伊藤 公一

Antennas and the propagation characteristics for body-area networks have become an active area of research. In this paper, a cavity slot antenna is proposed for onbody communications at 2.45 GHz. First, the antenna characteristics (input impedance, radiation pattern, and efficiency) are calculated by the finite-difference time-domain method. The results show that the proposed antenna has a relatively high efficiency of more than 50% even in the vicinity of the human body. Next, the onbody radio wave-propagation characteristics are investigated through numerical simulation and experimental measurements of the electric-field distributions around a phantom with a simplified shape of a human arm. Both sets of results are then compared and discussed. Finally, good agreement between the measured and the calculated results is confirmed.

Implantable devices have been investigated with great interest as communication tools. These implantable devices are embedded into the human or pet body. The vital information (such as temperature, blood pressure, cardiac beat, etc.) can be transmitted from implantable devices to the external equipment by use of a wireless communication link. Therefore, the research on the antenna for implantable devices (implanted antennas) is very important. This paper proposes an implanted H-shaped cavity slot antenna for short-range wireless communications. This type of antenna, which is designed to operate at the industrial-scientific-medical band (2.45 GHz), is investigated by using finite-difference time-domain calculation. We analyzed the performances of the proposed antenna which is embedded into the human body between the shoulder and the elbow. However, since the proposed antenna is too small to fabricate, a scale model is adopted for antenna measurements. Some characteristics of the scale model of the antenna are also calculated and measured by using the 2/3 muscle-equivalent phantom. The results show that the proposed antenna has promise for use in an implant.

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 150 MHz, 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.

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 10 W/kg, when whole-body average SARs are 2 W/kg and 4 W/kg, which are the normal operating mode and first level controlled operating mode, respectively.

本論文ではループアンテナを小形化する手法として導線部を折り返した構造をもつ折返し型方形ループアンテナを提案する.提案するアンテナは,方形ループアンテナを基本とした線状アンテナで,三次元的な占有空間を小さくする構造である.アンテナ全体として見たときに1波長ループアンテナと同等の電流分布になるように設計することで,アンテナを小形化しても8の字の放射形状を維持する.形状パラメータと電気特性の関係について述べ,その妥当性をアンテナを試作し,測定することにより確認する.

業務用無線端末は,主に胴体部に近接して使用されるため,電磁波の比吸収率(SAR)についての配慮が必要となる.また,国内において運用中の業務用無線端末に用いられている周波数帯では,携帯電話機に比べて波長の長い150MHz帯が主流であり,人体深部での電磁波曝露の作用が懸念される.本論文では,成人男性及び成人女性が業務用無線端末を装着した場合を想定して,高精細全身数値人体モデルの腰部近傍に150MHz帯きょう体付きノーマルモードヘリカルアンテナ(NHA)を配置した際の胴体内SAR評価を行った.ここでは,業務用無線端末を装着する位置の違いを考慮して,4通りのアンテナ配置における検討を行った.その結果,アンテナ位置は,全身平均SARに影響しないことを確認した.また,全身平均SAR及び10g平均SARは,国内の業務用無線端末の最大出力値である5Wで放射電力を規格化した場合において,管理環境の指針値(総務省・電波防護指針)より低いことが確認できた.

Since the diversification of the electromagnetic (EM) environment is spreading, it is essential to estimate the EM energy absorption rate [specific absorption rate (SAR)] of a pregnant woman's body and her fetus under various exposure situations. This paper presents the EM dosimetry in a pregnant woman in proximity to a mobile-phone terminal using the numerical model of a woman in her seventh month of pregnancy (composed of 56 organs, which includes the intrinsic organs of a pregnant woman) based on the high-resolution whole-body voxel model of a Japanese adult woman. It was found that. the SAR in the fetus strongly depends on the geometrical relationship between the fetus and the EM source, while the averaged SAR for the fetus is always lower than the RF safety guidelines under the exposure conditions investigated in this paper.

The numerical dosimetry of pregnant women is an important issue in electromagnetic-field safety. However, an anatomically realistic whole-body pregnant-woman model for electromagnetic dosimetry has not been developed. Therefore, we have developed a high-resolution whole-body model of pregnant women. A new fetus model including inherent tissues of pregnant women was constructed on the basis of abdominal magnetic resonance imaging data of a 26-week-pregnant woman. The whole-body pregnant-woman model was developed by combining the fetus model and a nonpregnant- woman model that was developed previously. The developed model consists of about 7 million cubical voxels of 2 mm size and is segmented into 56 tissues and organs. This pregnant-woman model is the first completely anatomically realistic voxel model that includes a realistic fetus model and enables a numerical simulation of electromagnetic dosimetry up to the gigahertz band. In this paper, we also present the basic specific absorption rate characteristics of the pregnant-woman model exposed to vertically and horizontally polarized electromagnetic waves from 10 MHz to 2 GHz.

The radiation characteristics of a monopole antenna that consists of one-half of a bow-tie dipole antenna, made of optically transparent conductive thin film and mounted above a ground plane, are investigated. The antenna's performance is measured for several films with different sheet resistivities. It is found that the gain lowering of the antenna caused by material resistance decreases from 4.4 dB to 0.2 dB at 2.4 GHz and the efficiency of the antenna increases from 46% to 93% at the same frequency, as the sheet resistivity decreases from 19.8 Omega/square to 1.3 Omega/square. The antenna is analyzed by the moment method. A wire-grid model with resistance loading on every discretized wire is applied. The analyzed results agree with the experimental values very well.

