Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material

Abstract A terahertz absorber with controllable and switchable bandwidth that is insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO 2 ) and verify its performance by finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO 2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the insulator phase of VO 2 , the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon insulator-to-metal transition of VO 2 , the metasurface achieves a broadband absorption with FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase transition of VO 2 , we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to symmetry and works well for a very wide range of incident angles. In the metallic state of VO 2 , the absorber has an absorption exceeding 0.5 in the 3.57–8.45 THz frequency range with incident angles up to 65°.