Broadband polarization-insensitive and oblique-incidence terahertz metamaterial absorber with multi-layered graphene

Metamaterial absorbers have been widely studied in the past decade and their performances have been incessantly improved in the practical applications. In this paper, we present a broadband terahertz metamaterial absorber based on graphene-polyimide composite structure, and the structure consists of a metal substrate and graphene layers with different sizes separated by two polyimide dielectric layers. The simulation results show that the absorptance of the absorber is greater than 90% in 0.86–3.54 THz with the fractional bandwidth of 121.8%. The absorptance can be adjusted by changing the chemical potential of graphene. In addition, the absorber is insensitive to polarization and still has robust tolerance for the oblique incidence. The equivalent circuit model based on transmission line is introduced to analyze the physics of the designed absorber and the results are in good agreement with the simulations. We believe that the designed absorber is a potential competitive candidate in terahertz energy harvesting and thermal emission.