T. Shiozawa

Chubu University, Касугай, Aichi, Japan

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Publications (73)74.74 Total impact

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    ABSTRACT: This study investigated the temperature elevation in the eye of anatomically based human head models for plane-wave exposures. The finite-difference time-domain method is used for analyzing electromagnetic absorption and temperature elevation. The eyes in the anatomic models have average dimensions and weight. Computational results show that the ratio of maximum temperature in the lens to the eye-average SAR (named 'heating factor for the lens') is almost uniform (0.112-0.147 degrees C kg W(-1)) in the frequency region below 3 GHz. Above 3 GHz, this ratio increases gradually with an increase of frequency, which is attributed to the penetration depth of an electromagnetic wave. Particular attention is paid to the difference in the heating factor for the lens between this study and earlier works. Considering causes clarified in this study, compensated heating factors in all these studies are found to be in good agreement.
    Physics in Medicine and Biology 12/2007; 52(21):6389-99. · 2.70 Impact Factor
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    ABSTRACT: This paper computationally verifies the effect of anesthesia on temperature variations in the rabbit eye due to microwave energy. The main reason for this investigation is that our previous paper suggested a reduction in blood flow due to the administration of anesthesia, resulting in an overestimated temperature increase. However, no quantitative investigation has yet been conducted. The finite-difference time-domain (FDTD) method is used for calculating power absorption and temperature variation in rabbits. For this purpose, we used a computational rabbit phantom, which is comprised of 12 tissues (including 6 eye tissues) with a resolution of 1 mm. Thermal constants of the rabbit were derived by comparing measured and calculated temperatures. For intense microwave exposure to the rabbit eye, time courses of calculated and measured temperatures were in good agreement for cases both with and without the administration of anesthesia. The point to be stressed is that under anesthesia the thermoregulatory response was inactivated and blood flow and basal metabolism was reduced.
    Bioelectromagnetics 01/2007; 27(8):602-12. · 2.02 Impact Factor
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    ABSTRACT: This paper investigates the correlation between maximum temperature increases and peak spatial-average specific absorption rates (SARs), calculated by different average schemes and masses. For evaluating the effect of mass on the correlation properly, a three-dimensional Green's function is presented. From our computational investigation, no best average mass for peak spatial-average SAR exist from the aspect of the correlation with maximum temperature increase. This is attributed to the frequency dependent penetration depth of EM waves. Maximum temperature increase in the head including the pinna is reasonably correlated with peak spatial-average SARs for most average schemes and masses considered in this paper. Maximum temperature increase in the head only (excluding the pinna) is reasonably correlated with peak 10-g SARs for the average schemes considered in this paper. The rationale for this result is explained using the Green's function. The point to be stressed here is that the slope correlating them is largely dependent on the average scheme and mass. Additionally, good agreement is observed in the slopes obtained by using two head models, which have been developed at Osaka University and Nagoya Institute of Technology. However, weak correlation is observed for the brain, which is caused by the difference of the positions where peak SAR and maximum temperature increase appear. The 95th percentile values of the slope correlating maximum temperature increases in the head or brain and peak spatial-average SAR are quantified for different average schemes and masses
    IEEE Transactions on Electromagnetic Compatibility 09/2006; · 1.33 Impact Factor
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    Akimasa Hirata, Osamu Fujiwara, Toshiyuki Shiozawa
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    ABSTRACT: This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is throughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified.
