Cấu trúc sóng chức năng trong điện lý thuyết P7

SAR Distributions in a Head ModelThe development of cellular telephones and mobile communication systems has led to a growing awareness of the vital role that wireless systems play in communication networks and the biological effects of EM fields on users. Since cellular hand phones are operated in close proximity to human heads while in use, there has been increasing public concern about the health effects of the human head exposed to EM energy emitted from mobile handset antennas.
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Cấu trúc sóng chức năng trong điện lý thuyết P7 Spheroidal Wave Functions in Electromagnetic Theory Le-Wei Li, Xiao-Kang Kang, Mook-Seng Leong Copyright  2002 John Wiley & Sons, Inc. ISBNs: 0-471-03170-4 (Hardback); 0-471-22157-0 (Electronic) 7 SAR Distributions in a Spheroidal Head Model7.1 INTRODUCTIONThe development of cellular telephones and mobile communication systemshas led to a growing awareness of the vital role that wireless systems play incommunication networks and the biological effects of EM fields on users. Sincecellular hand phones are operated in close proximity to human heads while inuse, there has been increasing public concern about the health effects of thehuman head exposed to EM energy emitted from mobile handset antennas.To avoid the harmful effects of EM fields radiated by mobile phones, designersof hand-phone antennas must be able to develop highly efficient, low-profileantennas that can be mounted on handheld transceivers and operated in theproximity of human tissues. To evaluate potential health effects, the specific absorption rate (SAR) isnormally used to evaluate the rates of EM energy deposition in animal orhuman tissues. An important motivation for researchers is to gain a detailedunderstanding of the EM field distribution and power absorption distributioninside the human head [138,139]. There exist a variety of techniques that canbe used to perform the required analysis of SAR deposition in human heads,each with its own strength and weakness. In the analysis, the model obtainedfrom medical imaging serves as a realistic model but requires a lot of compu-tational time as in the methods of finite element [140], finite difference [141- 1451, and moments [146,147]. To increase computational speed, the sphericalhuman head model is also often adopted as an idealized representation of areal biological human head in the analysis [ 14%1511, but it. is less accurate. 191192 SAR DISTRIBUTIONS IN A SPHEROIDAL HEAD MODELIn view of the fact that the geometry of a human head can be better approxi-mated by a prolate spheroid than a simple sphere and that the computationaltime can be saved as compared with those using the finite difference timedomain (FDTD) technique and the finite element method (FEM), a dielectricprolate spheroidal model serves as a compromise for the full-wave analysisof EM field distributions. Investigation of the prolate spheroidal head modelpresented in this chapter can serve as a complement of the existing analysesof analytical models of the human head.7.2 MULTILAYERED PROLATE SPHEROIDAL HEAD MODELIn this analysis the human head is modeled as a multilayered dielectric prolatespheroid, as shown in Fig. 7.1. The multilayered spheroidal model is definedsimilarly to that of multilayered spherical head models in previous analyses[148,151,152]. The dielectric spheroidal model consists of six layers: brain,CSF (cerebrospinal fluid), dura, bone, fat, and skin, respectively. To makereasonable assumptions, the maximum major and minor semiaxial lengths ofthe outer layer (the layer of skin) is assumed to be 10 cm and 7.5 cm, re-spectively. The thickness of each layer along the direction of the minor axisis assumed to be the same as that employed in 11511. The region of eachlayer of the human head is labeled as 1, 2, . . ., 6, and the wave propagationswithin the layer is k1, k2, . . ., and k6, respectively. The outside region of thehead model (where the mobile antenna is located) is labeled as 7, whose wavepropagation constant is k7. To simplify the computation, each spheroidal in-terface is assumedto have the same interfocal distance d. This is a reasonableapproximation when the first inner region of brain is much thicker than thatof other modeled layers of tissues [33,49], as shown in Table 7.1. In this book, two frequencies of mobile antennas are studied: the GSM (Pan European Cellular System-Group Special Mobile, with center frequencyabout 900 MHz) and the PCN (Personal Communications Network, with cen-ter frequency about 1800 MHz). The dielectric constants of each region at theGSM and PCN frequencies, as well as those used in spherical head models orFDTD analyses [139,141,145,148,153,154], are provided in Table 7.1. The antenna is modeled as a A/4 monopole or dipole (as shown in Fig. 7.1)located at a distance s away from the multilayered spheroidal model. Tosimplify the computation, the orientation of the monop ...