Investigation Of FEM And BIM On Electromagnetic Scattering From Rough Surface And Target

Both finite element method(FEM) and boundary integral method(BIM) are applied in this dissertation to study the properties of the electromagnetic(EM) scattering from a rough surface and the composite scattering from a rough surface with a target above/below it. To improve the simulational efficiency of BIM, the Kirchhoff approximation(KA) is applied to combine with BIM. Based on the perfectly matched layer, FEM is introduced into the study of composite scattering from the one-dimensional(1-D) rough surface and a two dimensional(2-D) target. To study the scattering problem about the rough surface and the target, the hybrid FEM/BIM is developed, and KA is used to improve the efficiency of FEM/BIM. Finally, a hybrid method combining FEM and method of moments(Mo M) is applied to discuss the scattering from a three dimensional(3-D) target and the 2-D rough surface. Main works of this dissertation are as following:1. For the composite scattering from 2-D a target buried beneath the 1-D dielectric rough surface, KA is used to simulate the scattering field of the rough surface, and the target is studied by BIM. The coupling between two regions can be considered by an iterative algorithm. This hybrid method can improve the simulational efficiency of the composite problem.2. The FEM/PML is introduced to study the composite problem of the rough surface and the target. To truncate the half-open region, PML is applied, and the interior domain is handled with FEM. Based on this method, the composite problem of 1-D rough surface with a target above/below it and 1-D multilayer rough surfaces with a 2-D target buried in it are discussed.3. To reduce the computational domain of the problem about rough surfaces, BIM is used as the truncated boundary of the FEM region, and the theories and the equ ations of FEM/BIM are given in detail for the scattering problem of the rough surface and the target.4. To improve the simulational efficiency of FEM/BIM, KA is introduced to combining with it, which obtains a hybrid high-low frequency method. The composite problem is divided into two domains. The domain of rough surface is treated with KA, and the domain of target is studied by the FEM/BIM. An iterative algorithm is used to consider the coupling effect between two domains. To improve the precision of the hybrid method, the rough surface is divided into multiple subdomains based on the multireigon algorithm. The dominant region of the rough surface is simulated by BIM, while the other subdomains are studied by KA.5. Based on the vector tetrahedral basis function, the 3-D target is calculated by FEM/Mo M. Combining with RWG basis function, Mo M is applied to study the scattering from the 2-D rough surface. The coupling effect between the target and the rough surface is considered by integral boundary, and then the hybrid method is applied to study the composite scattering problem of the 2-D rough surface and the 3-D target.