    IEEE Transactions on Biomedical Engineering 09/2006; 53(8):1658-64. · 2.35 Impact Factor
  • T. Shiozawa, T. Muya, A. Hirata
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    ABSTRACT: The frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10% bandwidth around the center frequency 121 GHz
    IEEE Transactions on Plasma Science 07/2006; · 0.87 Impact Factor
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    ABSTRACT: This paper investigates the correlation between the peak specific absorption rate (SAR) and the maximum temperature increase in head models of adults and children due to a dipole antenna. Much attention is paid to the effect of variation of electrical and thermal constants on the correlation for the child models, since these constants of child tissues are different from those of adult tissues. For investigating these correlations thoroughly, a total of 1400 situations are considered for the following six models: 3-year-old child, 7-year-old child, and adult models developed at the Nagoya Institute of Technology and the Osaka the University. The numerical results are analyzed on the basis of statistics. We find that the maximum temperature increases in the head can be estimated linearly in terms of peak SAR averaged over 1- or 10-g of tissue. In particular, no clear difference is observed between the adult and child models in terms of the slopes correlating the maximum temperature increase with the peak SAR. Also, the effect of electrical and thermal constants of tissue on these correlation is found to be marginal. Further, we discuss possible maximum temperature increases in the head and brain for SAR limits prescribed in safety guidelines. For the adult model developed at the Osaka Univ., these are found to be 0.26degC and 0.10degC at the SAR value of 1.6 W/kg for 1-g cubic tissue and 0.59degC and 0.21degC at the SAR value of 2.0 W/kg for 10-g cubic tissue. Similarly, for the 3-year-old child model at Osaka Univ., these are 0.23degC and 0.11degC for the value of 1-g SAR and 0.53degC and 0.20degC for the value of 10-g SAR
    IEEE Transactions on Electromagnetic Compatibility 03/2006; · 1.33 Impact Factor
  • T. Shiozawa, T. Muya, A Hirata, Z. Kawasaki
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    ABSTRACT: The frequency-tunability for a Smith-Purcell free-electron laser in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10 % bandwidth around the center frequency 121 GHz.
    Microwave Conference, 2005 European; 11/2005
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    ABSTRACT: This paper presents maximum temperature increase in the head and brain with peak SAR calculated by different averaging schemes. For our computational investigations, it is found that maximum temperature increases in the head are well correlated with peak spatial-average SARs. However, the slope correlating them is largely dependent on the averaging scheme. Additionally, no clear difference is observed in the slope obtained using two head models. Possible maximum temperature increase in the brain for the SAR values is also quantified.
    Electromagnetic Compatibility, 2005. EMC 2005. 2005 International Symposium on; 09/2005
  • K. Kiminami, A. Hirata, Y. Horii, T. Shiozawa
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    ABSTRACT: This paper discusses the human body modeling for the design of a mobile terminal antenna at 400 MHz band. The effect of the human body inhomogeneity and shape on the radiation characteristics of the mobile terminal antenna is investigated thoroughly. In addition, the effect of the human arm on the antenna characteristics is also discussed. For this purpose, first, the radiation characteristics of a dipole antenna in the presence of an anatomically-based human body model and those for a homogeneous anthropomorphic model are compared. Next, the radiation characteristics for the anthropomorphic model and shape-simplified models are compared. The numerical and experimental investigations reveal that the effect of the inhomogeneity and shape of the human body on the antenna characteristics is not large from the viewpoint of antenna designs. On the other hand, the effect of human arm on them is larger than those due to the other factors.
    Journal of Electromagnetic Waves and Applications 03/2005; 19(5):671-687. · 1.40 Impact Factor
  • Journal of Electromagnetic Waves and Applications 03/2005; 19(3):401-411. · 1.40 Impact Factor
  • Shock Waves 03/2005; 19(3):401-411. · 0.60 Impact Factor
  • A. Hirata, S. Mitsuzono, T. Shiozawa
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    ABSTRACT: This work investigates the effect of the human head on the accuracy and depth of an adaptive nulling when the antenna array is implemented on a handset at 5.0-GHz band. Our numerical results show that the MUSIC spectrum obtained by the linear dipole array is largely affected by the coupling between the antenna and the head model. In particular, this effect is dependent on the separation between the array and the head. In order to suppress this effect, a metallic plate is inserted between the array and the head. The effectiveness of this proposal is demonstrated numerically.
    IEEE Antennas and Wireless Propagation Letters 01/2005; · 1.67 Impact Factor
  • K. Kiminami, A. Hirata, T. Shiozawa
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    ABSTRACT: This letter proposes a double-sided printed bow-tie antenna for ultra wide band (UWB) applications. The frequency band considered is 3.1-10.6 GHz, which has been approved by the Federal Communications Commission as a commercial UWB band. The proposed antenna has a return loss less than 10 dB, phase linearity, and gain flatness over the above frequency band.
