▎ 摘　　要

A tunable hybrid metal-graphene frequency selective surface (FSS) based on split-ring resonators at mid-infrared frequencies is proposed and numerically investigated by an improved leapfrog alternating direction implicit (ADI)-finite-difference time-domain (FDTD) method. The graphene conductivity described by a new closed-form approximate expression is incorporated into the leapfrog ADI-FDTD through the vector-fitting technique and auxiliary differential equation approach. Numerical simulations show that the proposed method has good computational accuracy and higher efficiency compared to conventional FDTD method and analytical solutions. Besides, the transmission and reflection coefficients of the FSS can be effectively adjusted by changing the chemical potential of graphene, the layer number of graphene patch and operating temperature. This work provides a novel method for designing tunable devices for optical plasmonic applications.