Switchable multifunctional metasurface based on vanadium dioxide absorbing and focusing at the same frequency

In this study, we proposed a switchable multifunctional terahertz metasurface based on vanadium dioxide, which can flexibly switch between absorbing and transmitting focusing. The design structure comprises the hybrid structure of vanadium dioxide and gold, vanadium dioxide film, and polyimide. Using the phase transition characteristics of vanadium dioxide and a reasonable layout of unit cells, the designed metasurface can absorb 97.5% and 99.4% of terahertz waves at 0.42 and 0.93 THz frequencies, respectively, under a vanadium dioxide–gold hybrid structure. In addition, the terahertz waves transmitted by the Fabry–Perot cavity, which is formed by consisting of two gold rings with diametrically opposite openings, can achieve polarization conversion and focusing effect at 0.93 THz frequency. The polarization conversion amplitude is up to 0.6. This study provides new ideas for designing multifunctional devices such as wavefront manipulation, focusing lenses, and stealth, and it has potential applications in terahertz imaging and communication.