高橋 応明

筆者らはこれまで,3GHz以上の周波数帯において,固体ファントムを用いたサ-モグラフィ法によるSAR測定の検討を行ってきた.その結果,3.8GHzや5.2GHzでは電磁波照射時間の経過に伴い熱移動の影響が大きくなることを確認した.また,電磁波照射時間の経過とともに温度上昇の測定誤差は小さくなることも確認している.そこで本論文では,電磁波照射によるある観測点での温度上昇の時間推移より算出した補正係数で,熱移動の影響を含む温度上昇分布に補正を行う提案をし,その有効性について確認を行った.その結果,照射電力が小さく熱移動の影響が大きな場合でも,この方法で補正することにより,測定誤差が十数%程度に抑えられることがわかった.

As the electromagnetic (EM) environment is becoming increasingly diverse, it is essential to estimate specific absorption rates (SARs) and temperature elevations of pregnant females and their fetuses under various exposure situations. This study presents calculated SARs and temperature elevations in a fetus exposed to EM waves. The calculations involved numerical models for the anatomical structures of a pregnant Japanese woman at gestational stages of 13, 18, and 26 weeks; the EM source was a wireless portable terminal placed close to the abdomen of the pregnant female model. The results indicate that fetal SARs and temperature elevations are closely related to the position of the fetus relative to the EM source. We also found that, although the fetal SAR caused by a half-wavelength dipole antenna is sometimes comparable to or slightly more than the International Commission Non-Ionizing Radiation Protection guidelines, it is lower than the guideline level in more realistic situations, such as when a planar inverted-F antenna is used. Furthermore, temperature elevations were significantly below the threshold set to prevent the child from being born with developmental disabilities.

In recent years, magnetic resonance imaging (MRI) systems that operate up to under 3 T are being used in clinical practice in Japan. In order to achieve the requirements of higher image quality and shorter imaging times, devices that utilize high magnetic fields (> 3 T) and high power electromagnetic (EM) wave pulses have been developed. The rise of the static magnetic field is proportional to the increase of the EM wave frequency which raises the issue of variation in capacitance used in the radio frequency (RF) coil for MRI system. In addition, increasing power causes problems of withstanding voltage and these approaches leads to generation of non-uniform magnetic field inside the RF coil. Therefore, we proposed a birdcage coil without the use of lumped circuit elements for MRI systems in previous study. However, it is difficult to fabricate this birdcage coil. Hence, simply-structured birdcage coil with no lumped circuit elements is desired. In this paper, we propose a simply-structured birdcage coil with no lumped circuit elements for a 4 T MRI system. In addition, the authors investigated the input impedance and magnetic field distribution of the proposed coil by FDTD calculations and measurements. The results confirm that the proposed birdcage coil matches the performance of the conventional birdcage coil which includes several capacitors.

In recent years, there has been rapid developments in radio-frequency identification (RFID) systems, and their industrial applications include logistics management, automatic object identification, access and parking management, etc. Moreover, RFID systems have also been introduced for the management of medical instruments in medical applications to improve the quality of medical services. In recent years, the combination of such a system with a biological monitoring system through permanent implantation in the human body has been suggested to reduce malpractice events and ameliorate the patient suffering. This paper presents an implantable RFID tag antenna design that can match the conjugate impedance of most integrated circuit (IC) chips (9.3-j55.2Ω at 2.45GHz. The proposed antenna can be injected into the human body through a biological syringe, owing to its compact size of 9.3mm × 1.0mm × 1.0mm. The input impedance, transmission coefficient, and received power are simulated by a finite element method (FEM). A three-layered phantom is used to confirm antenna performance.

As the electromagnetic (EM) environment becomes increasingly diverse, it is essential to evaluate exposures to EM waves for pregnant females and their fetuses. Therefore, we have determined the maternal and fetal specific absorption rates (SARs) of pregnant females at the 13th, 18th, and 26th gestational weeks using a high-definition numerical model of a flip phone in close proximity to the pregnant female’s abdomen. The results indicate that the difference between the simple EM source and the realictic one in the maternal and fetal SARs is within 30% in this case. Moreover, all calculated SARs were below the international safety guidelines.

