Theoretical and Experimental Demonstrations of a Dual-Band Metamaterial Absorber at Mid-Infrared

We present the design, fabrication, and physical interpretation of an infrared dual-band metamaterial absorber. The unit cell of the metamaterial absorber consists of a cross resonator ringed by four split-ring resonators spaced a distance above a gold ground plane with a dielectric layer of SiO₂. The absorber shows two absorption peaks of 90.3% and 88.4% at 4.17 μm and 4.86 μm, respectively. The multireflection interference theory is applied to explain the absorption mechanism with the gold ground plane described by Drude model, and the theoretical calculation agrees well with the simulations and experiments. In addition, the designed absorber is insensitive to incident angle and polarization direction in a broad range, which are highly favorable features in practical applications.