高橋 応明

MRI装置において,撮像するための電磁波の送信と,被検体から放出される信号の受信をするアンテナの設計には,体軸に垂直で均一な磁界を生成することが重要である.一般に,臨床で使用されている静磁界強度では,二つのリング状導体をエレメントと呼ばれる棒状の導体で支持する構造のアンテナ(バードケージコイル)が広く用いられている.このバードケージコイルは,エレメントの本数を増やすことで,より均一な磁界分布をコイル内で生成可能であることが知られている.近年のMRIシステムの高磁場化に伴う電磁波パルスの高周波化により,撮像時間の短縮や画質の向上が達成されている.一方で,被検体に吸収される電磁波エネルギーへの配慮が必要になってきており,MRI用アンテナを設計する際には,SARが低くなるように考慮することが重要である.そこで本論文では,バードケージコイル内に人体の電気的特性を模擬した生体等価電磁ファントムを配置して,エレメント本数を変えることによって,ファントム内の磁界分布とSAR分布がどのように変化するのか詳細に検討を行った.

This paper presents calculated specific absorption rate (SAR) dosimetry in 4 and 8 week Japanese pregnant-woman models exposed to plane waves over the frequency range of 10 MHz-1.5 GHz. Two types of 2 mm spatial-resolution pregnant-woman models comprised a woman model, which is similar to the average-sized Japanese adult female in height and weight, with a cubic (4 week) embryo or spheroidal (8 week) one. The averaged SAR in the embryos exposed to vertically and horizontally polarized plane waves at four kinds of propagation directions are calculated from 10 MHz to 1.5 GHz. The results indicate that the maximum average SAR in the embryos exposed to plane waves is lower than 0.08 W kg -1 when the incident power density is at the reference level of ICNIRP guideline for general public environment. © 2010 Institute of Physics and Engineering in Medicine.

This study computationally assessed the temperature elevations due to electromagnetic wave energy deposition during magnetic resonance imaging in non-pregnant and pregnant woman models. We used a thermal model with thermoregulatory response of the human body for our calculations. We also considered the effect of blood temperature variation on body core temperature. In a thermal equilibrium state, the temperature elevations in the intrinsic tissues of the woman and fetal tissues were 0.85 and 0.61 °C, respectively, at a whole-body averaged specific absorption rate of 2.0 W kg-1, which is the restriction value of the International Electrotechnical Commission for the normal operating mode. As predicted, these values are below the temperature elevation of 1.5 °C that is expected to be teratogenic. However, these values exceeded the recommended temperature elevation limit of 0.5 °C by the International Commission on Non-Ionizing Radiation Protection. We also assessed the irradiation time required for a temperature elevation of 0.5 °C at the aforementioned specific absorption rate. As a result, the calculated irradiation time was 40 min. © 2010 Institute of Physics and Engineering in Medicine.

This paper estimates separately the components of scattering waves generated in cylinder-body model for body area networks. For the evaluation, scattering field formulations in relation to uniform cylinder-and slab-body models are provided, and the reliability of the analyses is testified by the comparison with results computed by the finite-difference time-domain (FDTD) method. Creeping waves, cylinder leaky waves, and cylinder guided waves, which are created only in cylindrical structure, are extracted quantitatively by contrasting the scattering waves that are calculated with the two body models. In addition to the extracted waves, other components of scattering waves such as reflected waves, transmitted waves, surface waves, leaky waves, and guided waves also are examined. From evaluations with various operating frequencies and thicknesses of the body model, it is confirmed that reflected waves have the most influence on electrical characteristics of a source. Moreover creeping waves and cylinder leaky waves are generally dominant at the opposite side of the cylinder when a source is located near cylinder surface. Furthermore, the existence of creeping waves with low attenuation in the vicinity of cylinder surface is demonstrated by electric field intensities calculated by varying the observation point along cylinder axis.