Recently, the wireless power transmission (WPT) system is expected to employ as a means to transmit power to capsular endoscope diagnosing the digestive organs. In order to increase transmission efficiency, in this study, we proposed a transmitting spiral antenna which can transmit adequate power to the capsular endoscope with being independent of its position and direction. In this paper, we discussed the power transmission efficiency and SAR on human body by means of FDTD method and experimentation.

MIMO techniques using multiple antennas for improving communication capacity per unit frequency have been introduced. However, when multiple antennas are arranged in close proximity, the throughput is reduced because of the strong coupling between antennas, which causes low antenna efficiency. In this paper, to solve this problem, we propose a new decoupling method that uses a branch shape element instead of a susceptance circuit between antennas. A two-element MIMO antenna array in close proximity that uses this proposed method is presented. The coupling value S₁₂ and matching value S₁₁ of the S-parameters can be obtained at less than −10 dB in this MIMO antenna array.

本論文では,ベッドに横になっている被介護者に対し,RFID技術を用いた2種類の排尿検知システムを提案する.まず,ハンディリーダを用いた簡易排尿検知システムについて説明する.更に,リーダを据え置くことで,リアルタイムで紙オムツの吸収限界を検知するシステムを提案する.このRFIDシステムを用いた排尿検知において,アンテナの果たす役割は非常に大きい.本システム実現のために,それぞれのアンテナを設計し,数値シミュレーションと実験によりシステムの有用性を評価した.検証の結果,設計したアンテナを用いれば,提案するどちらのシステムでも排尿検知が行えることを示した.

ワイヤレス分野の中で期待されている分野の一つにボディエリアネットワーク(BAN)がある.本論文では,BANにおけるアンテナの技術的な課題について報告するとともに,実際の検討例として2GHz帯のOn-body用アンテナ,2.45GHz帯のIn-body用インプランタブルアンテナについて報告する.BAN用アンテナを設計するには,On-bodyでは人体方向に放射しないアンテナを用いること,In-bodyでは周囲の組織構造を模擬して設計する必要があることを示す.

近年,人体近傍での使用を前提とした電磁波技術を応用した機器の普及に伴い,それらから発生する電磁波と人体との相互作用を定量的かつ客観的に評価する必要性が高まってきている.このような相互作用を定量的に評価するためには,人体を用いて実験的に検討を行うことは困難である.そこで,数値モデルを用いたシミュレーションや生体組織と電気的特性(比誘電率,導電率)が等価なファントムが用いられている.ファントムに関する研究は,様々な研究機関で盛んに行われており,多種多様なファントムが開発されている.しかしながら,これらのファントムは,VHF(Very High Frequency)帯以上の周波数における電気的特性を模擬したものが大半を占めており,HF (High Frequency)帯以下の周波数用ファントムに関する検討はほとんどない.そこで本研究では,アルミニウム粉末と塩化ナトリウムを脱イオン水に添加したファントムを作製し,電気定数を測定した.その結果,アルミニウム粉末と塩化ナトリウムを添加する量を調整することにより,13.56MHzにおいて筋肉と電気的に等価であるファントムを開発することができた.

近年の無線端末では,映像等の大容量データを通信すべく,スループット向上が求められ,アンテナを複数使用するMIMO (Multiple-Input Multiple-Output)技術が導入されている.複数のMIMO用アンテナ素子を1箇所に近接配置できれば,アンテナの占有体積を削減できるとともに,アンテナへのRF線路による伝送損低減にも有利である.しかし,アンテナ間の結合による放射効率の劣化や,相関係数上昇によるスループットの減少が課題となる.この対策として,2素子モノポールアンテナの給電点間にインダクタとキャパシタの並列回路を配置することで2周波数での低結合化を行う手法が提案されている.しかし,LTEに代表されるセルラシステムではより多くの周波数帯への対応が必要であり,より多周波数に対応した低結合化手法が必要となっている.本論文では,アンテナ素子の構造を分岐形状とすることで,アンテナ素子のアドミタンスを最適化し,給電点間に配置する低結合回路の部品点数を増加させずに組み合わせることで,3周波数での低結合化を報告している.また本手法により,3周波数でのアンテナ効率上昇及び相関係数低下を,電磁界シミュレーションと実測により確認したので報告する.

