Ultra-wideband and multi-frequency switchable terahertz absorber based on vanadium dioxide

In this paper, we present the design of a switchable terahertz absorber utilizing vanadium dioxide. The switching from ultra-wideband absorption to multi-frequency absorption is achieved by adjusting the conductivity of vanadium dioxide via temperature control. Specifically, when the conductivity of vanadium dioxide reaches 2 x 105 S/m, the absorber demonstrates an absorption bandwidth of 5.4 THz, attaining an absorption rate of 90 % within the frequency range of 3.9-9.3 THz. Conversely, at a conductivity level of 20 S/m, the absorber exhibits multi-frequency absorption characteristics, revealing four distinct absorption peaks, all surpassing 90 % absorption rate, located at frequencies of 3.94 THz, 7.06 THz, 7.7 THz, and 9.16 THz, respectively. To elucidate the underlying physical mechanisms governing these two distinct absorption modes, we utilize the impedance matching theory and conduct an analysis of the distribution of electric field energy. Furthermore, the absorber exhibits polarization insensitivity and maintains effective performance across a broad spectrum of incident angles, ranging from 0 to 80 degrees. The designed absorber holds significant potential for application in terahertz imaging, sensor technology, communications, and the optoelectronic industry.