We present a simple design of a multiband tunable perfect metamaterial absorber (MMA) for refractive index sensing application. The MMA consists of a two-dimensional periodic array of circular discs made of VO \({}_{2}\) separated from a continuous metallic silver film by a continuous dielectric film having constant refractive index 1.65. The optical responses of the proposed metamaterial structure at mid-infrared frequency range are investigated by using the Comsol Multiphysics software based finite element method. Our proposed model demonstrates three distinct absorption peaks in the wavelength range of \(1.5~\mu \text {m}\) to \(3~\mu \text {m}\) when VO \({}_2\) is in its dielectric phase. However, upon transition to the metallic phase, the proposed model exhibits two distinct absorption peaks with efficiencies greater than \(90\%\) over the wavelength range of 1.5–2.5 and the third peak of efficiency greater than 80 \(\%\) . We numerically simulated the electromagnetic field distribution at resonant wavelengths for both metallic and insulating phases of the top VO \({}_{2}\) circular disc in order to understand the underlying physics behind such unit absorption. The study reveals that the absorption spectra are enhanced due to localized and vertical cavity mode resonances for the dielectric phase of VO \({}_{2}\) and for the metalic phase of VO \({}_{2}\) the enhanced absorption spectra are due to the localized and fundamental mode of electromagnetic dipolar resonance. The tunability nature of the absorption spectra are studied in detail by varying various geometrical parameters of the proposed MMA structure like the thickness of the circular VO \({}_{2}\) disc, the thickness of the dielectric spacer layer, and also the launching angle. We discuss the sensing applicability of our proposed MMA structure at mid-infrared wavelength band by changing the refractive index of the ambient surrounding medium for both the metallic and dielectric phase of top VO \({}_2\) .
