▎ 摘　　要

In this paper a quad-band, polarization-insensitive metamaterial perfect absorber (MPA) based on bi-layer graphene in the terahertz regime is presented. Initially, four models of the desired structure by using a single- layer graphene metasurface were examined. The results of the proposed four models show that two absorp- tion peaks were finally achieved at frequencies of 3.19 THz and 4.66 THz with the absorption of 99.61% and 99.95%, respectively. Then, by stacking the double layer graphene metasurface, a quad-band perfect absorber with an average absorption of 99.43% at the frequencies of 2.7 THz, 3.19 THz, 3.99 THz and 4.46 THz is ob- tained for 0.9 eV Fermi energy. Also, physical mechanisms of MPA have been studied by impedance matching theory. The study of the proposed structure with graphene metasurface has the advantage that the resonant frequency can be tunably adjusted without manufacturing again of the proposed structure. Furthermore, the proposed perfect absorber of metamaterial is polarization-insensitive and is more tolerant than the incident angle. The proposed absorber in this paper has potential in filtering, detection, imaging and other applications photodetectors, and other applications.