Actively tunable multi-frequency narrowband terahertz absorber using graphene metamaterials

Abstract

This study presents a novel design for a multi-frequency narrowband terahertz absorber utilizing graphene metamaterials. Unlike other graphene-based terahertz absorbers, the proposed structure eliminates the need for graphene patterning, significantly simplifying the fabrication process and enhancing its feasibility for practical applications. The absorber consists of four layers: an Au substrate, a dielectric layer, a graphene layer, and a patterned Au absorption layer. The pattern of the metasurface absorption layer is composed of four rotationally symmetric rectangles and rings, which achieve high absorption performance while eliminating the need for graphene patterning. The simulation results indicate that when the terahertz wave strikes the absorber at a perpendicular angle and the graphene Fermi level is adjusted to 0.1 eV, the absorber achieves near-perfect absorption at five frequencies: 4.4362 THz, 6.4261 THz, 7.1191 THz, 9.1981 THz, and 9.604 THz, with a maximum absorption rate of 99.828 %. By determining the relative impedance of the absorber using the parameter inversion method through simulation, it is observed that the absorber follows the impedance matching theory. Moreover, through the study of the electric field distribution corresponding to the absorption peak, it is found that when the terahertz wave is incident on the absorber, a high absorption effect is produced due to the localized surface plasmon resonance (LSPR) between the Au layer and the graphene layer on the surface, LSPR technology has been widely utilized in applications such as sensors and absorbers. Furthermore, by adjusting the Fermi level of graphene and analyzing the absorption spectrum, it is demonstrated that the Fermi level enables active tunability of the absorber, highlighting its potential value in the field of terahertz smart devices.