Dual-band/ultra-broadband switchable terahertz metamaterial absorber based on vanadium dioxide and graphene

A dual-band/ultra-broadband switchable terahertz absorber based on vanadium dioxide (VO2) and graphene is proposed in this article. By controlling the properties of VO2 and graphene, the operation mode of the absorber can be switched between dual-band and ultra-wideband absorption. The simulation results show that the absorber works in the dual-band absorption mode when VO2 is in the insulating state and the Fermi energy level of graphene is 1.5 eV. The absorptivity are 99.4% and 99.8% at 1.08 and 3.52 THz, respectively. The frequency position of the absorption peaks can be switched by regulating the Fermi energy level of graphene. While the VO2 is transitioned to the metallic state and the Fermi energy level of graphene is 0.05 eV, the absorber operates in the ultra-broadband absorption mode with the absorptivity over 90% in the range 0.94- 4.31 THz, and the relative absorption bandwidth reaches 128%. In addition, the working principle of the proposed absorber is analyzed by impedance matching theory and electric field distribution. Based on these characteristics, the proposed metamaterial absorber is expected to be used in the terahertz bio-detection and imaging fields.