A broad/narrow band switchable far-infrared dual-functional absorber based on vanadium dioxide and graphene

In this work, we present a metamaterial perfect absorber (MPA) for the far-infrared band that leverages the phase transition in vanadium dioxide (VO₂) to achieve a dynamically switchable response, alternating between broadband and narrowband absorption. The structure, from bottom to top, consists of a Ti substrate, a Si dielectric layer, a two-dimensional graphene (GE) layer, and a patterned VO₂ layer. When VO₂ is in the metallic state, the structure exhibits broadband absorption, covering 16.7 to 28.7 THz with an average absorption rate of 96.1%. We analyze its physical mechanism through the distribution of electromagnetic fields. When VO₂ is in the insulating phase, the proposed MPA exhibits nine distinct absorption peaks, each exceeding 90% absorption, and demonstrates excellent sensing characteristics, with the highest sensitivity reaching 3.978 THz/RIU. Our design offers the advantages of numerous narrowband absorption peaks, high sensitivity, and wide bandwidth. Additionally, this MPA can be tuned to achieve functional switching over a small range of conductivity changes. Therefore, our design has important applications in sensing, optical switching, energy harvesting, and remote sensing.