Tunable quad-band perfect metamaterial absorber on the basis of monolayer graphene pattern and its sensing application

Abstract

In this paper, a classic three-layer metamaterial absorber (MA) is designed to achieve quad-band perfect absorption. The unit cell of the top graphene pattern layer is made up of a periodically arranged graphene split-ring nested with a cross-like graphene structure formed by four L-shaped strips. The middle dielectric spacer layer is SiO2 and the ground layer is gold. Simulation results show that four absorption bands with near unity peak absorption rate will occur in the interested frequency range of 3–11 THz. The absorption mechanism and the parameter dependency are discussed at first, which will provide guiding significances for the actual fabrication. Meanwhile, when the Fermi level of graphene is increased, the four absorption bands will have different degrees of blue-shift, and when the relaxation time of graphene is increased, the four absorption peaks will increase first and then decreases. As a result, dynamical tunability of the absorption properties can be achieved by changing the Fermi level or the relaxation time of the graphene without changing the geometry of the proposed MA. Further investigation indicates that the proposed absorber is independent of the polarization of the input electromagnetic (EM) wave and can maintain well absorption properties when the incident angle is changed within a broader range. Considering the potential sensing applications, it is shown that the proposed MA can be operated as a type of refractive index sensor with highest sensitivity of 2.97THz/RIU, and the maximum figure of merit (FOM) is 47.5. In terms of these unique performances, the proposed MA has broad application prospects in multispectral optical stealth, optical filtering, integrated photo detecting, sensing and so on.