Wireless power transmission is being investigated as a means to operate tiny medical equipments such as capsular endoscope that exists for a long time in the body. In this paper, we examine the wireless power transmission to a capsular endoscope by microwave as a new approach, in order to show its usability for medical applications. We propose power receiving antennas inside the endoscope, transmitting antennas and the transmitting system that operates at 433.92 MHz. We calculate maximum received power in the intestines by using these antennas. The results show that adequate power can be well received at 433.92 MHz. © 2013 American Scientific Publishers.

Radio frequency identification (RFID) system has been expected to be expanded in new fields. This paper shows a sensing system for urination by embedding an RFID tag into a paper diaper. The urination could be checked by change of the antenna characteristics. It could be possible to reduce physical and mental strain of both patients and their care personnel. In order to detect the urination, the RFID antenna was designed and the characteristics of the antenna were calculated. In addition, the antenna characteristics were measured with a phantom. As the result, urination considerably changes the antenna characteristics and that the system can be used to detect the urination.

Implantable devices have been continually anticipated as a future tool for in-body wireless communication because of their potential to replace cable connectivity with biological telemetry monitoring. This paper presents an implanted compact folded antenna of 20.3 mm 0.8 mm 0.8 mm that is designed to operate at one of the UHF bands (0.951?0.956 GHz). The measurement is implemented with an equivalent human phantom such as layered phantom representing the human arm. When the proposed antenna is implanted into a human arm, it has a maximum antenna gain of 23.5 dBi and wireless communication is viable because the margin exceeds 20 dB, according to link budget calculations. © 2012 IEEE.

An in-body wireless communication system has attracted increasing attention because it can replace the connectivity of biological telemetry monitoring. However, the human body is a very complex environment (lossy, dispersive, and inhomogeneous) and affects the electromagnetic (EM) wave in the near field. Moreover, the entire human geometry affects the radiation pattern in the far field. This communication presents the behavior of the EM wave in the near and far fields at 2.45 GHz when a dipole antenna (used as an implantable antenna) is embedded in the vicinity of the clavicle, upper arm, lower arm, and hand of a human body. The effect on the electric field and radiation performance is simulated by the finite-difference time-domain method. By introducing a three-layered phantom, the antenna performance is confirmed. Moreover, the measured and simulated results are in good agreement with each other. The information derived from this study can be used in the evaluation of the link budget of in-body wireless communication. © 1963-2012 IEEE.

The physical channels establishing intrabody communications were first treated as capacitive circuits by Zimmerman. In Zimmerman's model, the human body is approximated as a perfect conductor. The equivalent-circuit parameters of the perfect conductor models can be strictly obtained based on electrostatic analyses however, the perfect conductor models cannot be applied if conduction currents inside the human body are not negligible. In the present paper, a theory of the equivalent circuit for lossy conductors is described, and the physical mechanism of the communication channels inducing conduction currents inside the human body is addressed. © 1963-2012 IEEE.

This paper introduces a radio frequency identification (RFID) tag for urination detection. The proposed tag is embedded into paper diapers in order to detect the patient's urination immediately. For this tag, we designed an RFID tag antenna at 950MHz, which matches the impedance of the associated integrated circuit (IC) chip. In addition, we calculate the antenna characteristics and measure the reflection coefficient (S₁₁) and radiation pattern of the antenna. The results show that this system can be used to detect urination.

Hyperthermia is one of the modalities for cancer treatment, utilizing the difference of thermal sensitivity between tumor and normal tissue. Interstitial microwave hyperthermia is one of the heating schemes and it is applied to a localized tumor. In the treatments, heating pattern control around antennas are important, especially for the treatment in and around critical organs. This paper introduces a coaxial-dipole antenna, which is one of the thin microwave antennas and can generate a controllable heating pattern. Moreover, generations of an arbitrary shape heating patterns by an array applicator composed of four coaxial-dipole antennas are described.

Radio frequency identification (RFID) system is developing quickly in recent years, and its industry including logistics management, automatic object identification, etc. Moreover, it is suggested to combine with in-body wireless communication to reduce medical error and receive the patients’ information without connecting cable lines in hospitals. In this paper, we proposed an implantable RFID antenna which is designed to operate at 2.4GHz (2.4-2.485GHz) and matched a IC chip with conjugate impedance of 9.3-j55.2Ω. The good impedance matching can be obtained by adding loop structure, and moreover, miniaturization of antenna is achieved by folded structure. Therefore, the whole size of proposed antenna with glass coating is only 9.3mm × 1.0mm × 1.0mm. The impedance characteristic of implantable RFID antenna is simulated by use of finite element method (FEM) and the experiment is implemented with three-layered phantom which represents human upper arm.

