Control of absorption properties of ultra-thin metal–insulator–metal metamaterial terahertz absorbers

Abstract

We have systematically investigated the absorption spectra of ultra-thin metal–insulator–metal (MIM) metamaterial absorbers (MMAs) as a function of the insulator thickness, h. Absorption over 90% is obtained when h is optimized. Furthermore, we have found that, when the insulator thickness is increased, the resonance frequency first increases rapidly and, then, shows a gradual red-shift. As a result, the resonance frequency has a bell-shaped dependence on h. To explain the observed dependence, we provide an intuitive, analytical theory and show that the bell-shaped dispersion curve in the MIM MMA structure originates from the transition from the TM0 plasmonic mode to the vertical Fabry–Perot mode.