This paper presents a field measurement of a simple antenna system mounted on a vehicle by utilizing a geostationary test satellite called Engineering Test Satellite VIII (ETS-VIII). Our developed antenna system is compact, lightweight, and promising for low-cost production. The antenna system is constructed by a 16-cm patch array antenna, which has simple satellite tracking that is controlled by a control unit as the vehicle's bearing is updated from a navigation system in real time. A Global Positioning System (GPS) module is utilized for the navigation system to provide accurate information of the vehicle's position and bearing during traveling. A control unit is provided as antenna-beam control and measured-data acquisition. We thoroughly examine the developed system in field measurements under open field areas and blockage areas in order to evaluate the propagation characteristics caused by utility poles, pedestrian overpasses, and vegetation-covered roads. In this measurement, the received signal power and the average bit error rate (BER) are simultaneously retrieved. Steadily received levels and average BER are satisfactorily attained during satellite tracking in open field areas. Moreover, the fade characteristics and average BER performance are also investigated during signal blockage. The results show that different environments give different degrees of attenuation, which affects the BER performance in terms of fade depth. Ultimately, our proposed antenna system can contribute to the design of future cost-effective mobile satellite communications.

This paper presents a simple antenna system for land vehicle communication aimed at Engineering Test Satellite-VIII (ETS-VIII) applications. The developed antenna system which designed for mounting in a vehicle is compact, light weight and offers simple satellite-tracking operation. This system uses a microstrip patch array antenna, which includes onboard-power divider and switching circuit for antenna feeding control, due to its low profile. A Global Positioning System (GPS) receiver is constructed to provide accurate information on the vehicle's position and bearing during traveling. The personal computer (PC) interfaces as the control unit and data acquisition, which were specifically designed for this application, allow the switching circuit control as well as the retrieving of the received power levels. In this research, the antenna system was firstly examined in an anechoic chamber for S parameter, axial ratio, and radiation characteristics. Satisfactory characteristics were obtained. As for beam-tracking of antenna, it was examined in the anechoic chamber with the gain above 5dBic and the axial ratio below 3dB. Moreover, good received power levels for tracking the ETS-VIII satellite in outdoor measurement, were confirmed.

This paper presents a realization of a simple antenna system for land vehicle satellite communication that is tested in experiments conducted on the Engineering Test Satellite-VIII (ETS-VIII). The developed antenna system which was mounted onto a vehicle roof is compact, light weight with simple satellite-tracking operation. In order to realize compact antennas, an onboard-power divider and switching circuit for antenna feeding control are mounted under the array antenna. A Global Positioning System (GPS) module is used to provide accurate information on the vehicle's position and bearing during travelling. A personal computer (PC) is used as the control unit and data logger, which was specifically designed for this application, allow the switching circuit control as well as the retrieving of the received power levels and error rate. The field tests reported in this paper mainly address the tracking performance of the proposed antenna system. Satisfactory results were obtained. Good received power levels and bit error rate (BER) for tracking the ETS-VIII satellite were confirmed. Furthermore, in order to grasp the environmental factors that impact the quality of land vehicle communications, we carefully captured data at obstacles such as buildings, foliages, utility poles and highway overpasses. The results showed blockage and shadowing was confirmed. Additionally, when the antenna was tested at the inclined-road for simple propagation characteristics in elevation direction, stable reception of the satellite signals was realized.

Magnetic resonance imaging (MRI) is a noninvasive imaging techniques used to visualize the inside of the human body based on nuclear magnetic resonance. Currently, RF coils that transmit high frequency and high power of electromagnetic (EM) wave pulses are being investigated to obtain high-quality images and to shorten the imaging time. Due to these approaches, the specific absorption rate (SAR) rise inside the human body has to be concerned during the imaging. Thus far, the SAR has been evaluated by calculating the EM fields inside the human body, and the safety of the human body has been reported. Meanwhile, according to the IEC standards, there are two methods to measure the total absorption energy of the human body model, although these methods cannot be used to evaluate detailed SAR distribution inside the body. It is important to comprehend detailed SAR distribution by measurement in order to consider reducing the SAR. In this paper, by use of the thermographic method, detailed SAR distribution inside the human head model was intended to measure employing birdcage coil for a 3.0-T MRI system. In the thermographic method, short time radiation and a sufficient temperature rise are required to obtain accurate SAR distribution. However, the effect of temperature diffusion inside the phantom caused by long time radiation depending on circumstances in the experiment must also be considered. In order to determine the temperature diffusion, temperature transition inside the phantom during the experiment was also measured by using a fluoroptic thermosensor. Then, multiplying the correction coefficients, which were calculated from the temperature transition by the measured SAR values, it was found that accurate SAR values could be obtained despite the long radiation time, and in addition, the measurement and calculation of SAR distribution were in good agreement. From these results, it has been verified that the proposed measurement method has a possibility of measuring detailed SAR distribution inside the phantom when any conventional RF coil is used. © 2009 IEEE.

