伊藤 公一

ワイヤレスカードシステムは, 電波を利用することにより, カードをデータ読み書き装置に接触させることなく, 情報のやり取りを行うことを目的とする。ワイヤレスカードの技術は, 料金徴収, ID管理, 履歴管理および位置管理等の広範な利用分野において様々な応用が可能であり, 社会生活の利便性を向上させ, 高度情報通信社会推進の一翼を担う技術として大きく期待されている。本稿では応用例として, 有料道路の自動料金収受システム, 鉄道の自動改札システム, FA生産ラインシステムおよび特定区域への入退場管理システムに関する現状を紹介すると共に将来を展望する。

近年, 携帯無線機への小形化要求はますます強まっており, なかでもページャではその傾向が著しく, 腕時計に内蔵されたタイプの製品も実用化されている.本論文では腕時計のバンド部分に内蔵するアンテナとして提案されている小形スロットアンテナについて, 本アンテナが人体に密着する形で使用されることから, 実使用時のアンテナ特性に関しては, 人体をアンテナ構造体の一部として考える必要があり, このため計算用および実験用の人体モデルを作成し, 人体に小形スロットアンテナを装着した場合の放射特性について測定・計算を行った.その結果, 人体装着時においても約-15dBdと, ページャ用アンテナに要求される-30dBd程度の利得に対し, 十分な特性が得られることを示した.また, 人体装着時に腕時計使用者の姿勢による放射特性の変動についても検討を行い, 腕が振られた場合, 使用者が腕時計を見ている場合等について実際に測定・計算を行った.この結果, 使用者の姿勢変化に対してもページャ用アンテナとして十分な特性が得られることを示した.

従来より, SAR (Specific Absorption Rate) による加温機器の性能評価がひろく行われているが, 温度の値そのものによる評価ができればより望ましい.そこで本研究においては, ハイパーサーミア機器の加温特性に関する以下の定量的な評価指標を導入した.それらは, 最大加温長Hm₄₃, 最大加温径D_m43, 最大加温体積V₄₃, 深部有効加温体積比R_V43および最高温度T_maxである.一例として, 治療温度を43℃以上とした場合において, 同軸スロットアンテナで構成した組織内加温用アレーアプリケータの特性を数値解析により求め, 血流量, 入力電力と評価指標の関係を整理したチャートを作成した.それらのチャートより, アプリケータ加温特性の全体把握および定量的比較が可能であることがわかる.また, 腫瘍の位置や体積などに応じ, 本論文で示したようなチャートより適切な入力電力を決定できる.以上の指標による評価は, アプリケータの設計のみならず治療計画支援の場においても有用である.今後は, teq43等の治療時の測温データより得られる指標との併用を検討していく必要がある.

人体と電磁界の影響を検討するための生体モデルとして, さまざまなファントム(模擬生体)が提案されている.本論文では, 筆者らが開発した生体と等価な電気的特性を実現したファントムの特性について報告し, その通信及び医療応用の例を示した.本ファントムは寒天, ポリエチレン粉末, 塩化ナトリウム, TX-151, 保存料及びイオン交換水からなる, 高含水組織の比誘電率及び導電率を模擬したファントムである.本ファントムは300MHz〜2.5GHzの周波数帯域にわたり, 単一の組成比で生体組織とほぼ等しい電気的特性を実現している.また, 組成の調整により任意の高含水組織の電気的特性を模擬することが可能である.製作に特殊な設備を必要とせず, 保存性も良好である.更に, その人体モデルへの応用例として, COST244人体頭部モデル及びハイパサーミア用同軸スロットアンテナにおけるSAR計測の例を示した.本ファントムは人体と電磁界の相互的な影響を考慮するための人体モデルとして有用である.

最近, 給電線路にコプレーナ線路を用いたプリントアンテナが盛んに研究されている. コプレーナ線路は, 中心導体と接地板とが同一千面上にあるので, アクティブ素子の接続が容易であるため, アクティブアンテナの給電線路に適している. 従来, コプレーナ給電のアンテナとしては, パッチアンテナ, ループアンテナ, スロットアンテナ等の直線偏波のアンテナについては報告されているが, 円偏波アンテナに関するものは少ない. そこで本論文では, スロットループで構成したコプレーナ給電円偏波アンテナの動作原理をFDTD法を用いた電磁界シミュレーションの結果から明らかにした.

