The method of moments (MoM) [1] is preferred in the solution of electromagnetic scattering problems, which converts integral equations into a dense linear matrix system. However, it places a considerable burden on the computational complexity and memory requirement when the electrically large target is analyzed. Recently, some iterative solvers, such as the multilevel fast multipole method (MLFMM) [2] based on addition theorem for spherical harmonics, the adaptive integral method (AIM) [3]: a fast iterative integral-equation solver through splitting the impedance matrix into near-field and farfield components, and the adaptive cross approximation (ACA) algorithm [4], which is a low-rank decomposition method, are developed to improve the calculation of the MoM. Unfortunately, these iterative methods suffer from convergence problems of ill-conditional matrices for electrically large targets under analysis. Especially, when the monostatic scattering problems are considered, the iterative process need be repeated for each excitation.
The characteristic basis function method (CBFM) [5, 6] is an iteration-free method, which can speed up the direct solution of the MoM matrix equations by dividing the target into multiple adjacent blocks. For each block, the CBFM constructs macro basis functions called characteristic basis functions (CBFs) which indicate the current distribution of each block. And the number of CBFs is smaller than that of the RWG basis functions proposed by Rao et al. [7] in 1982. In [8], a singular value decomposition based CBFM (SVD-CBFM) is proposed to solve multiple excitation electromagnetic scattering problems. An improved SVD-CBFM [9] is presented to further reduce the number of incident plane waves and CBFs. However, as the electrical size of target increases, the size of each block will become large with retaining a proper number of blocks. This will lead to the increase of unknowns of each block, and the construction of CBFs becomes very time consuming.
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It is well known that the target needs to be first divided into multiple blocks when the CBFM is applied, but the size of the blocks has a great impact on computational time and storage consumption. In order to achieve the minimum calculation time, the numbers of blocks and unknowns N should be satisfied with [Please download the PDF to view the mathematical expression] according to [12]. However, when the electrically large target is analyzed, it is usually divided into large blocks for improving the efficiency of calculation. The larger the size of blocks is, the smaller the reduction matrix which can be easily solved [13] is. Inevitably large subdomain contains more unknowns, and the procedure of generating CBFs will become very time consuming. In order to mitigate this problem, a novel HCBFM is proposed in this paper. In HCBFM, the electrically large target is firstly divided with hierarchical partitioning approach, and at each incident plane wave, the high-level CBFs defined in large block are expressed as a linear combination of the previously generated low-level CBFs defined in the corresponding small block, which can avoid directly solving the CBFs in the large block. Suppose that the target is firstly divided into M blocks, then each block is subdivided into N subdomains, and these subdomains can be further divided until the lowest level subdomains contain a few of RWG basis functions. For instance, as shown in Fig. 1, the target is firstly divided into four (M = 4) blocks called the second-level. Each block is subdivided into nine (N = 9) subdomains, called the first-level. The solid dot denoted as 1 9 in Fig. 1 stands for the ninth subdomain of the first block.
[13.] Laviada, J., F. Las-Heras, M. R. Pino, and R. Mittra, "Solution of electrically large problems with multilevel characteristic basis functions," IEEE Transactions on Antennas and Propagation, Vol. 57, No. 10, 3189-3198, 2009
PHY2054 (Physics 2 without calculus) is the second semester of Physics without calculus, covering electrostatics, electric current, electric circuits and their components, magnetism, induction, electromagnetic waves, optics, optical devices, interference and diffraction. It is typically, but not exclusively, taken by biological sciences majors and pre-professional students, i.e., those planning careers in health care, optometry, pharmacy, etc. It is not a suitable course for physics, chemistry or engineering majors, who are encouraged to take PHY2049 (Physics 2 with calculus) or PHY2061 (enriched Physics 2 with calculus), both of which offer similar material but with more mathematical emphasis. 2ff7e9595c
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