Design of a graphene-based multi-band metamaterial perfect absorber in THz frequency region for refractive index sensing

In this paper, a multi-band metamaterial perfect absorber, formed by an array of combined H and U-shaped graphene stripes, is proposed. The structure is numerically simulated using the finite element method. The simulation results show that if the graphene layer's chemical potential is equal to 0.9eV, three absorption peaks are found in the proposed system's transmission spectrum at frequencies of 5.29, 6.76, and 9.1 THz with ab-sorption coefficients of 99%, 99.8%, and 86%, respectively. Using an external DC-bias voltage which changes the chemical potential of the graphene layer, the absorption spectra of the combined absorber can be adjusted. It is also shown that the proposed absorber can act as a good refractive index sensor, with a maximum sensitivity of 1783 GHz/RIU, where RIU stands for the refractive index unit. Based on the simulation results, the proposed absorber appears to be a good candidate for applications such as biochemical sensing.