本論文では,大地上人体がVHF帯の電磁波に曝露された際の影響をFDTD法を用いて定量的に評価することを目的とし,FDTD法における半無限大地の効率的なモデル化手法を検討した.FDTD法を用いて,半無限の媒質をモデル化するには,半無限媒質と整合をとったPML吸収条件を用いるのが一般的であるが,損失性媒質に対するPML吸収境界条件は計算コストの面で不利である.そこで本論文では,VHF帯においては大地の損失が小さいことに着目し,低損失媒質に対する表面インピーダンス条件を用いることで効率的な半無限大地のモデル化ができることを示す.解析対象は,地面に接触していない金属ワイヤ,及び人体の平均的な電気定数値をもつ損失性角柱とした.解析結果より,表面インピーダンス境界条件を用いた手法はPML吸収境界条件を用いた結果と同程度の精度を保ちながら大幅な計算時間の削減が可能であることが分かった.また,計算手法の妥当性は,モーメント法と比較することによって確認した.

心臓ペースメーカが動作プログラムの更新を行う際に,外部機器との間で通信を行うための体内植込み型アンテナを提案する.本論文では,板状素子と誘電体基板により構成され,人体正面方向において通信可能な板状逆Fアンテナ(Planar Inverted-F Antenna:PIFA)を設計した.まず,提案したアンテナを生体等価ファントム内に植え込んだモデルで数値解析を行い,MICS(Medical Implant Communications Services)バンドである402〜405MHzでのアンテナの動作を確認した.また,アンテナの植込み深さを変化させた際のアンテナ諸特性の変化について検討した.次に,ペースメーカから心臓に電気刺激を与えるリード線がアンテナ諸特性に及ぼす影響を確認するため,リード線をモデル化し,アンテナの給電位置を変更してアンテナ諸特性の数値解析を行った.その結果,リード線近傍に給電点が存在する場合を除き,顕著な影響は見られなかった.更に,実験により数値解析の妥当性の確認を行い,その結果より,提案したアンテナの有効性を明らかにした.

This paper presents the computational electromagnetic dosimetry inside an anatomically based pregnant woman models exposed to electromagnetic wave during magnetic resonance imaging. The two types of pregnant woman models corresponding to early gestation and 26 weeks gestation were used for this study. The specific absorption rate (SAR) in and around a fetus were calculated by radiated electromagnetic wave from highpass and lowpass birdcage coil. Numerical calculation results showed that high SAR region is observed at the body in the vicinity of gaps of the coil, and is related to concentrated electric field in the gaps of human body such as armpit and thigh. Moreover, it has confirmed that the SAR in the fetus is less than International Electrotechnical Commission limit of 10W/kg, when whole-body average SARs are 2W/kg and 4W/kg, which are the normal operating mode and first level controlled operating mode, respectively.

近年,RFID(Radio Frequency Identification)システムの急速な普及には目覚しいものがあり,物流管理,生産履歴管理ソリューションなど様々な分野で利用されている.本報告では,誘電体基板上にて対称構造の平面ダイポールアンテナにスリットを装荷することで,2周波共用のRFID用プリントアンテナを実現した.本アンテナの動作周波数は900MHz帯および2.45GHz帯の2つである.まず,アンテナの周波数特性を解析することで,提案したアンテナが所望の周波数帯域において動作することを確認した.そして,それぞれの周波数における電流分布を解析し,アンテナの動作原理を解明した.さらに,これらを踏まえて,放射パターンを考察した.

