Retrievals For Equivalent Electromagnetic Parameters Of Metamaterial Slabs With Improved Method

Metamaterials have received considerable attention after D. R. Smith realized negative index material by experiment. The characteristic and application have been deeply and widely researched due to the especial property.Metamaterials are generally composed of subwavelength resonant unit cells mimicking the response of molecules or atoms to electromagnetic waves. The typical metamaterial particles are structured by split-ring resonators (SRRs) and electric-field-coupled inductance capacitance resonators (ELC), which are inspired by magnetic and electric fields, respectively. The responses of SRR and ELC are often characterized by effective medium parameters, i.e., the electric permittivityεand the magnetic permeabilityμ. One of the commonly adopted approaches to determine such parameters is to compare the calculated or measured transmission and reflection coefficients of a metamaterial slab with a certain thickness to the analytical expression of a homogeneous slab of the same thickness, which is the so-called the S-parameter retrieval.In the past few years, there have been various other approaches to reach the same goal. The problem is, though metamaterials are effective media, the metamaterial particles are strongly resonant and have subwavelength sizes which lead to the inherent coupling between neighboring particles.In the process of S-parameter retrieval, it is assumed that all particles in a metamaterial slab exhibit the same response to the applied field, which is only an approximation due to the existing coupling. The dissimilarity of coupling effects between edge and inner cells in a metamaterial slab is thus considered by author and advanced parameter retrievals using an inhomogeneous medium model are proposed. It shows that the effective medium parameters for edge and inner cells are different, which results in the inhomogeneous property of the metamaterial slab. The retrieval methods have been presented to obtain the effective medium parameters of edge and inner cells by considering two- and three-cell metamaterial slabs, respectively, from which an inhomogeneous three-layer model is set up for arbitrary metamaterial slabs. The numerical simulations verify the accuracy of the proposed inhomogeneous model.It is very useful for theoretical calculations and analysis design of massive periodic structures. Based on it, the design of optical transfer device is more accurate and efficiency, such as cloak, concentrator, lens and so on.