Design of a Metafilm-Composite Dielectric Shielding Structure using a Genetic Algorithm

An analytical model for a shielding structure containing both bulk composite layers and planar metafilms (MFs) made of perfect electric conductors is presented, allowing for synthesis of shielding structures using the genetic algorithm (GA) optimization. MFs can be of two different types: patch or aperture. The frequency response, specifically, transmission (T) and reflection (Γ) coefficients in a plane-wave formulation, of any MF is calculated based on polarizabilities determined by the particular pattern geometry. T and Γ of a patch-type MF are derived using the generalized sheet transition conditions (GSTC) and the Babinet's duality principle is used for aperture-type MF to map the results from the complementary problem. T and Γ for a single layered MF are represented in a unified matrix form for any angle of incidence. T-matrix approach is used for getting T and T for a multilayered structure. Any MF buried in a host dielectric can be decomposed into three types of basic elements: a host composite slab, interface between media, and an MF inside the homogeneous host medium. Each basic element is described by a corresponding T-matrix, and the total T-matrix of the stack is the sequential product of the each individual T-matrix. T and Γ of the stack can be easily derived from the total T-matrix. If there are two or more MFs, the distance between them justifies the condition of neglecting higher-order evanescent mode interactions. Then the GA is applied to engineer a structure with the desired frequency response. It helps to choose the best geometry of MF patterns, thickness of layers, and appropriate constitutive parameters of each composite layer.