I. Introduction
Considered as possible frequency band of 6G communication, the terahertz (THz) part of the electromagnetic spectrum, ranging from 0.1 to 10 THz, has found numerous potential applications researchers have been exploring the possible scheme for 6G communication in every aspect[1]. Fabry-Perot-interference (FPI effect)[13] has been mature in the field of optics, and has also been applied in the emerging field of metamaterials. Take Frequency Selective Surface FPI as an example, this paper will briefly introduce the FPI model and apply it to the principle analysis of the metamaterial converter designed in this paper to partially explain the significance of the air layer between the bilayer films for phase and amplitude modulation.There are many models for solving equivalent media, such as Maxwell-Wagner (MW) Hashin-Shtrikman (HS) Bruggeman Asymmetric(BA) and Bruggeman Symmetric (BS). Models. These models are based on the microstructure of individuals. The Brick-Layer (BL) model is also a way of representing the electromagnetic tensor of equivalent medium.