Switchable and tunable terahertz metamaterial absorber with broadband and multi-band absorption

In this paper, we propose and demonstrate a switchable terahertz metamaterial absorber with broadband and multi-band absorption based on a simple configuration of graphene and vanadium dioxide (VO₂). The switchable functional characteristics of the absorber can be achieved by changing the phase transition property of VO₂. When VO₂ is insulating, the device acts as a broadband absorber with absorbance greater than 90% under normal incidence from 1.06 THz to 2.58 THz. The broadband absorber exhibits excellent absorption performance under a wide range of incident and polarization angles for TE and TM polarizations. Moreover, the absorption bandwidth and intensity of the absorber can be dynamically adjusted by changing the Fermi energy level of graphene. When VO₂ is in the conducting state, the designed metamaterial device acts as a multi-band absorber with absorption frequencies at 1 THz, 2.45 THz, and 2.82 THz. The multi-band absorption is achieved owing to the fundamental resonant modes of the graphene ring sheet, VO₂ hollow ring patch, and coupling interaction between them. Moreover, the multi-band absorber is insensitive to polarization and incident angles for TE and TM polarizations, and the three resonance frequencies can be reconfigured by changing the Fermi energy level of graphene. Our designed device exhibits the merits of bi-functionality and a simple configuration, which is very attractive for potential terahertz applications such as intelligent attenuators, reflectors, and spatial modulators.