Optically transparent coding metasurface with simultaneously low infrared emissivity and microwave scattering reduction

In this paper, an optically transparent coding metasurface structure based on indium tin oxide (ITO) thin films with simultaneously low infrared (IR) emissivity and microwave scattering reduction is proposed. To this end, two ITO coding elements which can reflect 0° and 180° phase responses are firstly designed. Based on these two elements, four coding sequences with different scattering patterns are designed. Three of them can realize anomalous reflections and the fourth can realize random diffusion of normal incident electromagnetic (EM) waves. A prototype of the random diffusion coding metasurface was fabricated and measured. The experimental results show that for normal incident EM waves, at least 10dB backward scattering reduction from 3.8GHz to 6.8GHz can be achieved, and the structure is polarization insensitive. The averaged transmittance of visible light through the coding metasurface reaches up to 72.2%. In addition, due to the high occupation ratio of ITO on the outside of the coding metasurface, a low IR emissivity of about 0.275 is obtained. Good consistency between the experiment and simulation results convincingly verifies the coding metasurface. Due to its multispectral compatibility, the proposed coding metasurface may find potential applications in multi-spectral stealth, camouflage, etc.