Demonstration of Thermally Tunable Multi-Band and Ultra-Broadband Metamaterial Absorbers Maintaining High Efficiency during Tuning Process.

Metamaterial absorbers (MMAs) with dynamic tuning features have attracted great attention recently, but most realizations to date have suffered from a decay in absorptivity as the working frequency shifts. Here, thermally tunable multi-band and ultra-broadband MMAs based on vanadium dioxide (VO) are proposed, with nearly no reduction in absorption during the tuning process. Simulations demonstrated that the proposed design can be switched between two independently designable multi-band frequency ranges, with the absorptivity being maintained above 99.8%. Moreover, via designing multiple adjacent absorption spectra, an ultra-broadband switchable MMA that maintains high absorptivity during the tuning process is also demonstrated. Raising the ambient temperature from 298 K to 358 K, the broadband absorptive range shifts from 1.194-2.325 THz to 0.398-1.356 THz, while the absorptivity remains above 90%. This method has potential for THz communication, smart filtering, detecting, imaging, and so forth.