Total resonant terahertz absorption enabled by large-scale adjustable admittance inverse matching in a metal groove with graphene

Abstract We propose a tunable terahertz (THz) perfect absorber based on a metal groove with a graphene-loaded dielectric resonator, and theoretically study its basic properties. The proposed absorber allows switching between the regimes of perfect absorption at the Fabry–Pérot resonance excited near the cutoff frequency of the metal groove and almost total reflection away from the resonance by changing the Fermi energy in the graphene. For this purpose, we propose a ‘bottom–up’ approach, which is based on tuning the admittance of the input line (the metal groove in our case) instead of the structure admittance in order to reach the perfect admittance-matching condition. We demonstrate that this effect can be realized at arbitrarily selected frequencies in the entire THz range due to the dispersion of incoming waves in the metal groove, which ensures the large-scale tunability of its characteristic admittance. As a result, total absorption can be realized in the Fabry–Pérot resonance even in a simple graphene-loaded dielectric cavity for any admittance of the graphene layer, which is advantageous compared to the majority of existing THz absorbers with more complicated designs.