterns with and without slits to reveal that making slits with open ends on the ground patterns in parallel with the traces can reduce the conducted noise currents. In the present study, using FDTD simulation we investigated the reduction effects of ground pattern size on the FM‐band crosstalk noise levels between two parallel signal traces by using four types of simple PCB models having different ground patterns formed in different numbers but containing the same planar dimension slits parallel to the traces, in addition to two types of PCB models with different ground patterns divided into two parts parallel to the traces. It was found that the crosstalk noise currents for the above six types of PCBs decrease by 6.9 to 8.5 dB compared to the PCB which has a plain ground with no slits. We found that a contributing factor to the above‐mentioned crosstalk reduction is reduction of the mutual inductance between the two parallel traces. In addition, in this study it is interesting to note that noise current leakage from PCBs is more significantly reduced when the size of the return ground of each signal trace is small. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 11–17, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22316
    Electrical Engineering in Japan 01/2014; 186(1). · 0.10 Impact Factor
  • Source
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    ABSTRACT: In order to determine the whole-body exposure level in small animals inside a reverberation chamber (RC), an ideal electromagnetic (EM) environment has often been assumed inside an RC for numerical dosimetry analyses. In an RC where a strong EM coupling between antennas and animals exists, however, such an EM environment is difficult to be realized, so that it remains unknown whether or not the RC could provide a target dosimetry. In this study, we adopt the Poggio-Miller-Chang-Harrington-Wu-Tsai formulation of the method of moments to directly determine the specific absorption rate (SAR) of a rectangular dielectric phantom placed in an RC, and we demonstrated its validity via comparing the numerical temperature rise with those obtained from experiments. We then demonstrated a nonideal EM environment inside an RC using a prolate spheroid as an exposure target. Furthermore, we performed dosimetry evaluation for multiple rat-shaped tissue-equivalent phantoms inside the RC and determined their whole-body average SARs for many orientations and arrangements of the phantoms. Finally, based on our numerical results, we offered a design rule when using an RC as a whole-body exposure system for small animals.
    IEEE Transactions on Microwave Theory and Techniques 08/2013; 61(9):3435 - 3445. · 2.23 Impact Factor
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    ABSTRACT: The eye is said to be one of the most sensitive organs to microwave heating. According to previous studies, the possibility of microwave-induced cataract formation has been experimentally investigated in rabbit and monkey eyes, but not for the human eye due to ethical reasons. In the present study, the temperature elevation in the lens, the skin around the eye and the core temperature of numerical human and rabbit models for far-field and near-field exposures at 2.45 GHz are investigated. The temperature elevations in the human and rabbit models were compared with the threshold temperatures for inducing cataracts, thermal pain in the skin and reversible health effects such as heat exhaustion or heat stroke. For plane-wave exposure, the core temperature elevation is shown to be essential both in the human and in the rabbit models as suggested in the international guidelines and standards. For localised exposure of the human eye, the temperature elevation of the skin was essential, and the lens temperature did not reach its threshold for thermal pain. On the other hand, the lens temperature elevation was found to be dominant for the rabbit eye.
    Radiation Protection Dosimetry 02/2013; · 0.91 Impact Factor
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    ABSTRACT: In view of actual electromagnetic environment of multiple-frequency exposure, we have developed a whole-body exposure system for a multigeneration bio-effect test with rats at frequencies between 800 MHz and 5.2 GHz. We first experimentally evaluated the system performances such as antenna performance, electric field distribution, and specific absorption rate (SAR) in the exposure system. Then, after an experimental validation of the finite-difference time-domain modeling of the exposure system, we employed it to make a statistical SAR analysis for anatomical rat models. We first took documentary photographs of rat activity inside the exposure system every 5 min in real time. Then, by identifying the rat positions in each photograph, we derived the frequency of rats staying in various positions in the exposure system. Using the stay frequency as a weighting factor, we derived the whole-body average SAR statistical characteristics for the multiple-frequency exposure system during the entire multigeneration experimental period. The developed system and demonstrated approach provide a high-quality means for biological effect test of radio frequency exposure in wide frequency bands.