The portable radio terminal for business is usually hold in the vicinity of a human body, it is needed an attention for the specific absorption rate (SAR) in an abdomen. Therefore, in order to evaluate the SAR in the human body when wearing the portable radio terminals for business, the normal-mode helical antenna (NHA) with metallic case, which simulates the portable radio terminals for business at 150MHz, was modeled. In addition, the calculations of SAR distributions employing an NHA with metallic case in the vicinity of the tissue-equivalent phantom were compared with the measurements. As a result, the SAR distributions of calculated result agree well with those of measured result.

In recent years, a communications system, the Body Area Network, which uses the human body as a transmission path has attracted attention, and there is increasing expectation that it will be used more widely. However, there are still several points on the signal transmission mechanism of using the human body in this way that remain to be clarified, and there has been little research into the interaction of electromagnetic waves and the human body. Therefore, we used the Finite Difference Time Domain (FDTD) method to calculate the Efield distributions around simple and realistic models of the whole human body in free space with a weareble device. Moreover, E-field calculations were carried out when the positions of the body were changed. Our results show that using the simple homogeneous whole human body model is valid for the E-field calculation, and the dominant component of the E-field is normal to the body/air interface in all the positions that the human body assumes in daily life. Furthermore, in the state where the human body is shunted to the Earth ground, it was shown clearly that the E-field distribution is not mostly different from when a body is floating in free space. It can be concluded that these results provide useful information in improving the design of wearable devices.

In this paper, small sized arrays with a few elements are investigated. The antenna diameter is assumed to be less than 3λ_o. The focus of this paper is to compare the gain characteristics of a triangle arrangement with these of a uniform arrangement. The method of moments is used to calculating the gain characteristics. It is shown that the triangle arrangement is not always sufficient to obtain maximum gain for a small-sized antenna with only a few elements. Also, the type of antenna element used greatly influences the required number of elements and the element configuration.

In this paper, the authors propose a circularly polarized printed antenna combining a slot array antenna and a patch antenna, with dual-band operation. The proposed antenna has good isolation performance, is compact, and has simple configuration. This antenna is composed of two parts, a patch antenna (for Rx) on the top, and a slot array antenna (for Tx) on the bottom, respectively. The element layout is such that the lower radiation element is not hidden by the upper one for wide observation angle. Hence, both radiation elements can naturally radiate the targeted polarization. Both slot array and patch antenna are fed by electromagnetically coupled microstrip line feed. With such a configuration, it is possible to efficiently obtain good isolation characteristics for both frequency bands. Furthermore, this antenna can be easily composed and it is not necessary to use any feeding pin or via hole. The target of this antenna is mobile communications applications such as mobile satellite communications, base-station of wireless LAN, etc. Here, the design techniques are discussed and the numerical and experimental analyses are presented.

Previously, the authors studied biological tissue equivalent phantoms able to simulate the electrical constants of the human body in the 3- to 6-GHz band in a single composition ratio. Therefore, in this paper, we examined how to study the antenna characteristics using the phantom when extended to a bandwidth including 900 MHz to 3 GHz and 6 to 10 GHz and performed a quantitative study focusing on the electrical constants of the phantom. The result clearly showed hardly any effect of divergence of the phantom's electrical constants from the target values on the antenna input impedance, radiation efficiency, and radiation directivity. Therefore, in the entire ultra-wideband (UWB), this phantom can be accurately evaluated through antenna characteristic measurements and is clearly effective. Furthermore, differences due to the divergence of the phantom's electrical constants from the target values in the entire UWB bandwidth (3 to 10 GHz) are within +/- 3% for the average local specific absorption rate (SAR) inside the phantom caused by the electromagnetic wave energy radiated from the antenna. (c) 2007 Wiley Periodicals, Inc.

