Iterative Physical Optics And Its Fast Algorithm

A modern aircraft operates in a rigorous external electromagnetic environment, includinghigh-intensity radiated fields (HIRF) and lightning etc. These external radiated fields can penetrateinto the cabin through apertures, cracks, windows and composite skins on the fuselage, and thencouple into airborne electric/electronic equipment through its connected cables and apertures onenclosure. That may interfere with the normal operation of equipment, even threat the flight safety ofairplane. So, it is very important and valuable to investigate the efficient methods for simulating theelectromagnetic field and related coupling issues in a complex cabin.The fast methods for calculating the electromagnetic environment in the cabin are studied asfollows:1. Using the RWG (Rao-Wilton-Glisson) basis expansion, the iterative physical optics (IPO) andits program implementation are studied deeply. This is the foundation for the latter presented fastalgorithms of IPO. To deal with the slow convergence even divergence of original IPO, the Jacobiminimal residual (JMRES) algorithm is employed to accelerate its iterative process. Thereafter,combined with the domain decomposition method (DDM), an efficient algorithm for calculate theelectromagnetic behavior of complicated cavities with inner shadow regions is presented. Theaccuracy of the presented algorithms is demonstrated by several numerical results.2. The equivalent dipole-moment (EDM), fast dipole method (FDM) and multilevel fast dipolemethod (MLFDM) are introduced to accelerate the computation of IPO integral. By using the conceptof EDM, a closed-form solution of the IPO integral is derived. Thereafter, to accelerate the calculationof IPO integral, the interaction of each two bases in two nonadjacent groups is transformed into theform of aggregation-translation-disaggregation, by adopting the Taylor’s series expansion andgrouping scheme in FDM. Numerical results of several cavity scattering cases show that theefficiency of calculating IPO integral is improved greatly by the presented fast algorithms, and furtherimproved by MLFDM.3、The applicability of the presented fast IPO methods in calculating the electromagnetic fielddistribution in the open cabin is researched. To efficiently simulate the electromagnetic couplingbehaviors of cables in the cabin, the former fast IPO methods are combined with BLT(Baum-Liu-Tesche) equation. The effectiveness of presented method is demonstrated by twofield-cable coupling cases in a rectangular cavity and in a cylindrical cavity, respectively.