▎ 摘　　要

An improved 1-step leapfrog hybrid implicit-explicit finite-difference time domain method is developed for simulating tunable characteristics of graphene metasurfaces over an ultrawide terahertz band for different physical and geometrical parameters. The graphene conductivity is described by a closed-form approximate expression and further expanded into a rational sum of complex-conjugate pole-residue pairs using the vector-fitting technique. It is further implemented into the leapfrog hybrid implicit-explicit finite-difference time domain by an associated auxiliary differential equation formulation. Parametric studies are performed for capturing terahertz band responses of some typical graphene metasurfaces, with their tunabilities investigated and compared for different chemical potentials, layer numbers of graphene surface, operating temperatures, etc. When the results are compared with conventional finite-difference time domain and analytical solutions, the proposed method demonstrates both high efficiency and good accuracy.