Multifunctional voltage and temperature controlled metasurface using graphene and vanadium dioxide for terahertz applications

Abstract

This paper presents a metasurface with multiple functionalities designed for terahertz (THz) frequency applications, utilizing graphene and vanadium dioxide (VO₂). The proposed metasurface is controllable through the voltage-tuning properties of graphene and the temperature-tuning properties of VO₂. The unit cell is comprised of a silicon dioxide (SiO₂) substrate and reflective ground made of gold. The top layer is composed of a diagonally connected split hexagon (DCSH) made using the combination of graphene and VO₂. In normal room temperature (298 K), i.e., at the insulating state of VO₂, the metasurface operates as a linear-to-linear cross polarization converter (LTLPC) for the frequency band 1.61 THz to 1.88 THz, i.e., 15.47% fractional bandwidth (FBW) and a linear-to-circular polarization converter (LTCPC) from 2.46 THz to 3.10 THz, i.e., 23% FBW and a triple band absorber with absorption maxima at 1.51 THz, 2.52 THz, and 3.59 THz having 100%, 99.3%, and 84.3% absorptions, respectively. In higher temperatures (above 351 K), i.e., in the metallic state of VO₂, the metasurface operates as an LTLPC for the frequency band 1.60 THz to 3.26 THz, i.e., 68.31% FBW, and a dual-band absorbers at frequency at 1.50 THz and, 3.31 THz with 100% and 99.2% absorptions. The equivalent circuit models of the metasurface are presented for insulating and metallic states. The device's performance exhibits uniformity of response up to 40° incident angle variations for the insulating state as well as for the metallic state of VO₂. It offers excellent dynamic switching capability, versatile tunability, and multimodal operations for terahertz applications.