Performance enhancement due to a top dielectric coating on a metamaterial perfect absorber

A tri-layer metamaterial structure with enhanced absorption is demonstrated at infrared wavelengths by coating the top surface of the metamaterial absorber with an additional thin layer of dielectric material. The metamaterial absorber, which consists of a micrometer-sized metallic circular patch separated from a metal ground plane by a dielectric spacer layer, when coated with a supplementary protective dielectric layer on the top, shows a spectral red shift of the peak absorption along with a change in the absorption amplitude. The increase or decrease in absorption arises basically from an interference phenomenon of light reflected from the surface of the protective dielectric and the surface of metamaterial structures, and is highly dependent on the thickness of the top dielectric layer. The protective dielectric coatings provide an alternative way to modify and optimize the absorption in a metamaterial absorber along with a robustness that protects metamaterial structures from environmental and mechanical degradation.