Tunable wide band near-perfect absorber for terahertz waves based on a vanadium dioxide metasurface

Vanadium dioxide (VO₂) is a remarkable phase-change material whose temperature-driven insulator-to-metal transition unlocks powerful tunability in the THz regime. Here, we present a VO₂-based metasurface that not only achieves over 90% absorption efficiency across a broad 1.27–2.64 THz range when in its metallic phase, but also transitions into a nearly perfect reflector (0.1–4 THz) in its dielectric phase. This striking dual functionality leverages the unique conductivity variation of VO₂ with temperature and is realized through a metasurface on a thin SiO₂ spacer backed by a gold layer. Notably, our design maintains insensitivity to both polarizations and incidence angle—crucial characteristics for practical THz applications—while offering a robust, wideband response. Through systematic analysis, we elucidate the physical mechanisms governing the high absorption and reflection, and demonstrate how key geometric parameters influence the device performance. By combining wideband tunability, angular and polarization invariance, and design simplicity, this metasurface holds substantial promise as a versatile component for next-generation THz technologies.