A continuous-graphene terahertz absorber exhibiting ultra-broadband and multi-band high absorption

In this paper, an ultra-broadband terahertz (THz) metamaterial absorber based on multiple resonant contributions is proposed and numerically investigated. The structure consists of a continuous (non-patterned) graphene sheet integrated with a dielectric spacer, a cylindrical silicon resonator, and a metallic ground plane. Unlike conventional graphene-based absorbers that rely on patterned graphene to achieve resonance, the present design employs a continuous graphene layer, where the absorption arises from the coupling between the dielectric cavity modes, resonant response of the cylindrical silicon resonator, and the Fermi-level-dependent surface conductivity of graphene. Full-wave numerical simulations reveal the formation of three distinct absorption regions: a low-frequency narrowband response from 2.04 to 2.38 THz (BW = 0.34 THz), an ultra-broadband absorption band spanning 3.79‒10.12 THz (BW = 6.33 THz), and a high-frequency narrowband response from 11.26 to 11.60 THz (BW = 0.34 THz), all exhibiting absorptance exceeding 90%. The broadband response is associated with overlapping resonant contributions within the dielectric cavity and the silicon resonator, rather than any geometrical patterning of graphene. Due to the structural symmetry, the absorber exhibits polarization-insensitive behavior at normal incidence and maintains high absorption up to 25° for TE polarization and 45° for TM polarization. Furthermore, absorption modulation is achieved by varying the Fermi level of graphene, enabling dynamic adjustment of the absorption characteristics without altering the physical structure. The proposed structure provides a structurally accessible platform for studying broadband absorption in continuous-graphene configurations and may be of interest for THz device applications.