In recent years, wireless communications systems such as wireless LAN, Bluetooth, etc. are being rapidly adopted. As the antennas used in wireless communications systems are usually installed in small mobile devices, it is demanded that the volume should be small. In our research, we focus our attention on flexible printed circuits (FPCs) to meet the miniaturization demand. In this paper, we introduce a planar inverted F antenna (PIFA) suitable for TEEE802.11b/g and Bluetooth. The antenna is made of FPC. We measured the radiation pattern of the antenna when the antenna is successively curved and folded, and it is clear that its radiation performance does not vary much when the antenna is deformed. We analyzed the antenna by using the moment method.

In this paper, small sized arrays with a few elements are investigated. The antenna diameter is assumed to be less than 3 lambda(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.

Recently, wearable devices which use the human body as a transmission channel have been developed. However, there has been a lack of information related to the transmission mechanism of such devices in the physical layer. Electromagnetic communication trials using the human body as a transmission medium 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 this paper, the authors propose some calculation models of the human body equipped with the wearable devices by using the finite difference time domain (FDTD) method. Moreover, a biological tissue-equivalent solid phantom is utilized to show the validity of the calculation. From these investigations, the authors determine the transmission mechanism of the wearable devices using the human body as a transmission channel.

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.

Microwave energy is one of the heating sources used for thermal therapy of cancer. The thermal therapy means the hyperthermia and the coagulation therapy. In the hyperthermic treatment, the target tumor is heated up to 42-45 °C and in the coagulation therapy, it must be heated 60 °C or more to generate the tissue coagulation. In this manner, although therapeutic temperatures of both schemes are different, there are several similarities between them especially from the engineering aspects. Therefore, this paper describes the fundamental characteristics of microwave inside the biological tissue and two types of heating schemes for the hyperthermic treatments. In addition, the actual treatment by use of newly developed microwave antennas is introduced.

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 150 MHz. 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 ammotic fluid is 1.8 times and that of fetus is 1.3 times higher than that of adult muscle at 150 MHz. The result also suggests the modeling of pregnant women including the ammotic 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 0.11 lambda and 0.18 lambda 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 2 W/kg, when the output power of NHAs is 5 W, which is the maximum power of portable radio terminals in Japan.

A satellite-tracking left-handed circularly polarised triangular-patch array antenna has been developed to support the next generation of mobile satellite communications using Japanese Engineering Test Satellite VIII. The targeted minimum gain of the antenna was set to 5 dBic at an elevation of 48 degrees in the Tokyo area, for applications of about a hundred kbit/s data transfer. The antenna is composed of three equilateral triangular patches and fed by a dual-proximity feed. The influence of the array configuration on the characteristic of this antenna is investigated using a method of moments (MoM) approach and a simple point source model. The measurement of the fabricated antenna was then performed to confirm the simulation results. The result showed that the 10 mm distance between the patch apex to the centre of the array antenna satisfies the target. The frequency characteristic of the fabricated antenna is 0.7% shifted to the higher frequency, and the maximum gain is 0.9 dB lower than the simulation results. The result also shows that the characteristic of the patch array antenna satisfies the specification at elevation angle El=48 degrees, especially the 5 dBic gain coverage of the results covers the whole azimuth angle in a conical-cut plane at El = 48 degrees.

A left-handed circularly polarised (LHCP) triangular patch antenna is developed to support the next generation of mobile satellite communications using Engineering Test Satellite VIII (ETS-VIII). The targeted minimum gain of the antenna is set to 5 dBic for applications of a hundred kbps data transfer with an axial ratio less than 3dB for circular polarisation. A dual-proximity-coupled equilateral triangular patch antenna is proposed and simulated by the method of moments (MoM) for finite and infinite ground plane models to investigate the ground plane effect. Then measurements of the fabricated antenna are performed to confirm the simulation results. The measurement results show that the frequency characteristics of the fabricated antenna is 0.2% shifted to the higher frequency, and the maximum gain is 0.45 dB lower than the result of the finite ground plane model. Additionally, the simulation results show the ground plane size influences the antenna characteristics, especially the gain and axial ratio of the developed antenna.

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 degrees in Tokyo area, three beams are created in the conical-cut direction with a minimum gain more than 6.6 dBic and an axial ratio less than 3 dB.

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 per-formed 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.

In this research, a patch array antenna for mobile satellite communications aiming at ETS-VIII applications has been developed. The ground plane size effects on the antenna characteristics were investigated. Finite and infinite ground planes were analysed by the finite integration technique (FIT) for time domain analysis, the finite element method (FEM) and the method of moments (MoM) for spectral domain analysis. Then measurements of the fabricated antenna were performed to confirm the analysis results. It is clear that the frequency characteristics of the axial ratio are influenced by the variation in the ground plane size. When the ground plane size is increased, the edge-diffracted field causes tilting of the beam in the direction of low elevation angles and causes a decrease in the maximum gain and in the 3 dB beamwidth of axial ratio in the elevation plane. In the conical-cut direction, an increase in ground plane size induces a decrease in the 3 dB-beamwidth of axial ratio for FEM, but shows the opposite result for FIT and measurement. In addition, an increase in ground plane size also induces increases in maximum gain and its 6dBic-beamwidth along with a shift in the maximum gain in the direction of low azimuth angle. Copyright (c) 2004 John Wiley I Sons, Ltd.