层状介质时域有限差分方法斜入射平面波引入新方式

New scheme for introducing an oblique incidence plane wave to layered media in finite-difference time-domain

应用二维时域有限差分方法分析层状介质中的目标散射时,在总场-散射场边界斜入射平面波源用常规方法难以引入,因为在总场-散射场边界处设置的入射波实际上包含了入射脉冲以及各分层界面的反射和多次反射.为解决这个问题,提出了斜入射平面波的混合引入方式,即对总场-散射场的四个边界面采取不同的处理方式.对于总场-散射场的纵向侧边界,用含有斜入射角度的修正一维时域有限差分方法,只要在自由空间位置加入入射脉冲就会自行产生由各分层界面形成的反射波,包括多次反射.同时,把纵向总场-散射场侧边界向下延伸,使得总场-散射场下边界位于完全匹配层内,这样透射波和散射波均为外向行波而被吸收.对于总场-散射场的上边界,由于完全位于自由空间中,边界上各点的入射波将是总场-散射场纵向边界角点处入射波的带有时间延迟的复制.数值模拟结果表明了本文所提出方法的正确性和有效性.

In the application of two-dimensional finite-difference time-domain （2D-FDTD） method to the analysis of scattering by an object embedded in layered media, the obliquely incident wave along the total field-scattered field （TF-SF） contains the incidence pulse and the reflected and multiple-reflected wave,which can not be introduced by use of the traditional method. To solve this problem, a hybrid scheme using different ways to treat the four TF-SF boundaries is presented. The modified 1D-FDTD including oblique incidence angle is used to treat the longitudinal side boundaries, which can produce the reflected and multiple-reflected wave to layered interface automatically. The longitudinal side boundaries are extended downwards, such that the TF-SF lower boundary is located in the perfectly matched layer （PML） completely, thus the transmission wave and scattered wave arc both outward-going waves in the lowest PML layer, and are absorbed by PML. The TF-SF upper boundary is located in free space; the incidence wave along it is in fact a properly time-delayed duplication of the waveform at the corner of TF-SF upper longitudinal boundary. The computational results show the reliability and applicability of the presented hybrid scheme.