Implementation Of Surface Impedance Boundary Conditions In FDTD

The finite-difference time-domain(FDTD)method in computational electromagnetics can calculate the electromagnetic field components at any time and location,providing an effective solution to the electromagnetic analysis of complex objects.However,when we use the traditional FDTD method to analyze the electromagnetic properties of a thin coating target,the thin coating needs to be finely meshed,resulting in a drastic increase in calculation time and memory usage.Therefore,the introduction of surface impedance boundary conditions(SIBC)is very necessary.We use the tangential field component of the coating surface to simulate its internal field distribution.This avoids the fine meshing of the thin coating.The traditional coarse meshing can be performed externally,which will greatly save computing time and reduce memory usage.Firstly,based on the first-order surface impedance boundary condition,the conformal surface impedance model of planar conductor structure and general smooth curved conductor structure is studied with the electromagnetic problem of the half lossy medium space as the entry point,and applied to the calculation of electromagnetic scattering.Subsequently,the SIBC-FDTD method for the coating of conductor targets with plane wave normal incidence and oblique incident lossy dielectric coating is studied in this paper.A simple rational approximation of the tangent function in the surface impedance formula is performed.The surface impedance is frequency-converted by the pull transformation.The frequency-domain-to time-domain conversion was deduced in detail,and the correctness of the method was verified by numerical tests.Compared with the traditional FDTD method,the computational efficiency was effectively improved.Then,taking the Lorentz dispersion model as an example,the SIBC-FDTD method for the target coated by dispersive medium on a vertically incident plane wave is studied.A continuous rational approximation of the tangent function is performed,and the convolution integral is iteratively calculated using a piecewise linear recursive convolution(PLRC)method.Then,it discretizes and derives the SIBC-FDTD iteration formula in three dimensions.The magnitude and phase of the reflection coefficient are calculated numerically,and error analysis is performed.Finally,the validity of Radar Cross Section(RCS)verification algorithm for thin-layer coating of two-dimensional metallic square columns is calculated.In summary,the SIBC-FDTD method discussed in this paper effectively solves the problem of sharp increase in computing time and memory usage due to the fine meshing when using the traditional FDTD method to handle complex thin coatings.The SIBC-FDTD method provides an effective solution to study the electromagnetic problem of complex targets.