Tunable quintet ultra-narrowband metamaterial absorber based on Pi-inverted-Pi structures

In this article, a metamaterial multi-band perfect absorber with a Pi-inverted-Pi resonator is designed and investigated. It is observed that the meta-surface with a typical metal–insulator-metal structure showed nearly perfect absorption in almost five narrow bands with the lowest 93.6% and the highest 99.7% absorption level, according to the full-wave simulation results. The tunability of the Pi-inverted-Pi resonator has been examined based on the geometrical parameters. The origin of the five resonance bands has been analyzed based on the electric field and charge distributions occurring at the metal–dielectric interface. These resonance peaks are located at 1817.52 nm, 1968.38 nm, 2721.31 nm, 3765.6 nm, and 5740.63 nm wavelengths. The polarization dependence of the structure is investigated under TE and TM light, and our findings reveal that the Pi-inverted-Pi structure is partially polarization-dependent, which is a beneficial property for optical filtering. Compared to similar multi-band absorbers in the literature to the best of our knowledge, our proposed system offers a narrow band with high Q-factors of 118.7, 53, 32, 33, and 32 at each resonance wavelength. Therefore, our proposed design can be used in optical filters, Raman spectroscopy, bio-sensing, and many other applications, especially for the mid-infrared region’s spectroscopic sensing and filtering applications.