In recent years, Radio Frequency Identification (RFID) systems are expected to be used in the medical field. Therefore we have come to suggest a simple urination detection system by the RFID system. In our presented system a tag is embedded into a diaper worn by a care-receiver and the care-personnel bring a reader close to the tag. Thus, in a dry diaper, the tag can communicate with the reader. However, in a wet diaper, the presented tag cannot communicate with the reader, because the characteristics of the tag antenna are changed by urination. So urination is detected by weather the presented tag can communicate with the reader or not. In this paper, we have designed the tag antenna and analyzed it by numerical calculations. In addition, we fabricated the tag and measured it in a real situation. As a result the presented system can be applied in urination detection.

In-body wireless communication has attracted increasing attention because it can not only be used in medical application but also be combined with wireless communication to replace the existing connectivity in biological telemetry monitoring [1]. Therefore, it is possible to integrate radio frequency identification (RFID) system into a brand-new device [2]. However, it has been very difficult to combine them due to high lossy of human body. In this paper, an implantable tag antenna which is designed to match an integrated circuit (IC) chip of 9.3-j55.2Ω [3] is proposed and realized in experiment. The dimensions of proposed antenna is 15.75mm × 4mm. The impedance characteristic of proposed antenna is analyzed by finite-difference time-domain (FDTD) method. By introducing the three-layered phantom, the measurements of impedance characteristic is implemented; moreover, the maximum read range of 1.3cm is confirmed by a handy reader.

Evaluation of the interaction between the electromagnetic waves, radiated by mobile communications, broadcast, medical applications, and so forth, and the human body is indispensable. The interaction is generally estimated by numerical calculations and experimental evaluations. In these evaluations, biological tissue-equivalent phantoms, which are adjusted to have the same dielectric constants as human tissue, are generally used. Until now, various investigations have studied the phantoms. However, most of these studies have focused on the phantom for the very high frequency band (VHF) and above. Therefore, in this paper, we propose a multi-layered (muscle, fat and skin) tissue-equivalent phantom in the high frequency (HF) band.

A novel dual-mode antenna for on-body and off-body communications is proposed. In on-body mode, the antenna is similar to a pair of metal electrodes operating at 10MHz and in off-body mode, with an L-shaped slit embedded, the antenna can cover the 2.45GHz ISM band. Measured results, including received voltage at 10MHz, reflection coefficient and radiation patterns in the 2.45GHz ISM band are presented to validate the proposed antenna. © 2012 The Institution of Engineering and Technology.

The research on body-centric wireless communications (BCWCs) is becoming very hot because of numerous applications, especially the application of E-health systems. Therefore, a small multi-band and low-profile planar inverted-F antenna (PIFA) with tuning function is presented for BCWCs in this paper. In order to achieve multi-band operation, there are two branches in the antenna: the longer branch low frequency band (950-956MHz), and the shorter branch with a varactor diode embedded for high frequency bands. By supplying different DC voltages, the capacitance of the varactor diode varies, so the resonant frequency can be tuned without changing the dimension of the antenna. While the bias is set at 6V and 14V, WiMAX and ISM bands can be covered, respectively. From the radiation patterns, at 950MHz, the proposed antenna is suitable for on-body communications, and in WiMAX and ISM bands, they are suitable for both on-body and off-body communications.

Although the effect of electromagnetic interference on an implanted cardiac pacemaker due to a nearby mobile phone has been investigated, there have been few studies on the enhancement of the specific absorption rate (SAR) around an implanted cardiac pacemaker due to a nearby mobile phone. In this study, the SAR distribution around a pacemaker model embedded in a parallelepiped torso phantom when a mobile phone was nearby was numerically calculated and experimentally measured. The results of both investigations showed a characteristic SAR distribution. The system presented can be used to estimate the effects of electromagnetic interference on implanted electric circuits and thus could lead to the development of guidelines for the safe use of mobile radio terminals near people with medical implants.

