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We present a comprehensive investigation of a continuously tunable metamaterial perfect absorber operating at terahertz frequencies. In particular, we investigate a three-layer absorber structure consisting of a layer of split ring resonators and a metallic ground plane, with a central layer consisting of a mechanically tunable air-spaced layer. The absorber was characterized using terahertz time-domain spectroscopy in reflection (at normal incidence) as a function of spacer thickness from 0 to 1000 μm. Our experimental measurements reveal the detailed evolution of the absorption bands as a function of spacing, in excellent agreement with analysis using interference theory and simulation. Our Fabry-Perot-like structure provides an avenue for achieving massive tunability in metamaterial absorber devices.

We present a three-dimensional terahertz metamaterial perfect absorber (MPA) that exhibits a high quality factor and is polarization insensitive. The unit cell is composed of two orthogonally oriented copper stand-up split ring resonators deposited on a copper ground plane with capacitive gaps in free space away from the substrate. Near unity (99.6%) absorption at ∼1.65 THz is experimentally obtained in excellent agreement with simulation results. The quality factor is ∼37, which is quite large for a terahertz MPA because of reduced material losses in the all-metal structure. According to simulation results, the MPA is insensitive to the polarization of the incident wave, and more than 90% absorption can be achieved for angles of incidence up to 60° for both TE and TM polarized incident THz waves.