▎ 摘　　要

A mixed finite-element method with an impedance transmission boundary condition (ITBC) is proposed to solve the graphene plasmonicmodes. The new variational formulation combines the Gauss' law with the transverse components of vectorial Helmholtz equation and models the field penetration through a thin graphene sheet by ITBC. The second-order edge-based vector LT/QN basis functions are applied to expand the transverse components of the electric field, and the nodal-based scalar basis functions are employed to discretize its longitudinal component. Numerical results on some designed graphene-based waveguides clearly demonstrate that the proposed method is efficient and accurate for the determination of graphene plasmonic modes.