This paper presents a simple abdomen model of pregnant women and the evaluation of the specific absorption rate (SAR) inside the proposed model close to normal mode helical antennas (NHAs), which are replacing the portable radio terminals for business at 150MHz. First, dielectric properties of amniotic fluid and those of fetus of rabbit, which have about the same electrical properties as human, are measured. As a result, the conductivity of amniotic fluid is 1.8 times and that of fetus is 1.3 times higher than that of adult muscle at 150MHz. The result also suggests the modeling of pregnant women including the amniotic fluid and the fetus is necessary. Next, a simple abdomen model of pregnant women based on the measurements of magnetic resonance (MR) images of Japanese women in the late period of pregnancy is proposed. Finally, the SAR inside the proposed abdomen model close to 0.11λ and 0.18λ NHAs is calculated using the finite-difference time-domain (FDTD) method. As a result, we have confirmed that the 10-g average SAR in the fetus is sufficiently less than 2W/kg, when the output power of NHAs is 5W, which is the maximum power of portable radio terminals in Japan.

UWB技術を用いた通信は人体近傍において行われることが想定されるため,人体がアンテナ特性や伝送特性に与える影響を定量的に評価することが重要である.筆者らはこれまでに,人体近傍における高周波電磁界の評価を行うことを目的に,UWB通信で使用される周波数の全域(3〜10GHz)において,単一の組成比で±10%以内の差異で目標とする人体の電気定数を実現することができる広帯域生体等価固体ファントムを開発した.そこで本論文では,PDAに実装可能なUWB通信用アンテナの製作を行い,上記ファントムを用いてアンテナ特性の実験的評価を行った.その結果,3〜10GHzの広帯域において,UWB通信用アンテナの諸特性の計算と測定結果は良好に一致し,本ファントムが実際に広帯域特性をもつ通信端末の性能評価に適用可能であることが分かった.

技術試験衛星VIII型(ETS-VIII)の打上げ予定に伴い,S帯を用いた移動体衛星通信実験が計画されている.筆者らは移動局に搭載するアンテナとして,方位角3方向にビームを切り換える簡易衛星追尾型パッチアレーアンテナの開発を行っている.本アンテナは各素子への給電を制御回路によって電子的に"ON","OFF"させて衛星追尾を行う簡易な方式を用いているため,移相器やモータを必要とせず,システムの小型化や低価格化が期待できる.本論文では,簡易衛星追尾アンテナに適した給電回路を提案し,本回路を用いたアンテナのビーム切換特性の測定結果について述べる.まず,給電制御回路としてDP3T (Double Pole Three Throw)スイッチの開発を行った.次に,本回路をパッチアレーアンテナに搭載し,ビーム切換特性の測定を行った.その結果,本回路を用いることで,低い電力損でビーム切換が可能であることを確認し,本アンテナによって簡易に衛星追尾が行えることを示した.

近年の非接触ICカード/RFIDタグ等の急速な普及には目覚ましいものがあるが,使用されているアンテナは,システム全体の中で最も設計が難しいといっても過言ではない.これはアンテナの設計パラメータが,形状,材質,ICとのインピーダンス整合,通信エリアや各種規制等の遵守等々と非常に多岐にわたるためである.まず,このRFIDシステムには使用する周波数帯がいくつか用意されている.この中で13.56MHz帯を用いるシステムでは,アンテナが波長に対して非常に小形となることから微小アンテナの設計技術を必要とする.またUHF帯(860〜960MHz)やISM帯(2.45GHz帯)等では13.56MHz帯の場合とは異なり,通信エリアが電磁界の近傍界から遠方界にまで及ぶことから,その全域で動作させる必要があり,設計が困難となる.更に,RFIDを貼り付ける物質(金属や高誘電体等)によっても,アンテナ特性が大きく変化する.本論文では,これらの事例について,無線ICタグの設計法を述べる.

