Conjugate Adjoint Gradient-Based Inverse Design Method for Aperiodic Frequency-Selective Surface With Weighted Loss

Multifunctional frequency-selective surfaces (FSSs) provide many possibilities for controlling electromagnetic waves as well as for reducing electromagnetic interferences (EMIs). However, for most aperiodic FSSs, their forward simulations and inverse designs are extremely time and memory consuming. In contrast to tuning computationally expensive forward models, we propose a conjugate adjoint gradient-based inverse design method (CAG-IDM) for aperiodic FSS structures in which both forward solver and inverse design method are included. Specifically, the proposed forward method generates far-field distribution based on local equivalent sources with dyadic Green's function by a far-field solver. Meanwhile, the local equivalent sources are computed by local periodic approximation with a local solver. Furthermore, the inverse design process utilizes conjugate adjoint gradient method to accelerate the inverse process in which the derivative of the loss with respect to the design structure parameters is computed. The proposed forward method is numerically verified by comparing with commonly used commercial software. To further verify the proposed method, an aperiodic multifunctional FSS is inversely designed by the proposed CAG-IDM, where the fabricated FSS has the properties of low-frequency EMI absorption, midfrequency transmission, and high-frequency scattering.