Theoretical investigation of a tunable vanadium dioxide-based metastructure for ultra-wideband absorption and linear-to-circular polarization conversion across triple-octave frequencies

, the MS is shown to operate as a converter tripling the octave frequency in linear-to-circular polarization, with an axial ratio below 3 dB across the frequency ranges of 0.95-1.68 THz and 2.25-4.49 THz, corresponding to relative bandwidths of 55.51% and 66.27%. Remarkably, the polarization conversion in the insulating state exhibits tripling octave frequency characteristics, with a fundamental bandwidth spanning 0.95-1.49 THz and a tripling octave frequency bandwidth spanning 2.85-4.48 THz. The MS can switch between distinct functionalities within the terahertz regime, offering significant potential for applications such as spectral analysis, signal encryption, stealth material preparation, and other advanced terahertz technologies.