本論文では,腕時計型ページャのバンド部分に内蔵する小形スロットアンテナを提案する.円筒および平板形状のアンテナの放射特性に着目して,実験および理論計算を行い,ピーク利得-14dBd以上の良好な特性を得た.また,アンテナの大きさに関する依存性も検討した.

The interstitial hyperthermia is an invasive heating method applied by inserting the applicator into the human body. We have been studying on coaxial-slot antennas for interstitial microwave hyperthermia. The characteristics of the square antenna array were theoretically examined. Firstly, the basic structure of the antenna, and a simplified analysis model taking account of the effect of the boundary surface were explained. Then analysis was performed by using the moment method. Finally, the calculated results were discussed. The catheter thickness has much effect on the characteristics and must be considered both in designing and in using the antenna. When the array spacing was increased, the effective heating area became larger and more uniform. As the insertion depth was increased, the effective heating area was also enlarged.

This paper describes that the dielectric characteristics of a catheter around the interstitial antenna have an effect on the wavelength for current, and this effect results in the variation of the SAR (Specific Absorption Rate) distribution around the antenna. A theoretical study of SAR distribution around a coaxial-slot antenna is performed. Analytical technique used is the moment method. Result and discussion on the effect of material and thickness of the catheter are presented. The wavelength for the current shortens with increasing dielectric constant or decreasing thickness of the catheter. Due to this variation of the wavelength for current, the SAR distributions take various shapes.

This paper describes an analysis of the coaxial-slot antenna, which is an effective antenna for interstitial microwave hyperthermia. The structure of a coaxial-slot antenna for analysis is described. The antenna is modeled as a vertical antenna penetrating the interface between the air and a lossy medium. In this analysis, the full-wave spatial Green's function is approximated by an exponential polynomial, and a catheter around the antenna is replaced with an equivalent polarization current. An electric current distribution along the antenna is calculated by using the moment method and an electric field distribution around the antenna is derived from the current distribution. We present the results of our calculations and discuss the effect of the antenna insertion depth on both the current and electric field distributions.

The validity of numerical design scheme of CP-PASS (Circularly Polarized Printed Array antenna composed of Strips and Slots) is considered. The strip element of CP-PASS is composed of a strip dipole and a window which increases the frequency bandwidth of the strip element. With the window, however, analysis of the antenna becomes difficult if a simple analytical model is used. The previous design procedure requierd an experimental procedure. By using modern computers, the FDTD (finite-difference time-domain) method becomes powerful tool for the analysis of 3D-structured antennas. In this paper, numerical results of the FDTD analysis for CP-PASS is compared with results from experiments. The characteristics of the unit-radiator of CP-PASS are demonstrated numerically This paper shows that CP-PASS can be designed numerically and a new path has opened in the study of CP-PASS.

A radial line slot antenna radiating a circularly polarised conical beam is proposed. It is advantageous in the construction of a feeding structure comparing with conventional antennas. Guidelines For the design of the slot arrangement are presented. The experimental results, which are in good agreement with the design, demonstrate the conical beam radiation.

The Wheeler cap method is an easy and accurate way to measure the radiation efficiency of small antennas, and has been analysed by other investigators using a wire-grid model. However, it is more reasonable to use a surface-patch model for the cap instead of the wire-grid model. This would avoid the inevitable leakage from the wire grid. The authors confirm the validity of the simulation using the surface patch for the Wheeler cap with NEC2 (numerical electromagnetics code 2 developed by Lawrence Livermore National Laboratory).

A practical design procedure for a circularly polarized printed array antenna composed of strip dipoles and slots (CP-PASS) is presented. CP-PASS is a kind of series-fed array, and the equivalent circuit model of CP-PASS is simplified to be suitable for a computer-aided design (CAD) package. Some experimental results of a new strip element excited by a stripline and a 9-element set CP-PASS are also presented. (C) 1994 John Wiley & Sons, Inc.