    IEEE Transactions on Microwave Theory and Techniques 01/2013; 61(1):326-334. · 2.23 Impact Factor
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    ABSTRACT: According to the international guidelines, the whole-body averaged specific absorption rate (WBA-SAR) is used as a metric of basic restriction for radio-frequency whole-body exposure. It is well known that the WBA-SAR largely depends on the frequency of the incident wave for a given incident power density. The frequency at which the WBA-SAR becomes maximal is called the 'resonance frequency'. Our previous study proposed a scheme for estimating the WBA-SAR at this resonance frequency based on an analogy between the power absorption characteristic of human models in free space and that of a dipole antenna. However, a scheme for estimating the WBA-SAR in a grounded human has not been discussed sufficiently, even though the WBA-SAR in a grounded human is larger than that in an ungrounded human. In this study, with the use of the finite-difference time-domain method, the grounded condition is confirmed to be the worst-case exposure for human body models in a standing posture. Then, WBA-SARs in grounded human models are calculated at their respective resonant frequencies. A formula for estimating the WBA-SAR of a human standing on the ground is proposed based on an analogy with a quarter-wavelength monopole antenna. First, homogenized human body models are shown to provide the conservative WBA-SAR as compared with anatomically based models. Based on the formula proposed here, the WBA-SARs in grounded human models are approximately 10% larger than those in free space. The variability of the WBA-SAR was shown to be ±30% even for humans of the same age, which is caused by the body shape.
    Physics in Medicine and Biology 11/2012; 57(24):8427-8442. · 2.70 Impact Factor
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    ABSTRACT: The World Health Organization's (WHO) recommendation on the need for further research for radio-frequency dosimetry has promoted studies on the whole-body average-specific absorption rate (WBA-SAR) in various kinds of anatomical-based numerical models. For experimental validation of GHz-band WBA-SARs in a real human, however, there have not so far been any published papers, despite the fact that, in 1982, Hill measured WBA-SARs at frequencies less than 40 MHz in human volunteers using a TEM-cell exposure system. In this study, we provide a measurement technique with a reverberation chamber for validating numerical dosimetry results on GHz-band WBA-SARs in living humans. We measured WBA-SARs at 1, 1.5 and 2 GHz for a 22 year old male volunteer, with a height of 173 cm and a weight of 73 kg, in the reverberation chamber, and compared the results with the finite-difference time-domain (FDTD) simulation. The reverberation chamber was excited by using a signal generator through an amplifier with an output power of 30-40 mW, which produced inside the chamber with the volunteer an average electric field strength of 5 V m(-1) equivalent to an average power spectral density of 6.6 μW cm(-2). The WBA-SARs were obtained from the measured S(11) and S(21) together with the power density. On the other hand, the WBA-SARs have been calculated using the FDTD method for an adult male model with almost the same physique as that of the volunteer exposed to the electromagnetic field in the reverberation chamber. From the comparison between the measured and the calculated WBA-SARs, we could confirm that the measured GHz-band WBA-SARs approximately agree with the FDTD calculated results.
    Physics in Medicine and Biology 11/2012; 57(23):7893-7903. · 2.70 Impact Factor
  • Ken Kawamata, Shigeki Minegishi, Osamu Fujiwara
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    ABSTRACT: Relation between discharge voltage and amplitude of electromagnetic radiation was examined in experimental study. The amplitude of electromagnetic radiation was proportion to the voltage gradient at the gap in the resonance experimental system using the discharge electrode with dipole configuration. In this time, we present an improved experimental system to measure the radiated electromagnetic waves in the frequency range from 1 GHz to 3 GHz using a pear of spherical electrode and a horn antenna. As a result, the amplitude of received voltage is proportion to the discharge voltage (charged voltage of the electrode) from 300V to 620V, and the received voltage is proportion to the diameter of spherical electrodes.
    01/2012;
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    ABSTRACT: In the present study, using a 50Ω tapered coaxial type adapter and a S-parameter technique, we measured the transfer impedance of a commercially available IEC calibration current target used for the immunity testing against electrostatic discharges (ESDs), which is being prescribed in the International Electrotechnical Commission (IEC) 61000-4-2, and thereby reconstructed the waveforms of discharge currents injected onto the target from their observed output voltages for contact and air discharges of an ESD generator. As a result, we found that the transfer impedance is almost 1+j0Ω at frequencies below 1GHz, while due to resonance phenomena occurring at frequencies around 2GHz and 5GHz, resistive and reactive components significantly change at frequencies over 1GHz, though their absolute values are slightly larger than 1Ω. This result has revealed that the reconstructed discharge currents agree well with the observed voltages with a rise time of almost 1ns for the contact discharges and air discharges with slow approach of an ESD gun with charge voltages above 2kV, while in the case for the observed voltage with a rapid rise time shorter than a hundred pico-seconds for the air discharges with fast approach, the reconstructed discharge current has a bit gentle rising slope and a slightly lower level of the first current peak.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(5):350-355.
