吉村 博幸

The microwave coagulation therapy(MCT)is one of the minimally invasive microwave thermal therapies and has been employed for the treatment of small size tumor. This paper describes the improvement of the antenna for the MCT.

Recently, the demand for mobile-satellite broadcasting(MSB)is growing. Therefore, we propose in this paper, a simple beam-switching printed array antenna which can fulfil its numerous and demanding requirements. We discuss here the simulations and obtained results.

An experimental evaluation for the SAR(specific absorption rate)is necessary to estimate the interaction between the human body and electromagnetic waves. This paper describes more precise measurement of the SAR distribution in the human head model using the thermographic method.

小形アンテナを検討するうえで, 1Ω以下の微小放射抵抗測定がしばしば必要となる.ところが, ネットワークアナライザを用いた測定においては, 反射係数の絶対値が1に近づくに従って測定精度は悪化する.本報告では, スタブチューナを用いてアンテナと伝送線路間の整合をとって反射を小さくすることにより, Wheeler cap法を用いた微小放射抵抗測定における測定精度の向上について検討を行う.

The efficiency-bandwidth product (EB) is used in the evaluation of small dielectric loaded monopole antennas (DLMAs). The EBs of the DLMAs have been precisely measured on the basis of the Wheeler cap method. As a result, an improvement in the EB of electrically small cylindrical DLMAs has been confirmed experimentally in comparison with that in a bare monopole antenna. In addition, within the category of electrically small antennas considered here, it seems that there exists an optimum value of permittivity for the dielectric loading for which the best EB value is obtained.

In this paper, the microwave interstitial antenna with the dielectric load in part near the tip is introduced to realize the tip-heating and to improve the dependence of the heating patterns on the insertion depth. Numerical simulations using the Finite Difference Time Domain (FDTD) method have been conducted at the frequency of 915 MHz for four different configurations of the coaxial-slot antenna inserted into a catheter: the media between the antenna and the catheter are (a) no, (b) a thin air layer, (c) a thin dielectric layer, and (d) a thin air layer and a dielectric load in part near the tip. The diameter of the antenna including the catheter is sufficiently small for minimally invasive therapy. Comparison of the SARs for the four configurations makes it clear that the dielectric-loaded antenna can realize the best tip-heating and suppress the hot spot near the surface of the human body. Dependence of the SAR distributions on the insertion depth of the antenna has also been examined. It is found from the investigation that the dielectric-loaded antenna has little dependence on the insertion depth.

In microwave hyperthermia for cancer therapy, two power feeding techniques can be utilized: incoherent and coherent operations. In the incoherent operation, not-synchronized microwave pou er is fed into each array element, whereas the coherent operation is achieved by feeding synchronized microwave to the array elements. The authors have been studying the coaxial-slot antenna for interstitial microwave hyperthermia. The antenna is usually employed as an array applicator inserting several antennas into the tissue to generate large heating area. So far we have examined the control of the heating pattern by feeding techniques in order to obtain more uniform and enlarged heating region. Particularly, 'tip-heating,' which means sufficient heating at the area near the tip of the applicator, is significant riot to damage surrounding normal tissue in interstitial hyperthermia. In this paper, two feeding techniques are combined and calculated temperature distributions in a hexagonal array applicator are examined by solving Pennes bioheat transfer equation by finite difference method. As a result, in the coherent feeding;, large heating area was obtained, while better tip-heating was achieved in the incoherent feeding. Moreover. an instance of sequential combination of two feeding techniques is depicted. Tn this case, temperature distribution had both characteristics of large heating area and tip-heating, therefore the ability of the control of heating characteristics by sequential combination of the coherent and the incoherent feedings was presented.

A fractional cross-spectral density is defined by use of an optical fractional Fourier transform based on the rotation of a Wigner distribution function within the accuracy of the paraxial approximation. The properties of the planar Gaussian Schell-model (GSM) source field in a fractional Fourier plane are analyzed theoretically. As a result, it becomes clear that the extent, the wave-front-curvature radius, and the spectral shift of the fractional Fourier field depend strongly on the fractional order of the Fourier transform, the Fresnel number associated with the GSM source size, and the scaled spatial-coherence length of the GSM source. © 1997 Optical Society of America.

The ambiguity function properties of a Gaussian Schell-model (GSM) beam are theoretically analyzed in the paraxial approximation. In analysis the behavior of an equi-ambiguity-function ellipse (trajectory of the ambiguity function at a constant value) is investigated in connection with the propagation properties of the GSM beam. As a result, its behavior is revealed in relation to the fundamental beam parameter, by which both the GSM beam radius and the wave-front-curvature radius of the beam are uniquely described as a function of the propagation distance. In addition, the effects of both the propagation distance and the spatial coherence of the GSM source on the behavior of the ellipse are investigated. © 1994 Optical Society of America.

The mutual intensity of the optical field in the Fraunhofer diffraction region from the end of an optical fiber is analyzed theoretically by using a fiber-end source model. Tn this source model, the optical field at the end of the fiber is expressed as a sum of independent plane waves with random directions and phases since the guided modes propagating through an optical fiber may be regarded as a stochastic process. It is found that the spatial coherence property of the optical field in the diffraction region is not homogeneous but quasihomogeneous in a statistical sense. This property is discussed in connection with the V number of the fiber and in comparison with that of the optical field, obeying the van Cittert-Zernike theorem, produced by the incoherent source. © 1988, SPIE.