Mutual coupling is a critical problem in the design of MIMOantennas because it deteriorates the performance ofMIMO systems, which not only affects the antenna efficiency but also influences the correlation. Therefore, in this paper, using parasitic elements to reduce mutual coupling is studied. By adding parasitic elements a double-coupling path is introduced and it can create a reverse coupling to reduce mutual coupling. As an example, a dual-slot-element antenna with parasiticmonopoles formobile terminals is described. The discussion on channel capacity shows that the antenna can be considered as a good candidate for MIMO systems. Furthermore, based on the study of current distributions, it is concluded that the technique is sensitive to relative positions between parasitic elements, and relative positions between active element and parasitic element. Finally, we also extend the technique to a tri-element antenna. © 2011 IEEE.

人体周辺に電界を励起して通信を行う,人体通信の物理チャネルは,考案当初から,容量結合の回路モデルとして扱われてきた.筆者らはこれまでに,通信チャネルの完全な等価回路を,導体電位に関する境界値問題を解くことで導出を行った.その結果,送受信機が共に接地されていないウェアラブル機器の場合,送受信電極間の直接結合が無視できず,したがって送受信機の装着位置と人体の姿勢変化を考慮しなければならないことが明らかとなった.しかしながら,上記の検討では,議論の普遍性のため人体を導体球で模擬しており,腕の動きのような姿勢変化及び大地の存在は考慮していなかった.そこで本論文では,より実際の人体に近い人体モデルを用いて,等価回路パラメータ及び送受信機間の信号伝送特性に対する姿勢及び大地の影響について検討を行った.その結果,人体腕部の動きによる影響が,送受信機の装着位置により異なることを確認した.また,人体と大地間の距離が変わっても人体の静電容量が大きく変化せず,信号伝送特性もほとんど変化しないことが明らかとなった.

我々は, 胆管部腫瘍の治療法としてマイクロ波を用いた腔内温熱療法の研究を行ってきた. この治療法では, 内視鏡の鉗子口を利用することで, ファーター乳頭から胆管までアンテナを非侵襲的に誘導し, 患部の局所加温を行う. ところで, 近年では胆管部腫瘍が外科的切除不可能である場合に, メタルステントを胆管内に留置するケースが増えている. しかしながら, 胆管にメタルステントが留置された状態での効果的なマイクロ波温熱治療法は確立されていない. また, 筆者らは, メタルステントが温熱治療に影響を及ぼすことを確認している. そこで本研究では, 胆管部腫瘍に対するマイクロ波温熱治療と併用可能な胆管ステントの開発を行った. 提案したステントは, 周囲に存在する腫瘍を広範囲に加温することを目的として, 金属とプラスチックから構成されている. この治療では, 内視鏡用マイクロ波同軸プローブから照射された電磁波が提案したステントから外部に漏洩することで, ステント周囲のマイクロ波加温を実現した. 本論文では, FDTD (Finite-Difference Time-Domain) 法を用いた電磁界解析と生体等価ファントムを用いた加温実験を行った結果より, 提案したステントはマイクロ波温熱治療と併用可能であることを示した.

Body-centric wireless communications (BCWCs) have received a great deal of attention recently. This communication proposes a compact planar inverted-F antenna (PIFA) operating at 2.45 GHz for on-body communications. Two shorting structures and a folded ground plane are used to improve the impedance matching and decrease the size of the proposed antenna. As a result, the proposed antenna is low-profile and compact in size, and it does not change significantly when in close proximity to the human body. This communication studies the characteristics of the proposed antenna close to the arm phantom by simulation and experiments. Both simulated and measured results are in good agreement. © 1963-2012 IEEE.

In recent years, body-centric wireless communications have been studied because they have potential to improve the qualities of various kinds of applications. Since the prospective frequencies for the body-centric wireless communications are in an extremely wide range from megahertz to gigahertz, an objective idea on how to select a right frequency band for individual applications is required. However, few publications have tackled this need. In this paper, the frequency dependence of the communication channels in the range of 3 MHz to 3 GHz is assessed based on numerical analyses.

The miniaturization of electronic devices is leading to the creation of body-centric wireless communications, in which wireless devices are attached to human body. However, the human body environment is often uninviting for wireless signals owing to the mutual influence between the human body and wireless devices' antennas, namely wearable antennas. Therefore, wearable antennas need to be carefully designed. In this paper, a small wearable antenna with folded ground at 2.4GHz is proposed. The folded ground has two effects: one is to improve efficiency and the other is to enhance bandwidth. When the antenna is very close to human body, it has an efficiency of 50.7% and a wide operation bandwidth of 130MHz.