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    ABSTRACT: To investigate the effects of built-in inductors on current rising waveform for contact discharges of electrostatic discharge generators (ESD guns), we simultaneously measured discharge currents and the resultant magnetic near-fields, and compared their results with those for an ESD gun with a metal cylinder in lieu of the inductor. As a result, we found that the magnetic near-field waveform is deformed by the distortion of the current rising waveform for an ESD gun with an inductor, while the ESD gun with a metal cylinder produces no distortion for the current rising waveform despite its rise time (400 ps) shorter than the International Electrotechnical Commission (IEC) specification so that there is no distortion for the corresponding magnetic near-field waveform. Using the Heidler's formula for typical discharge current waveform specified in the IEC, we calculated current rising waveform and the resultant induced output voltage of a magnetic probe, which shows that these results do not agree with those for the built-in inductor, while there is good agreement for the metal cylinder. This finding implies that immunity test results can be affected by the frequency characteristics of a built-in inductor inside an ESD gun, and thus that not only rise time but also current rising waveform of discharge currents should be specified for ESD immunity testing.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(5):362-367.
  • K. Kawamata, S. Minegishi, O. Fujiwara
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    ABSTRACT: Properties of electromagnetic field radiation due to micro gap discharge were examined in experimental study. An experimental system was consisted to measure the radiated electromagnetic waves in the frequency range from 1 GHz to 3 GHz using a pear of spherical electrode and a horn antenna. As a result, the amplitude of received voltage is proportion to the discharge voltage (charged voltage of the electrode) from 300V to 620V, and proportion to the diameter of spherical electrodes. Furthermore, a directivity of EM radiation from a pair of spherical electrode is highest at the front of electrode of 0 degree, on the one side received voltage shows lowest amplitude in side of electrode of 90 degree.
    SICE Annual Conference (SICE), 2012 Proceedings of; 01/2012
  • Ken Kawamata, Shigeki Minegishi, Osamu Fujiwara
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    ABSTRACT: The micro-gap discharge as the low voltage ESD shows very fast transition-duration of about 32 ps or less. Furthermore, the breakdown field strength in the gap was very high of about 80 MV/m in low voltage discharging of below 400V. The relationship between the breakdown field strength in the gap and the amplitude of radiated electromagnetic field was examined in experimental study. The amplitude of radiated electromagnetic field was proportion to the breakdown field strength at the gap in the resonance experimental system using the discharge electrode with dipole configuration. In this time, we present an improved experimental system to measure the amplitude of radiated electromagnetic filed in more wideband region using spherical electrodes and a horn antenna. As a result, the amplitude of radiated electromagnetic field is proportion to the discharge voltage from 300V to 620V, and the amplitude of radiated electromagnetic field was according to the diameter of spherical electrode in 1-3GHz frequency bandwidth.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(5):345-349.
  • J. Wang, K. Wake, J. Shi, S. Watanabe, O. Fujiwara
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    ABSTRACT: This paper describes two whole-body exposure systems for biological effect tests of radio frequency (RF) electromagnetic fields. The first exposure system is designed at 2 GHz band to have a feature of circular polarization for simulating a variety of coupling with humans in daily environment. The second exposure system is designed to simulate a multiple-frequency exposure between 800 MHz and 5.5 GHz. In order to get an accurate evaluation on the exposure level for rats in the exposure systems, we developed a statistical analysis tool in our systems. We first took documentary photos of rat activity in the exposure box in a real time. Then we derived the frequency of rats staying in various positions in the exposure box. Using the stay frequency as a weighting factor, we can calculate the whole-body average SAR statistical characteristics during the exposure period. The developed systems and demonstrated performances have shown their high quality and convenience as an exposure system for the above biological effect tests.
    Environmental Electromagnetics (CEEM), 2012 6th Asia-Pacific Conference on; 01/2012
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    ABSTRACT: In this study, we measured the time variation of burst electric fields leaked from a heating device in the ion cyclotron range of high-frequency in an experimental fusion facility, and analyzed their statistical characteristics such as the amplitude probability distribution (APD) and crossing rate distribution (CRD). As a result, we found that the variation of the leaked electric field level is very irregular, far from the normal distribution. Moreover, the leaked electric field variation with time may reach 400 times in one second to cross its mode value. Although so, the maximum electric field intensity itself is much smaller than the ICNIRP safety guideline. In addition, we also evaluated the possibility of electromagnetic interference to an implanted cardiac pacemaker in the measured electromagnetic environment. We found that even in the worst case the interference voltage induced in the output of the pacemaker sensing circuit does still not exceed the threshold for a malfunction.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(5):356-361.
