| Currently,the problem of computational electromagnetics(CEM)in electromagnetic engineering applications is becoming more and more complex.Most of the targets feature complex materials and geometries,such as multilayer dielectric targets,large multi-scale targets,and composite metallic and dielectric targets.This dissertation focus on improving the capability of computational algorithms of the surface integral equation(SIE)method of moments(Mo M)in solving these complex problems.Efficient solutions of SIE Mo M are studied and explored for the calculation of complex targets.The computation of scattering from multilayer dielectric bodies is studied by using the combined tangential formulation(CTF)of surface integral solution.It is found that the CTF matrix equation system converges slowly,especially for multilayer dielectric bodies which has large matrix dimension and large condition number of impedance matrix.To speed up its iterative solution,the preconditioning schemes are designed.A simple and efficient preconditioner named the Distance Sparse Preconditioner(DSP)is designed in this dissertation for the surface integral solution of multilayer dielectric bodies,and validated by numerical experiments.Compared with the traditional near field preconditioner,the proposed preconditioner significantly reduce CPU time and memory requirement.Furthermore,an efficient preconditioning approach is designed for multilayer dielectric bodies in this dissertation by recursively employing the Schur complement approximation and lower triangular approximation.We call this preconditioning approach as the recursive approximate Schur preconditioner with lower triangular approximation(R-ASP-LT).A series numerical results are presented to show the capability of the preconditioning approach for multilayer bodies,especially for lossless large multilayer radomes.In addition,the trick of efficiently implementing Multilevel Fast Multipole Algorithm(MLFMA)is presented for multilayer dielectric bodies.By combining the calculation of the far-field interactions that have the same aggregation and translation process in each matrix-vector multiple of the iteration,the iteration time of the calculation of the multilayer dielectric target is greatly reduced.The domain decomposition methods(DDM)are studied in solving the large multiscale electromagnetic scattering problems,with special attention to the discontinuous Galerkin(DG)method.Firstly,different schemes of the discontinuous Galerkin method are studied systematically.The unified idea of the DG method establishment which is different from the existing literatures is proposed,and the validity of this idea is verified by numerical examples.The efficiency and flexibility of the DG method compared with the traditional method are verified.Then the efficient implementation scheme of DG based on SIE is proposed for scattering from large multiscale homogeneous objects.More specifically,the formulation of DG for homogeneous bodies is derived from the CTF equations and the approach of DG method is proposed.The differences of DG for penetrable and non-penetrable objects are presented by numerical experiments.The problems such as the parameter setting of the DG method are discussed,and the numerical performance of the proposed method is analyzed and verified.Finally,the DG method base on SIE for the composite metallic and dielectric structures is proposed.The SIE of the composite target is derived and the domain decomposition scheme of the target is designed.A series of composite targets are calculated to prove the validity of the method. |