Physical channels of the intra-body communications, in which communications are performed by exciting electric field around the human body, have been treated as a capacitive circuit from the beginning of the development. Although the circuit-like understanding of the channels are helpful to design devices and systems, there is a problem that the results may be invalid if the circuit parameters are incorrectly estimated. In the present study, the values of the circuit parameters are properly derived by solving a boundary value problem of electric potentials of the conductors. Furthermore, approximate models which are appropriate for cases that some of the conductors are grounded are investigated.

近年の情報端末では,音楽,映像等の大容量データを安定して通信すべく,通信品質の確保,通信容量の向上が求められており,対策としてMIMO(Multiple-Input Multiple-Output)技術の導入が検討されている.MIMOでは,複数のアンテナが必要になるが,これらを近接配置し,1箇所に集約できれば,素子配置に用いる体積減少によるデザイン性向上や,アンテナから無線部へのRF線路引回し削減による伝搬損低減のメリットが得られる.しかし,強い素子間結合によるアンテナ効率の減少,高い相関係数によるスループット減少の懸念がある.本論文では,近接配置したMIMOアンテナの結合除去方法として,所望周波数でのアンテナ素子のインピーダンスに依存せずに,複数周波数同時に結合を低減する手法を提案した.基礎検討として,2素子モノポールアンテナ及び2素子メアンダアンテナを近接配置したモデルで検討を行い,低結合回路をアンテナ給電点間に配置することで,所望2周波数を同時に低結合化可能であることを示した.またこの対策により,アンテナ効率向上,相関係数の低減が得られることを確認した.

Ultra Wide Band(UWB)は,近距離,低消費電力,大容量通信という他の通信システムにはない特徴をもっており,ホームネットワーク,ワイヤレスUniversal Serial Bus(USB)など様々な分野での利用が検討されている.今後は,Wireless Body Area Network(WBAN)の標準化に伴い,人体近傍での利用が予想される.そこで筆者らは,日本国内において,UWB通信に認可されている7.25〜10.25GHzで動作する人体腕部装着型の広帯域アンテナを提案した.本論文では,提案したアンテナの入力特性を解析し,所望の帯域内でVoltage Standing Wave Ratio(VSWR)が2.0以下となることを確認した.次に,アンテナの特徴を近傍界・遠方界の両面から考察すべく,電界強度分布と放射パターンを検討した.その結果,本アンテナは腕先端方向への通信に有利なこと,発生する電界は人体に垂直な成分が支配的であることを確認した.以上のことから,本論文で提案したアンテナは,人体腕部装着型UWBアンテナとして,有用であることが分かった.

地上アナログテレビジョン放送が2011年7月に終了し,ディジタル放送に完全移行する.総務省情報通信審議会では,空き周波数帯の170〜205MHzを災害対策,救援用の利用を想定した公共,公益分野におけるVHF帯ブロードバンド移動通信システムに割り当てることが適当であると報告した.本論文では,VHF帯ブロードバンド移動通信システム用アンテナの開発を目的として,所望の周波数帯で動作し,きょう体に内蔵可能なアンテナを提案した.また,人体近傍におけるアンテナの諸特性を,数値解析及び測定によって検討した.

近年,次世代の無線通信システムの一つとして,人体に取り付けた端末(ウェアラブルデバイス)によって通信を行うWBAN(Wireless Body Area Network)が注目されている.より高性能なウェアラブルデバイスを実現するためには,人体近傍に配置するアンテナの形状や人体近傍の電波伝搬の問題を明らかにすることが重要である.本論文では,人体近傍における電波伝搬機構を解明するために,人体を模擬した無限長誘電体円柱の近傍に配置したダイポールアンテナから電磁波が入射する場合の散乱電界の厳密解を導出し,電界分布を計算した.次に,円柱近傍に配置した送受信アンテナ間の伝達係数を求め,生体等価ファントム及び実人体を用いた測定結果と比較した.更に,UWBバンドにおけるUWB-IR方式とISMバンドの一つである915MHz帯においてBPSK方式を用いたときのBERシミュレーションを行った.以上の結果より,ほとんどの場合について円柱があることによりBER特性が良くなることを示し,特に受信アンテナがφ=90°の位置にあるときには円柱による散乱界の寄与によりBER特性が大幅に改善することを示した.