技術試験衛星VIII型(ETS-VIII)の打ち上げに伴い,S帯の周波数を利用した移動体衛星通信実験が計画されている.これまで筆者らは実験に用いる車載局用のアンテナとして,水平面内3方向にビームを切り換える簡易衛星追尾型パッチアレーアンテナ及び給電を制御するスイッチング回路の開発を行ってきた.本稿では,実際に電子スイッチと光ファイバジャイロを用いて,自動的にアンテナの方位角を検知し給電を制御する簡易衛星追尾の実証実験について報告する.実証実験において,電子スイッチと光ファイバジャイロを制御することで方位角3方向へのビーム切換が可能であり,本システムで簡易衛星追尾が行えることを確認した.

Intrabody communication using the human body as the transmission medium enables wireless communication without emitting radio waves into the surrounding environment. Experimental results on signal transmission gain in the frequency range from 1 to 1000 kHz have shown that the two-electrode arrangement, in which only one of the two electrodes of the transmitter and receiver are attached to the human body, has greater gain than the four-electrode arrangement, in which all four electrodes are attached to the human body. In addition, calculated gains based on four-terminal circuit models of two different electrode arrangements agree with empirical results. The validity of these four-terminal circuit models in the MHz frequency band was investigated using a 10.7-MHz intrabody sine-wave transmitter and receiver fabricated for this purpose. The results also indicate that the two-electrode arrangement is more suitable for high-speed intrabody communication devices than the four-electrode arrangement. Intrabody communication between two persons can be established by shaking hands, which have numerous practical applications, such as the exchange of personal data or e-cash among wearable PCs. © 2006 Elsevier B.V. All rights reserved.

The Japan Aerospace Exploration Agency (JAXA) plans to launch a geostationary satellite called Engineering Test Satellite VIII (ETS-VIII) in FY 2006. In this paper, a microstrip line array antenna, which has a very simple structure, is introduced to radiate a circularly polarized wave aiming at ETS-VIII applications. This antenna consists of a triangular conducting line with its vertexes rounded off, located above a ground plane, with a gap on one of its side to produce a circular polarization. The proposed antenna is analyzed by numerical simulations for a single element as well as for a three elements array configuration and the possibility of beam-switching in the azimuth space is experimentally confirmed in the latter case. It is found that by properly feeding the elements constituting the array antenna, for an elevation angle El=48° in Tokyo area, three beams are created in the conical-cut direction with a minimum gain more than 6.6dBic and an axial ratio less than 3dB.

In the past few years, there has been a focus on clean energy and the installation of solar cell modules on the walls of high-rise structures such as buildings. Solar cell modules embedded in window glass, which occupies a large portion of the walls of high-rise buildings, are being studied. However, solar cell modules easily reflect electromagnetic waves and the effect of electromagnetic wave interference cannot be ignored. Therefore, in this paper, we study a method for suppressing electromagnetic wave interference in the frequency bandwidth of terrestrial digital broadcasts when using solar cell modules embedded in window glass. By appropriately selecting the structure of the solar cell module and the shapes of the wires connecting solar cell pairs, at least 10-dB reflections can be suppressed in the frequency range from 470 MHz to 770 MHz of terrestrial digital broadcasts while preserving the lighting function of the window glass. © 2005 Wiley Periodicals, Inc.

筆者らはこれまでに, 単一の組成比で3〜6GHzの帯域において人体の電気定数を模擬することが可能な生体等価ファントムの検討を行ってきた.そこで本論文では, 900MHz〜3GHzと6〜10GHzを含む帯域に拡張した場合, 上記ファントムを用いたアンテナ諸特性の検討が可能かどうか, ファントムの電気定数に着目して定量的に検討を行った.その結果, アンテナ入力インピーダンス, 放射効率, 放射指向性には本ファントムの電気定数が目標値からずれてもあまり影響が現れないことが明らかになった.このことより, 本ファントムはUWB帯域の全域において, アンテナ諸特性の測定に関しては高精度な評価が可能であり, 有効であることが明らかになった.更に, アンテナから放射される電磁波エネルギーによるファントム内部での局所平均SARについても, UWB帯域の全域(3〜10GHz)においてファントムの電気定数が目標値からずれることによる差異は±3%以内に収まることが明らかになった.