  • Takuro Tsuji, Osamu Fujiwara
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    ABSTRACT: We measured the electric potential of a vertical coupling plane (VCP) for contact discharges of an ESD gun, and found that multiple discharges occur during 0-500 μs despite a 200-ns short time interval, whose mechanism can qualitatively be explained from a simple discharge circuit.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(5):383-384.
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    ABSTRACT: Electromagnetic disturbances in vehicle-mounted radios are mainly caused by conducted noise currents flowing through wiring-harnesses from vehicle-mounted printed circuit boards (PCBs) with common slitted ground patterns. To investigate suppression of these kinds of noise currents, previous measurements from simple two-layer PCBs with two parallel signal traces with slitted and non-slitted ground patterns, and revealed that making slits with open ends on the ground patterns in parallel with the traces can reduce the conducted noise currents. It was also discovered that the noise currents from PCBs can be suppressed even if the size of the return ground is small. Furthermore, we performed finite-difference time-domain (FDTD) simulations, using eight simple two-layer PCB models in which the ground patterns were split into two parts with different widths and one PCB model with a plane ground pattern, and found that cross-talk decreases with widening the width of the ground pattern and has the smallest values at a specific width. In the present study, to confirm the above findings experimentally, we made actual PCB samples according to exactly the same specification as the models used in the FDTD simulation, and measured the cross-talk between the two parallel signal traces with respect to the different widths of ground patterns. The results approximately agreed with the simulation.
    IEEJ Transactions on Electronics Information and Systems 01/2012; 131(12).
  • Takuro Tsuji, Kouji Himeno, Osamu Fujiwara
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    ABSTRACT: The International Electrotechnical Commission (IEC) prescribes in IEC 61000-4-2 immunity tests of electronic equipment against electrostatic discharge (ESDs), in which indirect discharges of an ESD gun onto a vertical coupling plane (VCP) in the vicinity of equipment under test (EUT) are specified for simulating human discharges to conductive materials being adjacent to the EUT. According to IEC 61000-4-2 2008-04, the VCP shall be placed at a distance of 0.1m from EUT to be tested, and the indirect discharges of an ESD gun should be conducted to the centre of a vertical edge of the VCP, though the reference arrangement of EUT is not specifically determined. In the previous study, we measured electromagnetic fields due to indirect discharges of an ESD gun onto a VCP to investigate their variations with respect to EUT positions, which showed that indirect discharges onto a vertical edge from the back side of a VCP are very likely to reduce the above-mentioned variations, while the induced voltage levels become low. In the present study, to cope with this problem, we proposed a tapered-type VCP in lieu of the IEC-specified VCP, and by using a magnetic field probe in place of EUT, we measured its induced voltages of a magnetic field probe for indirect discharges of an ESD gun onto the VCP, and examined the variations in peaks and waveform energy with respect to the probe positions. As a result, we found that the tapered-type VCP suppresses the variations in peaks by 71% and waveform energy by 40% compared to the IEC-specified VCP. To further validate the above findings, as an actual EUT, we used a commercially available ESD detector for an impulsive electric field to reveal that the tapered-type VCP provides 16%-reduced variations in its detection rates with respect to the detector positions in comparison with the present VCP.
    IEEJ Transactions on Fundamentals and Materials 01/2012; 132(1):51-56.

Publication Stats

1k Citations
140.43 Total Impact Points

Institutions

  • 1996–2014
    • Nagoya Institute of Technology
      • • Department of Computer Science and Engineering
      • • Graduate School of Engineering
      • • Faculty of Engineering
      Nagoya, Aichi, Japan
    • Tokyo Metropolitan University
      Edo, Tōkyō, Japan
  • 2009–2011
    • National Institute for Fusion Science
      • Department of Helical Plasma Research
      Toki, Gifu-ken, Japan
  • 2007–2008
    • Denso Corporation
      Kariya-chō, Aichi, Japan
    • Hachinohe Institute of Technology
      八戸, Aomori Prefecture, Japan
  • 2006
    • Guizhou Normal University
      Kuei-yang, Guizhou Sheng, China
  • 2003–2006
    • Osaka University
      Suika, Ōsaka, Japan
  • 2005
    • Motorola Mobility
      Libertyville, Illinois, United States
  • 2002
    • Nagoya City University
      • Department of Experimental Pathology and Tumor Biology
      Nagoya, Aichi, Japan