Abstract-An accurate and efficient computational approach is presented for analyzing radiation characteristics of large antenna arrays with radome. This approach is based on the hybrid finite elementboundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA). Unlike the conventional singledomain FE-BI-MLFMA, the whole domain of the antenna array with radome is separated into many disconnected domains. A large free space area unavoidable in the single-domain FE-BI-MLFMA is eliminated in this multi-domain FE-BI-MLFMA formulation, thus the number of unknowns is greatly reduced in the presented multi-domain FE-BI-MLFMA approach. Different from the single-domain FE-BI-MLFMA, many integral equations are required in this multi-domain FE-BI-MLFMA. The numerical experiment shows that the presented multi-domain FE-BI-MLFMA is more efficient than the singledomain one while maintaining the same accuracy. A whole complicated system of a slotted-waveguide array with radome mounted on an aircraft is analyzed to further demonstrate the generality and capability of the presented multi-domain FE-BI-MLFMA.
An analytical method for electromagnetic scattering characteristics of complex unmanned aerial vehicle targets by using hybrid multilevel fast multipole algorithm (MLFMA)-physical optics (PO) and short-time fourier transformation (STFT) is proposed in this paper. By constructing accurate electromagnetic models of unmanned aerial vehicle (UAV) target with inlet, the aspect and polarization characteristics of radar cross section (RCS) and time-frequency representation (TFR) are studied. To validate the influence of the inlet, the monostatic and bistatic RCS at specific angles, RCS statistical characteristics and TFR correlation are simulated and compared. It is concluded that the inlet should be sufficiently considered to calculate the accurate scattering characteristics.
Abstract-It has been widely verified that the hybrid finite element -boundary integral -multilevel fast multipole algorithm (FE-BI-MLFMA) is a general, efficient and accurate method for the analysis of unbounded electromagnetic problems. A variety of fast methods of FE-BI-MLFMA have been developed since 1998. In particular, the domain decomposition methods have been applied to FE-BI-MLFMA and significantly improve the efficiency of FE-BI-MLFMA in recent years. A series of fast domain decomposition methods (DDMs) of FE-BI-MLFMA have been developed. These fast DDMs can be roughly classified into two types: Schwarz DDMs and dual-primal finite element tearing and interconnecting (FETI-DP) DDMs. This paper will first give an overview of the DDMs development of FE-BI-MLFMA. Then a uniform, consistent, and efficient formulation is presented and discussed for these fast DDMs of FE-BI-MLFMA. Their computational complexities are analyzed and studied numerically.
Traditional electric discharge machining (EDM) uses the copper electrode to machine polycrystalline diamond (PCD), and the machining efficiency and machining quality have been poor. To improve the machining efficiency and machining quality, this study uses white copper as the electrode to machine the surface of the PCD workpiece and adds graphene powder to the dielectric for mixed powder EDM. The surface properties and processing mechanism of PCD under different processing methods were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy, and the surface quality and processing efficiency of PCD were analyzed by material removal rate (MRR) and surface roughness (SR). The results showed that the MRR of the white copper electrode increased by 65% compared with that of the purple copper electrode at low parameters, and the MRR increased again by 87% after adding graphene, and the SR decreased by 13%. The graphitization of PCD diamond processed by the white copper electrode was greater than that of the purple copper electrode by Raman spectroscopy and XRD analysis, and the addition of graphene increased the graphitization again. The results show that when processing with copper electrode, the way of processing PCD is mainly to remove the binder, and the effect of processing diamond particles is not obvious; when processing with white copper electrode, making diamond graphitization is the main removal method, and after adding graphene in the dielectric, the removal method changes to a combination of diamond graphitization and high discharge energy removal.
This paper incorporates the compensated Mitzner boundary conditions (CMBC) into the hybrid finite elementboundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) for fast and accurate computation of scattering by three-dimensional inhomogeneous objects with thin dielectric structures. In this CMBC-FE-BI-MLFMA, each thin dielectric layer is reduced to an interface with zero thickness; then CMBC is applied to establish the relation of electromagnetic fields across the interfaces. This approach can reduce the amount of computation and remain the advantages of versatility, accuracy, and efficiency of the conventional FE-BI-MLFMA algorithm. The formulation of this CMBC-FE-BI-MLFMA is presented in this paper. An efficient preconditioner based on the sparse approximate inverse is employed and further parallelized on memory-distributed platforms. Numerical results are presented to demonstrate the accuracy, efficiency, and capability of the parallel CMBC-FE-BI-MLFMA.
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