本論文では, ETS-VIIIを利用した移動体衛星通信実験に用いる移動局用アンテナとして開発した2周波共用三角形パッチアレーアンテナと, 衛星通信実験へ向けて行われた衛星通信模擬実験について述べる.はじめに送受信の2周波共用と20dB以上のアイソレーション, 更に5dBic以上の利得を確保するために, 給電のON, OFFのみで方位角方向のみにビーム切換を行うアンテナについて, モーメント法を利用した数値計算と測定から検討した.次に実際に使用した場合における放射特性を把握するため, アンテナを実験車両の屋根に搭載し, 高さ32mの建物に設置した模擬衛星局からの電波を利用して衛星通信模擬実験を行った.実験によるデータの解析結果により, 車両搭載時においても給電のON, OFFのみによりビーム切換が可能であることを確認し, 本アンテナが有効であることを示した.

In this paper, the electrical constants of a biological tissue-equivalent agar-based solid phantom from 3.0 to 6.0 GHz are described. The developed phantom can reproduce the electrical constants of biological tissues from 3.0 to 6.0 GHz, and it is not necessary to change the phantom for each frequency band in the range of 3.0 to 6.0 GHz during the measurements. Moreover, adjustments to the dielectric constants of the phantom at 3.0, 3.8, 5.2, and 5.8 GHz are presented. The constants of this phantom can be adjusted mainly by using polyethylene powder and sodium chloride. The phantom can be used to evaluate the Specific Absorption Rate (SAR) as well as the antenna characteristics in the range of 3.0 to 6.0 GHz. Furthermore, the effect of the electrical constants of the phantom on the SAR is investigated. The investigation of SAR measurements is performed on the phantom at 5.2 GHz using the thermographic method. Calculations using the FD-TD method and the finite difference method based on the heat conduction equation are carried out in order to evaluate the thermal diffusion in the measurements using the thermographic method. The measured and calculated results are in good agreement. There is evidence that the thermal diffusion influences the SAR estimation at 5.2 GHz more than in a lower frequency range even though this method basically does not depend on the frequency.

Recently, wearable devices which use the human body as a transmission channel have been developed. However, there has been a lack of information related the transmission mechanism of such devices in the physical layer. Electro-magnetic communication trials using human body as transmission media have more than a decade's history. However, most of the researches have been conducted by researchers who just want to utilize the fact and practically no physical mechanisms have been researched until recently. Hence, in previous study, the authors proposed calculation models of the wearable transmitter and the receiver attached to the arm using the FDTD method. Moreover, the authors compared the calculated received signal levels to the measured ones by using a biological tissue-equivalent phantom. However, there was little analysis on each component of the propagated signal. In this paper, the authors clarified the transmission mechanism of the wearable device using the human body as a transmission channel from the view point of the interaction between electromagnetic wave and the human body. First, the authors focused their attention on measuring the each component of the propagated signal using a shielded loop antenna. From these results, the favorable direction of electrodes of the transmitter was proposed to use the human body as a transmission channel. As a result, longitudinal direction is effective for sending the signal to the receiver, compared to the transversal direction. Next, the authors investigated the dominant signal transmission channel, because the question of whether the dominant signal channel is in or around the arm had remained unsettled. To clear this question, the authors proposed the calculation model of an arm wearing the transmitter and receiver placed into a hole of a conductor plate. The electric field distribution and received signal voltage was investigated as a function of the gap between the hole of the conductor plate and the surface of the arm. The result indicated that the dominant signal transmission channel is not inside but the surface of the arm because signal seems to be distributed as a surface wave.

本論文では,FDTD法によるアンテナモデル化の適応性の向上を目的に,FDTDセルに対して斜めに給電された板状アンテナの解析法を提案し,自己補対アンテナ解析に適用することによって本手法の有効性を示す.

回路基板上の不要放射源推定を目的にMUSIC法を用いて有限距離において波源位置推定を行った.モードベクトルに球面波位相を考慮したものを用いることで,波源間距離がλという近距離において微小ダイポール,半波長ダイポール,ストリップラインなどについて放射部位推定が可能であることを示した.