Osamu Fujiwara

Nagoya Institute of Technology, Nagoya, Aichi, Japan

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Publications (220)159.48 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: 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(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
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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. DOI:10.1088/0031-9155/57/23/7893 · 2.92 Impact Factor
  • 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. DOI:10.1541/ieejfms.132.51
  • 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. DOI:10.1541/ieejfms.132.345
  • 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. DOI:10.1541/ieejfms.132.383
  • 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
  • Plasma and Fusion Research 01/2012; 7:2405085-2405085. DOI:10.1585/pfr.7.2405085

Publication Stats

2k Citations
159.48 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