Osamu Fujiwara

Nagoya Institute of Technology, Nagoya, Aichi, Japan

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Publications (227)159.81 Total impact

  • IEEJ Transactions on Fundamentals and Materials 01/2015; 135(1):9-16. DOI:10.1541/ieejfms.135.9
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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.
    01/2015; 4(1):57-66. DOI:10.1109/MEMC.2015.7098514
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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.
    IEEJ Transactions on Fundamentals and Materials 01/2015; 135(5):253-258. DOI:10.1541/ieejfms.135.253
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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.
    IEEJ Transactions on Fundamentals and Materials 01/2015; 135(5):265-270. DOI:10.1541/ieejfms.135.265
  • 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.
    IEEJ Transactions on Fundamentals and Materials 01/2015; 135(5):259-264. DOI:10.1541/ieejfms.135.259
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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.
    Electronics and Communications in Japan 12/2014; 97(12). DOI:10.1002/ecj.11593 · 0.19 Impact Factor
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    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 10/2014; 35(7). DOI:10.1002/bem.21871 · 1.86 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). DOI:10.1002/ecj.11692 · 0.19 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 06/2014; 56(3):549-558. DOI:10.1109/TEMC.2014.2304958 · 1.35 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). · 0.12 Impact Factor
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    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). DOI:10.1002/eej.22316 · 0.12 Impact Factor
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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. DOI:10.1109/TMTT.2013.2273761 · 2.94 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; 155(3). DOI:10.1093/rpd/nct010 · 0.86 Impact Factor
  • Ryota Asayama, Jianqing Wang, Osamu Fujiwara
    IEEJ Transactions on Fundamentals and Materials 01/2013; 133(12):608-614. DOI:10.1541/ieejfms.133.608
  • Yoshinori Taka, Yoshihisa Kagawa, Osamu Fujiwara
    IEEJ Transactions on Electronics Information and Systems 01/2013; 133(12):2149-2154. DOI:10.1541/ieejeiss.133.2149
  • Ryota Asayama, Jianqing Wang, Osamu Fujiwara
    IEEJ Transactions on Fundamentals and Materials 01/2013; 133(10):537-542. DOI:10.1541/ieejfms.133.537
  • IEEJ Transactions on Electronics Information and Systems 01/2013; 133(2):350-355. DOI:10.1541/ieejeiss.133.350
  • IEEJ Transactions on Electronics Information and Systems 01/2013; 133(12):2155-2159. DOI:10.1541/ieejeiss.133.2155
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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. DOI:10.1109/TMTT.2012.2228672 · 2.94 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. DOI:10.1088/0031-9155/57/24/8427 · 2.92 Impact Factor

Publication Stats

2k Citations
159.81 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
  • 2008
    • Denso Corporation
      Kariya-chō, Aichi, Japan
  • 2007
    • National Institute of Information and Communications Technology
      Edo, Tōkyō, Japan
  • 2006
    • Chubu University
      Касугай, Aichi, Japan
  • 2003–2006
    • Osaka University
      Suika, Ōsaka, Japan
  • 2002
    • Nagoya City University
      • Department of Experimental Pathology and Tumor Biology
      Nagoya, Aichi, Japan