A broadband and switchable VO2-based perfect absorber at the THz frequency

We demonstrate a broadband and switchable THz metamaterial absorber by utilizing the phase transition of VO2, which is a stacked structure composed of VO2 periodic array, dielectric layer, VO2 film, Au periodic array, dielectric layer and Au reflective layer, respectively. The absorption band from 0.76 THz to 0.86 THz at room temperature can be changed into the absorption band from 1.12 THz to 1.25 THz when temperature increases above the phase change temperature of VO2, with the absorptivity in both bands over 90%. Furthermore, the effective medium theory is introduced to explain the perfect absorption mechanism. Such absorber can work well over a wide range of incidence around 40 degrees. Thickness of the absorber is only about one twentieth of the working wavelength. The proposed structure can be applied to absorbers working at other frequencies.