Equivalent circuit model for the analysis and design of graphene-based tunable terahertz polarizing metasurfaces

In this work, we present an equivalent circuit model that facilitates the analysis and design of graphene-based transmission- and reflection-mode tunable terahertz polarizers. The conditions for polarization conversion are analytically derived, and a set of closed-form design formulas is presented. Given the target specifications, the key structural parameters are directly calculated. The proposed method is rigorously validated for two linear-to-circular polarizers operating in transmission and reflection modes. The results from the circuit model and full-wave electromagnetic simulation are compared, and excellent agreement is observed. The proposed circuit model is accurate and effective, and speeds up the analysis and design processes. The polarizers studied in the present work feature simple geometries and competitive performance with respect to other metasurface polarizers. The tunable fractional bandwidths, over which linear-to-circular polarization conversion is achieved, by varying the graphene chemical potential, are 65% and 36%, respectively, for the two transmission- and reflection-mode polarizers.