Bifunctional Metamaterial for Broadband Absorption and Cross-polarization Conversion Based on Vanadium Dioxide in Terahertz Band

In this paper, a switchable bifunctional metamaterial with broadband absorption and cross-polarization conversion properties in the terahertz band is proposed based on the phase transition properties of vanadium dioxide (VO2). When VO2is in the metallic state, the metamaterial structure exhibits the function of broadband absorption in the terahertz band. The absorber consists of a VO2top structure, a Polyethylene cycloolefin copolymer (ToPaS) dielectric layer, and a VO2film. The absorption rate of metamaterial absorber is more than 90% in the range of 2.51-6.51THz. The absorber is insensitive to the polarization mode of the incident electromagnetic wave due to the rotational symmetry of the unit structure, and still has good absorption stability in the case of large angle incidence. When vanadium dioxide is in the insulating state, metamaterials perform the function of broadband polarization conversion. The polarization converter is composed of a gold strip, a ToPaS dielectric layer and a gold substrate. The numerical results show that the polarization conversion efficiency is more than 90% in the range of 1.42-2.59 THz. In addition, the polarization conversion performance can still be achieved for oblique incident electromagnetic waves. The designed structure has potential application prospects in terahertz stealth, radar, communications and other fields.