Multifunctional and tunable terahertz coding metasurfaces based on vanadium dioxide

Metasurfaces play a pivotal role in terahertz wave modulation and control. However, persistent challenges in metasurface development include non-reusability and the complexity of structural adjustments. In this paper, we present a solution: a multifunctional tunable coding metasurface combined with a phase change material (PCM) utilizing vanadium dioxide (VO2). Initially, we design 1-bit coding metasurfaces based on phase gradients, enabling dual-beam and four-beam reflection. Building on this, we develop 2-bit coding metasurfaces, enabling anomalous reflection of a single beam in four distinct directions. Subsequent implementation of binary addition further expands the azimuthal angle of the reflected wave to encompass eight directions. Notably, by modulating the conductivity of vanadium dioxide, the single-state coding metasurface transition from phase regulation to amplitude regulation. This transition leads to absorption resonance frequencies at 0.35 THz, 0.39 THz, 0.47 THz, and 0.66 THz, achieving absorption rates exceeding 90%. As a result, these multifunctional coding metasurfaces seamlessly integrate electromagnetic wave amplitude and phase control techniques. They boast a straightforward yet powerful structure, demonstrating exceptional reusability and adjustable configurability for the metasurfaces.