In this paper, a compact graphene-based penta-band terahertz (THz) absorber is proposed. The designed absorber is a three-layer structure including a graphene metasurface sheet, Topas-cyclic olefin copolymer dielectric substrate, and a gold ground plane. The absorption level and the resonant frequencies of the designed absorber may be tuned by adjusting the chemical potential of the graphene sheet. The electric and magnetic fields distributions of the graphene metasurface are investigated to better understand the physical mechanism of the absorption. Moreover, an equivalent circuit model is extracted based on the transmission line theory for the designed absorber. The corresponding results of the equivalent circuit model are compared to the full-wave simulation, which confirms the validity of the extracted circuit model. The suggested absorber is polarization-insensitive and the first three peaks are essentially unaffected by incidence angle changes up to 75 degrees and for both TE and TM modes. In comparison, two other peaks tolerate incidence angles up to 50 degrees. As a result, the proposed penta-band absorber will be an excellent choice for the design of multiband tunable absorbers with potential applications in optoelectronic devices.
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