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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/35661

    Title: 應用最佳化法則於時域重建二維均勻介質柱體之特性研究
    Other Titles: Characteristic studies of time domain inverse scattering for 2-D homogeneous dielectric cylinder by applying optimization method
    Authors: 黃中信;Huang, Chung-hsin
    Contributors: 淡江大學電機工程學系博士班
    李慶烈;Li, Ching-lieh
    Keywords: 基因法則;粒子群聚法;差異形演化法;逆散射;有限時域差分法;Genetic Algorithms;particle swarm optimization;Differential Evolution;Time Domain Inverse Scattering;Finite Difference Time Domain
    Date: 2009
    Issue Date: 2010-01-11 06:58:33 (UTC+8)
    Abstract: 本論文研究埋藏於自由空間、半空間與三層空間中二維均勻介質柱體的電磁影像重建。此研究以有限時域差分法 (FDTD) 為基礎,利用最佳化方法於時域中重建埋藏於不同空間中二維均勻介質柱體之特性參數。其中,對於描述形狀的方法,於正散射我們使用傅立葉函數展開(Fourier series expansion) ,並於逆散射中使用三次仿樣函數展開(cubic spline),另外,為了使柱體的形狀更為圓滑我們使用了次網格技術。
    This dissertation presents the studies of microwave image reconstructions that are approached based on the time-domain technique (finite difference time domain, FDTD) and several optimization methods for a 2-D homogeneous dielectric cylinder. The dielectric cylinder is located in free space, or buried in half-space media, or embedded in a three-layered material medium, respectively. For the forward scattering the FDTD method is employed to calculate the scattered E fields, while for the inverse scattering several optimization methods are utilized to determine the shape, location and the permittivity of the cylindrical scatterer with arbitrary cross section. The subgirdding technique is implemented for the FDTD code in order to model the shape of the cylinder more smoothly. In order to describe an unknown cylinder with arbitrary cross section more effectively during the course of searching, the closed cubic-spline expansion is adopted to represent the scatterer contour instead of the frequently used trigonometric series. The former is still used in the forward scattering part.
    In order to explore the unknown dielectric cylinder in different environments, an electromagnetic pulse can be conducted to illuminate the cylinder, for which the scattered E fields can then be measured. The inverse problem is then resolved by an optimization approach. The idea is to perform the image reconstruction by utilization of some optimization scheme to minimize the discrepancy between the measured and calculated scattered field data. Three optimization schemes are tested and employed to search the parameter space to determine the shape, location and permittivity of the dielectric cylinder. They are the modified particle swarm optimization (MPSO), the dynamic differential evolution (DDE) and the non-uniform steady state genetic algorithm (NU-SSGA).

    The suitability and efficiency of applying the above methods for microwave imaging of a 2D dielectric cylinder are examined in this dissertation. Numerical results show that even when the initial guesses are far away from the exact one, good reconstruction can be obtained by all these optimization methods. However, the DDE and MPSO outperform the NU-SSGA regarding the reconstruction accuracy and the convergent speed in terms of the number of the objective function calls.
    Appears in Collections:[電機工程學系暨研究所] 學位論文

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