Terahertz metamaterial absorber with switchable function between broadband and dual narrowband

In this paper, based on the tunability of vanadium dioxide and graphene, a simple and novel multifunctional terahertz metamaterial absorber is proposed that can dynamically switch functions and absorption spectra. The simulation results using the finite element method via Comsol Multiphysics show that the proposed design can achieve large broadband absorption, perfect dual narrowband absorption, and total reflection through controlling external conditions. The absorption intensity can be adjusted from 4.5% to 100% over the whole broadband operation range. A detailed absorption mechanism explanation is given with the help of impedance matching principles and the distribution of current and electric field, and the influence of graphene's Fermi level and different incidence angles on absorption performance is evaluated. Our design not only functionally adds the part to be a reflector but also provides considerable improvements in absorption amplitude, bandwidth, and adjustment range when compared to previous works. In addition, its function switching and resonant frequencies are flexible in terms of tuning and have strong resistance to external temperature interference. Therefore, the proposed structure holds significant applications in the terahertz field, such as terahertz modulators, sensing, and optical switches.