Theoretical research on a switchable trifunctional broadband terahertz absorber based on graphene and vanadium dioxide resonators

The development of broadband perfect absorbers with tunable absorption, multiple broadband capabilities, and versatile switching functionalities remains a significant challenge in the field of metamaterials. In this paper, we propose a switchable trifunctional broadband terahertz (THz) absorber based on a hybrid structure of graphene and vanadium dioxide (VO2) resonators. When VO2 is in its insulating state with a conductivity of 200 S/m and the Fermi energy of graphene is set to 0.9 eV, the structure operates as a low-frequency single-broadband absorber, achieving over 90 % absorption in the frequency range of 0.48-2.10 THz, corresponding to a fractional bandwidth of 125.6 %. Remarkably, the functionality of the absorber can be dynamically adjusted. For instance, when the Fermi energy of graphene is fixed at 0.01 eV and the conductivity of VO2 is increased to 1 x 104 S/m, the structure functions as a dual-broadband absorber, exhibiting over 90 % absorption in two distinct frequency ranges: 0.64-2.02 THz and 3.23-4.57 THz, with fractional bandwidths of 100 % and 33.6 %, respectively. Further increasing the conductivity of VO2 to 2 x 105 S/m transforms the absorber into a high-frequency single-broadband absorber, covering a broad frequency range of 0.94-4.56 THz with a fractional bandwidth of 131.6 %. Additionally, the proposed absorber exhibits angle-insensitive absorption properties, making it a promising candidate for applications in thermal emitters, detectors, and tunable absorption filters.