Brewster operated electrically tunable graphene–metal hybrid resonator-based ultra-thin THz multiband absorber

A hybrid of a non-resonating graphene sheet and metallic resonators is utilized to make an ultra-thin terahertz (THz) absorber. Hybridizing graphene with metal helps in confining the incident electromagnetic (EM) field to develop the ultra-thin geometry of the absorber with a thickness of ≈ λ /206 ( λ is the free space wavelength). The coupled EM resonance in the hybrid resonance structure results in ultra-thin geometry, which usually remains difficult in the case of a Fabry–Perot cavity. The EM resonance taking place in the metallic resonators can provide the four narrow absorption bands with more than 80% absorption. The response of the absorber can be tuned using electrically operated graphene’s conductivity. The count of the absorption peaks can be incremented to eight by Brewster’s effect for incident TM polarized waves. The frequency response of the proposed absorber is validated using electrical circuit analysis. Moreover, the resonances can be excited with ultranarrow full-width, half-maxima, which can make the absorber structure capable for THz refractive index sensing. The proposed absorber can provide ultra-sensitivity of up to 0.6 THz/RIU with a high quality factor of 228.