CP-PASSは, 素子および給電系の構造が単純, 能動素子との組合せが容易, などの特長を有する本報告では, このアンテナの構成素子である「窓付ストリップダイポール」についてFD-TD法を用いて理論解析を行った

CP-PASSは, 素子および給電系の構造が単純, 能動素子との組合せが容易, などの特長を有する本報告では, このアンテナの構成素子である「窓付ストリップダイポール」についてFD-TD法を用いて理論解析を行った

Conical beam pattern is well suited for low mobile or maritime mobile antennas used in cheap and low G/T satellite communication system. Various solutions have been already proposed to generate circular polarized conical patterns; some authors use single microstrip patch working on higher order modes [1], [2], while others have built arrays of patches [3] -[5]. The present letter describes the design of an array of slot fed patches with its feed network and the experimental results which have been obtained in S-band.

We have developed a microwave coaxial ring-slot applicator for interstitial hyperthermia and have tested it on muscle-equivalent agar phantoms. Based on these results, the clinical use of this applicator was evaluated in animal experiments and in combination with operation of a clinically used microwave hyperthermia system.<BR>The applicator delivers 400-430 MHz microwaves produced by a signal generator (Type 8656A Hewlett Packard Co.) and a power amplifier (RF Power Labs Inc.), and is made of a 0.86 mm coaxial semirigid cable. Several ring slots, which radiate microwave power into the surrounding tissue, are placed at equidistant intervals along this semirigid cable on the outer conductors, and the tip of the coaxial cable is short-circuited to expand the terminal heating region. This antenna can be inserted into a 21 G plastic catheter and the specific absorption rate (SAR) distribution along it can be changed by adjusting the parameters of the slots. The applicator inside a catheter was inserted into normal rabbit muscles and into VX-2 tumors implanted in the thighs of rabbits. Temperature distributions were measured by fluoroptic thermometers (Luxtron model 3000) or thermocouples. The locations of the antennas and thermal probes were identified by CT scanning after heating, and the thermal distribution was obtained by a combination of computer simulation and the raw thermometry data.<BR>When a single antenna (6 cm active length) was inserted into the muscle and supplied with a power of 20 watts for 6 minutes, it heated the tissue in a radius of 13 mm along the applicator to >42°C. Two antennas (4 cm active length) were inserted 2 cm apart into a 5.5x 4x 3 cm tumor, and four were inserted into a 7x 6x 2cm tumor at 0.5-cm intervals. Almost all regions of each tumor were heated to > 41°C. Histological examination of the tumors 3 days after heating showed necrosis, nuclear pyknosis and endthelial destruction with hemorrhage in the areas heated to > 43°C on the computerized temperature simulation made using thermometry data. Moreover, 5 applicators (4cm active length, 4 on the corners of a square with 4 cm sides and 1 at the center) were horizontally inserted into a tumor with a diameter of 5 cm, and operated at a power of 60 watts for 5 minutes, followed by 55 watts for 5 minutes and 50 watts for 8 minutes. Almost all parts of the tumor were heated to >41°C. Finally, 4 applicators (4cm active length) were longitudinally inserted into a tumor with a diameter of 8 cm at 3-cm intervals, and supplied with a power of 30 watts for 8 minutes and then 20 watts for 2 minutes. Almost all parts of the tumor were heated to >43°C.<BR>These animal experiments demonstrated several advantages of this newly-developed microwave applicator, including a relatively large heating area when multiple applicators were used, relatively uniform heating along the applicator, and the small diameter of the applicator. Moreover, this applicator could operate using microwaves generated by a 430 MHz microwave hyperthermia system with an electric field converging (lens) applicator, which is already clinically used for heating localized subsurface tumors in some institutions.<BR>The feasibility of this applicator for clinical use appears worth investigating further. It is seems possible that interstitial hyperthermia using the ring-slot array applicator may eventually be performed in combination with intraoperative radiotherapy by implanting angiocatheters into tumors at operation, or else it could be applied after an angiocatheter was inserted under CT guidance.