携帯端末のアンテナ特性は,実使用状況において使用者の手や胴体の影響を受けることが知られている.そこで,携帯端末用アンテナを設計する際には,手がアンテナ特性に与える影響を考慮する必要がある.携帯端末を使用する際には,手のなし得る形状は,当然のことながら一定ではない.本研究では,任意に形状を変化させることができる手ファントムを作製した.作製した手ファントムの有用性を示すために,手ファントムと実際の手にアンテナを握らせた際のアンテナの入力特性の測定結果を比較し,数値計算により測定結果の妥当性を確認した.その結果,実際の手によるアンテナ特性への影響を評価する際に,作製した手ファントムを用いることの有用性を示した.

筆者らは,呼吸検出用ドップラーレーダの性能を評価するため,人体の腹部運動を模擬したダイナミックファントムを開発した.また,ダイナミックファントムと人体の測定によって得られる出力波形を比較することで,ダイナミックファントムの妥当性を示した.

Wireless power transmission is being investigated as a means to operate tiny medical devices such as the capsular endoscope, which is able to exist for a long period during diagnostic procedures within the body. In this paper, we examine the wireless power transmission to a capsular endoscope by electromagnetic waves to show its usability for medical applications. A modified helical antenna inside the endoscope is proposed as a power receiving antenna, operating at 915MHz. By calculating a maximum received power in the stomach using such antenna, the results show that adequate power can be well received.

胆管癌に対する治療方法の一つとして, 内視鏡とマイクロ波アンテナを併用した温熱療法が挙げられる. この治療では, 内視鏡鉗子口を利用することによって, ファーター乳頭から胆管までアンテナを非侵襲で誘導し, 患部の局所加温を行う. アンテナは柔軟性のある同軸ケーブルによって製作されており, 先端部に設置されたスロット部からマイクロ波エネルギーが照射される. 筆者らはこれまで, 摘出臓器を利用してアンテナの加温性能を評価してきた. そこで, 本論文では, アンテナの臨床使用に向けて, その効果や安全性を検証するために, ブタを用いた動物実験を実施し, アンテナの操作性や堅牢性に加え, 血流存在下において胆管部の組織を凝固させることなく42°Cまで上昇できるか否かを検証した. 本実験では, アンテナを十二指腸から胆管に向かって侵襲的に刺入し, その後, スロット部と温度測定点が離れすぎないように, X線画像によってアンテナと温度センサの位置を調整した. そして, 動物実験の結果, アンテナへの入力電力を15 W, マイクロ波の給電間隔をオン : 20 s, オフ : 5 sとした際に, 胆管部の組織を凝固させることなく30分間42°Cに保つことができた. なお, 実験終了後にスロット部から温度測定点までの距離を算出したところ, 4.8 mm離れていたことが分かった. さらに, この間アンテナは故障することなく正常に動作したため, アンテナは温熱療法に利用可能であると考えられる. また, 電磁界解析および温度解析を行ったところ, 血液流量率を2.33×10^-5 m³/kg•sとしたとき, 解析結果が実験結果と概ね一致した. この血液流量率の値は, 文献値と大差ないため, 妥当な結果と考えられる. そのため, 本解析モデルは, 今後, 効果的なアンテナ構造や治療方法を検討していく上で有効であると考えられる.

This paper presented evaluation of electromagnetic (EM) energy absorption rate in terms of a specific absorption rate (SAR) in a fetus that was exposed to the EM wave from a portable radio terminal when used in the vicinity of the maternal abdomen. As for the numerical calculation, the electric fields around the antenna were analyzed by the finite-difference time-domain method. We considered analyzing six different positions of the antenna that are located around the waist. The SARs are normalized by 5-W radiated power from the antenna, which were a prevalent input power of wireless radio terminals in Japan. We confirmed that the SARs in the fetus are significantly affected by the distance and penetration path from the antenna to the surface on the fetus. Nonetheless, the SARs in the fetus are lower than the RF safety guidelines for occupational exposure in this paper. © 2010 IEEE.

