Shadow Boundary Currents in the Problem of High-Frequency Electromagnetic Diffraction by a Circular Impedance Cylinder

概要

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A correction of the physical optics approximation by accounting for the presence of specific currents concentrated near shadow boundaries on the surface of a convex nonmetallic scatterer is analysed by considering a canonical problem of diffraction of a plane electromagnetic wave incident normally to the axis of an infinite circular cylinder with impedance boundary conditions. The analysis focuses on the development of Fock-type asymptotic representations for magnetic fields tangent components on the surface of scatter. The Fock-type representation of the surface field is uniformly valid within the penumbra region, providing a continuous transition from the geometrical optics formulas on the lit portion of the surface to the creeping waves approximation in the deep shadow region. A new numerical procedure for evaluating Fock-type integrals is proposed that extracts rapidly varying factors and approximates the rest, slowly varying coefficients via interpolation. This allows us to obatain accurate and simple representations for the shadow boundary currents that can be directly inserted into the radiation integral and effectively integrated. We show that accounting for the shadow boundary currents considerably improves the traditional PO analysis of the high-frequency electromagnetic fields scattered from smooth and convex non-metallic obstacles, particulary near the forward scattering direction.
社団法人電子情報通信学会の論文
1998-10-25