A switchable and adjustable terahertz absorber using vanadium dioxide and graphene

We propose a versatile tunable terahertz (THz) absorber based on vanadium dioxide (VO2) and graphene, and studied the absorption properties of absorber using the finite difference time domain (FDTD) method. It was found that by adjusting the conductivity of VO2 via temperature, the absorber can exhibit narrowband or wideband absorption. When the VO2 is kept in room temperature it has low conductivity and is in insulating state, the absorber operates in a narrowband absorption mode. When the temperature of VO2 is higher than 68 °C it is in the metallic state, the absorber shows a wideband absorption. In addition, the amplitude of absorption can be adjusted easily by changing the Fermi energy level (EF) of graphene. When the VO2 is in insulating state,and the EF of graphene is set at 1.2 eV, the terahertz absorber shows a strongest narrowband absorption with a peak at 5.25 THz. When the VO2 is in metallic state,the terahertz absorber can achieve wideband absorption exceeding 90 % in 1.48–3.62 THz range. Furthermore, we analyzed the absorption mechanism of the absorber using impedance matching theory and transmission line theory, and investigated the influence of incident angle on absorption spectra. Finally, we validated the capability of metasurfaces as a biosensor by detecting avian influenza viruses.