Browsing by Author "Xiang, Daopu"

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    Fast Mesh-based physical optics for large-scale electromagnetic analysis
    (Stellenbosch : Stellenbosch University, 2016-12) Xiang, Daopu; Botha, Matthys M.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: At sufficiently high frequencies, the electrical size of scattering objects become very large. The electromagnetic field simulation of such objects becomes prohibitively expensive with physically rigorous (full wave) computational electromagnetics methods. In such cases, methods based on asymptotic assumptions can be employed instead, to approximately solve Maxwell’s equations. The physical optics (PO) approximation for a conducting surface, is a well-known asymptotic assumption. The multiple-reflection PO (MRPO) method is obtained by applying the PO approximation recursively, to model multiple reflections occurring internally to an object. The overall research goal of this work is to significantly accelerate the mesh-based MRPO for electromagnetic scattering analysis. A standard representation was chosen for the surface current, namely Rao- Wilton-Glisson (RWG) basis functions on a mesh of triangle elements. Since the MRPO is an extension of the single-reflection PO (SRPO), the main bottleneck in the SRPO, namely incident field shadowing determination, is addressed first. An adaptive, multilevel, buffer-based shadowing determination algorithm is developed which is robustly optimal, yielding O(N) time-scaling results for extreme test cases (N denotes the number of mesh elements). Secondly, the first ever, comprehensively accelerated version of the meshbased MRPO method (which rigorously takes internal shadowing into account), denoted fast MRPO (FMRPO), is developed. The FMRPO uses the multi-level, fast multipole method (MLFMM) to accelerate internal reflected field calculations. The inter-group interaction criterion of the MLFMM is altered to account for shadowing. Inter-group shadowing status flags are efficiently evaluated. The runtime scaling of the conventional MRPO is O(Nˆ2), while the runtime of the FMRPO scales as quasi-O(N log N), depending on the specific geometry. Results are presented for practical geometries with larger electrical sizes than have ever before been considered with the MRPO, but which can now for the first time be solved in realistically fast runtimes. With the FMRPO there is no fundamental limit to the electrical size of the scattering objects that can be solved.