Ultrathin, polarization-insensitive multi-band absorbers based on graphene metasurface with THz sensing application

This article presents multi-band plasmonic absorbers based on a graphene array at terahertz frequencies. The absorbers are made of a very simple structure including a graphene disk array printed on the top surface of a dielectric spacer backed by a metallic ground plane. Multi-band performance is achieved with more than 90% absorption in the 1–8 THz frequency range by exciting surface plasmon polaritons of graphene. It is shown that the resonance frequencies of the proposed absorber can be tuned by varying the chemical potential between 0.8–1 eV for a triple-band absorber and 0.7–0.9 eV for a quad-band one, while keeping more than 80% absorption. The results obtained by means of full-wave simulation are verified with the results obtained by the analytical circuit model. The proposed absorbers are polarization-insensitive and provide stable absorption performance for both of the TE and TM polarizations. As an application, we designed a refractive index sensor based on the triple-band absorber. The results verify that the absorption bands are sensitive to the variations of the refractive index of the coating layer.