Design of tunable dual-gas sensor based on phase transition of VO2 in Metasurface

A tunable dual-gas sensor based on VO2 is proposed, and the metasurface is composed of a multi-layer metal-dielectricmetal (MDM) structure. The first to six layers of the structure are VO2 cylinder, methane sensitive film, VO2 film, gold square ring, hydrogen sensitive film, and gold film. The conductance coupling between the metal structures can be manipulated by the metal-insulator phase transition of VO2 to change the LSPR resonance mode. The transformation realizes active tunable dual-gas detecting of the methane and hydrogen, and the effects of structural parameters and polarization mode on the frequency response characteristics of the structure are investigated respectively. Subsequently, a theoretical study of the active adjustable dual gas sensor was carried out. When the temperature exceeds the phase transition temperature of VO2 (T>68 degrees C), VO 2 exhibits metallic properties and excites resonant coupling at 1647.4nm. At this time, methane-gas detection is realized and the absorption rate of the sensor reaches 92%, which is not only because of the VO2 cylindrical surface resonance but more electric energy is localized in the methane-sensitive film. The sensor realizes hydrogen detection when VO2 is in an insulated state (T <= 68 degrees C), the incident light penetrates the upper three-layer structure and matches the plasma frequency of the lower three-layer MDM structure to excite resonance at 2191.4nm. However, the energy of the incident light is lost through the upper three-layer structure, which causes the absorption rate of the sensor to be only 83%. In addition, the influence of the external dielectric constant and structural parameters on the sensing characteristics are analyzed to obtain the optimal sensing performance, where the sensitivity of methane is 7.46nm/% and the sensitivity of hydrogen is 1.6nm/%. This conclusion is conducive to the design of active adjustable sensors and has many potential applications in the field of detection.