▎ 摘　　要

In this paper, a novel configuration of a tunable ultra-broadband terahertz (THz) absorber based on two layers of graphene ribbons and two different kinds of substrate materials has been proposed. The recently suggested equivalent circuit theory of Periodic Arrays of Graphene Ribbons (PAGRs) with a developed transmission line model is utilized to design the structure of the THz absorber. Also, an equivalent series RLC branch is considered for each layer of PAGRs. By adopting the impedance matching approach, the real part of the input impedance of the proposed structure is tuned to be approximately matched to the free-space impedance in a wideband THz region. Then, the imaginary part of the input impedance is adjusted to near zero around the central frequency for increasing the proposed absorber's bandwidth. As a result, the normalized bandwidth of 70% absorption has reached up to 118% with only just two layers of graphene ribbons. Based on the purpose of this paper, the bandwidth of the proposed absorber has been controlled by the chemical potentials of the graphene ribbons.