Reconfigurable broadband polarisation conversion metasurface based on VO2

Abstract

Polarisation is an important characteristic parameter of electromagnetic waves. The controllable adjustment of the polarisation of electromagnetic waves is important for applications in fields such as antenna radiation, satellite communication, and radar stealth. In this study, a reconfigurable metasurface polarisation converter with a square ring structure and an opening was developed based on the reversible metal–insulator phase transition (MIT) of vanadium dioxide (VO2). VO2 is in the insulating high-resistance state (M phase) when its temperature is lower than the MIT temperature (68 °C). Finite element simulations showed that the metasurface could convert linearly polarised waves into cross-polarised reflected waves at frequencies of 8–18 GHz, corresponding to the X and Ku bands. The polarisation conversion rate (PCR) was over 90% and the relative bandwidth was up to 79%. VO2 is in the metallic low-resistance state (R phase) when its temperature is higher than the MIT temperature. At frequencies > 9.4 GHz, the PCR of the metasurface was less than 20%. Under these conditions, the polarisation of most of the reflected waves was the same as that of the incident wave. The polarisation converter was designed to work over a wide frequency range, and thus multiple resonances could be produced based on multiple resonance points in the working frequency range. Moreover, the electromagnetic wave component in the v-direction was rotated along 180°; hence, the polarisation of the incident electromagnetic wave rotated along 90°. When the resistance was low, the phases in the u- and v-directions were basically the same and the electromagnetic waves were reflected in the same direction. A smaller VO2 resistance denotes a higher co-polarisation reflection coefficient (Rxx). Rxx > 80% when the resistance of VO2 < 10 Ω, and Rxx > 90% when the resistance was 1 Ω. The maximum VO2 power loss was achieved when the resistance of VO2 was 188 Ω, i.e., the impedance matched with that of air. The experimental and simulation results were generally consistent. The proposed polarisation converter could have widespread applications in the dynamic control of electromagnetic waves, with uses in antenna radiation and radar cross-section reduction.