Optically Transparent Single-Layer Microwave Metamaterial Absorber

Recent advances in metamaterials have allowed to impart unique properties to flat RF absorbers, including broadband absorption, low thickness (in terms of the longest operating wavelength, lambda(L)), polarization insensitivity, and optical transparency. However, achieving all of these critical characteristics in a single design is a challenging task. Here, we propose and demonstrate an optically transparent and extremely thin metamaterial absorber (with a thickness of 0.079 lambda(L)) made of a single layer of polymethyl methacrylate (PMMA) as the substrate and the indium-tin-oxide films as the ground plane and the patterned layer on top of the PMMA layer. The fabricated prototypes exhibit over 90% absorption between 4.4 GHz and 11.2 GHz and over 95% absorption between 4.8 GHz and 10.6 GHz without any air-gaps. Furthermore, the absorber is insensitive to polarization and provides more than 90% absorption for incident angles up to 60 degrees for transverse magnetic, and 40 degrees for transverse electric polarizations without any compensation layer requirement. Besides RF characterizations, we optically recorded the transmittance in the visible range to be 65% on average for the tested absorbers. The proposed architecture holds great promise for use in stealth air plane canopies due to extended 95% absorption while offering reduced fabrication cost.