Polarization Insensitive Graphene Based Tunable Metasurface Terahertz Dual-Band Absorber

This article presents an electronically tunable metasurface wideband absorber with a graphene-based unit cell designed for the lower terahertz (0.1 THz– 10 THz) region. Surface plasmonics and the controllable conductance of graphene make it ideal for this purpose. Dual wideband absorption ( $ >$ 90% absorptivity) was observed from 0.682 to 1.798 THz (90% fractional bandwidth) and 4.187 to 4.947 THz (16% fractional bandwidth). The absorber is insensitive to polarizations and oblique incidences up to 45°. The unit cell comprises a double elliptical-cross graphene monolayer on a polyimide substrate (dielectric constant: 3.5, loss tangent: 0.0024) backed by an ultra-thin gold layer. Plasmonic resonance, introduced by four semicircular slots, causes absorption from 4.15 to 4.95 THz. Absorption properties were verified through a transmission line model and finite element method (FEM) simulations. Tunability is investigated via gating potential, carrier relaxation time, and Fermi energy variations.