Dynamically switchable multifunctional device for terahertz application using vanadium dioxide and graphene-based metasurface

Abstract In this article, a dynamically switchable and multifunctional metasurface is realized using a combination of vanadium dioxide (VO2) and graphene-based structures. The device can be tuned using the temperature transition property of vanadium dioxide from a wideband linear-to-circular polarization converter (LTCPC) to a wideband linear-to-linear cross polarization converter (LTLPC) and a dual-band absorber. The unit cell is designed with a gold-backed lossy-silicon dioxide (SiO2) substrate with a permittivity of 3.9, and the top metasurface layer is designed with a graphene-based dual triangle loaded split ring (DTLSR) and two stripes of vanadium oxide to cover the split partially. The proposed device can be used as a wideband LTCPC at normal temperature (298 K) from 1.43 THz to 2.85 THz, i.e., 66.35% fractional bandwidth (FBW). At temperatures greater than 341 K, VO 2 exhibits metallic properties, and the structure functions as LTLPC from 1.82 THz to 3.31 THz (PCR ≥ 80%), i.e., 58.08% FBW and maximum polarization conversion ratio (PCR) reported as high as 99.65%. Furthermore, at this metallic condition, two absorption peaks are obtained at 1.22 THz and 3.30 THz with absorptivity of 93.5% and 100%, respectively. The device offers incident angle invariability up to 40° for LTCPC and up to 50° for LTLPC operation. Further insight into the mechanism of operation is developed using the surface current density and electric field distribution analysis. The advantage of the proposed metasurface over other similar structures is assessed with respect to multifunctional behavior, bandwidth, and stability under oblique incidence.