Design of graphene-based tunable ultra-thin UWB metasurface for terahertz regime

Abstract

This work presents a simple graphene-based tunable ultra-wideband (UWB) metasurface for terahertz application. The unit cell comprises a silicon dioxide (SiO2) substrate sandwiched between the top patterned graphene layer and the bottom continuous graphene layer, where each graphene layer is 1 nm thick. A separate DC bias configuration is also introduced, consisting of another SiO2 substrate backed by a gold plate to achieve independent biasing of both graphene layers. The metasurface is ultra-thin with a thickness of only 5.1μm, i.e. λ0588.235, where λ0 is calculated at the lowest operating frequency. The proposed absorber provides an absorption bandwidth (BW) of 13.9 THz (Fractional BW = 197.16%), covering the electromagnetic spectrum from 0.1 to 14 THz with an absorptivity of more than 90%. The periodicity of the proposed unit cell is found to be only 13.5μm, i.e. λ0222.22. Hence, it satisfies the effective homogeneity condition. The designed unit cell has structural symmetry, which makes the proposed absorber polarization insensitive to the normal incidence of the plane wave. The structure is also examined under a different incident angle (θ) for both TE and TM polarization. It is found to have absorptivity of more than 80% in the frequency range 0.1–14 THz for incidence angle up to 60∘. The variation in the chemical potential (μc) of top Gpat provides tunable absorption characteristic. The increase in μc of Gpat leads to the blue shift in the absorptivity response. The proposed absorber covers the entire ”Terahertz Gap” of the electromagnetic spectrum and is suitable for various terahertz regime applications.