    IEEE Antennas and Wireless Propagation Letters 01/2005; · 1.67 Impact Factor
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    ABSTRACT: This paper discusses the human head modeling for the design of handset antennas at 5GHz band. The effect of the human head heterogeneity and shape on the antenna characteristics is investigated thoroughly. In addition, an attempt is also made to realize a compact structure for the human head model. For this purpose, the radiation characteristics of a dipole antenna in the presence of several head models are compared. The numerical investigations reveal that the effect of the heterogeneity and shape of the human head model on the antenna characteristics at 5GHz band is marginal. Particularly, reasonable result can be obtained even for a model of rectangular parallelepiped with the dimensions (24 mm thickness × 120 mm × 120 mm). This volume is 96% smaller than the original realistic model.
    Journal of Electromagnetic Waves and Applications 01/2005; 19(3):401-411. · 1.40 Impact Factor
  • A. Hirata, T. Fujino, T. Shiozawa
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    ABSTRACT: This paper investigates the specific absorption rate (SAR) and temperature increase due to a body-mounted dipole antenna, attached to the neck, waist, and abdomen, in the 400 MHz and 900 MHz bands. As a main result, a strong correlation was observed between peak SAR and maximum temperature increase in the body, as is the case with EM wave exposures from handset antennas.
    Antennas and Propagation Society International Symposium, 2004. IEEE; 07/2004
  • A. Hirata, S. Mitsuzono, T. Shiozawa
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    ABSTRACT: The effect of the human head on the accuracy and depth of adaptive ing has been investigated. The frequency band considered was 5.0 GHz, which would be the most promising for the 4G mobile communications. Our numerical investigation shows that the MUSIC spectrum obtained by the linear dipole array is largely affected by the antenna-head coupling. In particular, this effect is dependent on the separation between the array and the head. In order to suppress it, a metallic plate was inserted between the array and the head. The effectiveness of this idea was demonstrated numerically.
    Antennas and Propagation Society International Symposium, 2004. IEEE; 07/2004
  • S. Kondoh, A. Hirata, T. Shiozawa
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    ABSTRACT: With the use of a generalized transfer-matrix method based on the mode-matching approach for waveguide step discontinuities, reflection properties of metallic waveguide gratings with rectangular grooves are investigated. A proper design for a compact and wide-band reflector grating which can support single-mode operation is also discussed. A waveguide grating with symmetrical and similar cross sections is shown to be of great significance for single-mode support and for constructing a compact reflector. In addition, it is found possible to obtain metallic waveguide gratings which satisfy all the specified requirements by properly adjusting only basic grating parameters.
    IEEE Transactions on Plasma Science 07/2004; · 0.87 Impact Factor
  • A. Hirata, T. Adachi, T. Shiozawa
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    ABSTRACT: A folded-loop antenna with a reflector for mobile handsets at the 2.0-GHz band is analyzed, taking the effect of the human head into account. The reflector is arranged between the human head and the driver. The width and height of the reflector are chosen to be slightly smaller and larger than those of the driver, respectively. Based upon numerical investigations, this antenna is found to enhance radiation efficiency by 20% and reduce peak specific absorption rates (SARs) averaged over 1 g and 10 g of tissues by 70%-85%. © Wiley Periodicals, Inc.
    Microwave and Optical Technology Letters 02/2004; 40(4):272-275. · 0.59 Impact Factor
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    ABSTRACT: The paper investigates the time constant of temperature increase in human head models due to a dipole antenna. The frequency band considered is from 900 MHz to 2.5 GHz. In order to discuss this problem thoroughly, hundreds of cases are considered: five frequency bands; two polarizations; two head models, with pressed and impressed ears; ten antenna feeding points. The results provide useful information in this field.
    01/2004;
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    ABSTRACT: We investigated the correlation between the peak SAR and the maximum temperature increase in the models of infants and adults for exposure to a dipole antenna. Numerical results show that the maximum temperature increases in the head and brain were reasonably proportional to the peak SAR in the corresponding regions. No clear difference in the correlation between the peak SAR and the maximum temperature increase was observed for infant and adult models. Additionally, the effect of the material constants on the correlation was at most 10%.
    Wireless Communication Technology, 2003. IEEE Topical Conference on; 11/2003