心臓ペースメーカが動作プログラムの更新を行う際に,従来用いられてきた電磁結合方式に代わる通信方法として,体内植込み型アンテナを用いて外部機器との間で通信を行うシステムが提案されている.そこで筆者らは,体内植込み型医療用データ伝送システムに割り振られている402〜405MHz帯を利用した心臓ペースメーカ装荷型アンテナを検討してきた.本論文では,人体の組織構造が心臓ペースメーカ装荷型アンテナ諸特性に及ぼす影響を評価するため,多層媒質直方体モデルを用いてアンテナ諸特性の数値解析を行った.更に,心臓ペースメーカ装荷型アンテナを高精細数値人体モデル内部に設置し,数値解析により本アンテナの有効性並びに多層媒質直方体モデルの妥当性を検証した.その結果,多層媒質直方体モデルを用いて設計したアンテナは,人体モデルに植え込んでもペースメーカ装荷型アンテナとして有効であることを確認した.

現在,我が国においては,静磁場強度が3TまでのMRI(Magnetic Resonance Imaging)システムが臨床で使用されている.そして更なる画像の高画質化や撮像時間の短縮を実現するために,3T以上の高磁場によるMR撮像技術が研究されている.しかしながら,高磁場化が進むことによるパルス状電磁波の高周波化や,パルスそのものの高出力化により,NMR(Nuclear Magnetic Resonance)信号を送受信するRF(Radio Frequency)コイルに装荷されているコンデンサ容量のばらつきや,その耐圧に問題が生じることが考えられる.そこで,本研究では,集中定数素子であるコンデンサを使用しなくても従来のRFコイルと同等の特性が得られるバードケージコイルを提案し,その諸特性について検討した.その結果,提案したコイルは,静磁場強度が3TのMRIシステムで使用可能であることが示唆された.

This paper attempts to analyze theoretically the propagation characteristics in the transverse section of upper body to support on-body wireless communications. The analytical estimation assumes that the human body is structured as a lossy-dielectric circular cylinder with infinite length that consists of the 2/3-muscle equivalent uniform tissue. Each scattering electric field formulation inside and outside of the cylinder is derived for scattering characteristics in the propagation environment including the human body when the source current has the vertical direction to the cylinder surface or the horizontal direction to the cylinder axis. In order to confirm the reliability of the formulation, total electric field distributions at 2.45GHz are compared with the results by the finite-difference time-domain (FDTD) method. In each current direction, general scattering characteristics and the influence on the total propagation are estimated. Furthermore, from scattering and total electric field intensities evaluated with the variations of operating frequency, radius of the human body, and distance between a source and the human body, propagation characteristics are investigated to assist in the design of a device for on-body propagation channel with the upper body.

人体近傍で用いられる機器のアンテナの設計では,人体との相互作用を考慮することが重要であり,その影響を評価する際には,人体の組織構造を簡易化した均質ファントムを用いた検討が一般的である.しかしながら,均質なモデルを用いることの妥当性の検討例は少ない.本論文では,2〜10GHzにおける人体の組織構造がアンテナ特性に与える影響の基礎的な検討として,均質媒質モデルと人体の組織構造を考慮した層構造モデルの近傍に半波長ダイポールアンテナを配置し,それらの人体構造の差異がアンテナ特性に与える影響について定量的に評価した.また,実験により数値計算の妥当性を確認するために,広帯域層構造ファントムの開発を行った.その結果,アンテナをファントムから0.3λ以上に配置した際の両モデル間の入力特性,放射指向性,放射効率の差異は小さいことを確認した.しかしながら,アンテナとファントム間の距離が0.1λの場合の両モデル間の差異は,VSWRは0.1以上,放射効率は15%以上あるなど,アンテナ特性の差異が大きいことを確認した.

近年,RFID(Radio Frequency IDentification)システムは,個人認証や物流管理などに利用されるなど,普及が進んでいる.読取り対象となるRFIDタグには様々な形状のものが存在し,用途に適したものが選択される.その一例として,リストバンド型のタグを用いた個人認証が挙げられる.しかしながら,リストバンド型のように人体に装着してRFIDタグを用いる場合には,人体の誘電性によりアンテナ特性が変化する.そこで本論文では,リストバンド型RFID用アンテナの特性解析を数値解析及び生体等価ファントムを用いた実験によって行い,人体がアンテナ諸特性に与える影響を評価した.更に,アンテナに反射素子を装荷することによる利得改善の検討を行った.以上の結果より,人体がアンテナ諸特性に影響を与えることを確認し,また,反射素子の装荷により放射特性の改善が可能であることを示した.