Design and theoretical investigation of a switchable and tunable terahertz absorber based on graphene and vanadium dioxide

Abstract

This work proposes a switchable and tunable asymmetric cross-shaped terahertz metamaterial absorber, which employs a metal-dielectric-metal (MDM) structure, based on graphene and vanadium dioxide. A theoretical analysis of the absorber's absorption characteristics was conducted using the finite-difference time-domain (FDTD) technique, which indicates that the absorption of the absorber can dynamically switch between single band and triple band via VO₂ temperature-driven reversible insulator-to-metal phase transition. Specifically, the absorber exhibits single-band absorption above 90% from 1.45 to 4.13 THz in the VO₂ insulating state, while it exhibits triple-band absorption above 80% (covering 1.67–3.84, 7.13–8.26, and 12.07–12.75 THz) when VO₂ transitions to the metallic state. By tuning VO₂'s electrical conductivity and graphene's Fermi level, metasurface amplitude can be precisely adjusted. Additionally, impedance matching principles and transmission line theory were employed to analyze the absorber's operational mechanism. Finally, this study also examined the effect of polarization and incidence angle on absorption.