In recent years,metamaterials have attracted great attention in stealth technology. As a special two-dimensional metamaterial,hypersurface is more suitable for the design of infrared radar compatible stealth structures. Based on optically transparent materials Indium Tin Oxide (ITO), Polyethylene Terephthalate (PET) and Polymethyl Methacrylate (PMMA), an optically transparent infrared radar compatible stealth composite metasurface is realized by using the idea of integrated design of infrared low emission layer and radar absorbing layer. The structure consists of three parts:functional layer,dielectric layer,and reflective back plate,with a total thickness of only 1.17 mm. By etching the ITO pattern on the surface of the functional layer and optimizing the pattern size of the pattern,the broadband absorption higher than 90% in the frequency range of 15.9 similar to 35.1 GHz in the microwave band is realized. At the same time,the infrared emissivity is reduced by increasing the ITO duty cycle on the surface of the functional layer,and the infrared emissivity on the surface of the structure is controlled at 0.25. Based on the analysis of the surface current of the material,the mechanism of super surface absorbing wave is expounded,and the influence of different patches on the absorbing wave ability is analyzed. Through the analysis of surface current,it is found that almost only the small square patch in the middle and four large square patches around form the resonant structure,while the four rectangular patches and the peripheral square patches make little contribution to the resonant consumption. When the middle rectangular patch does not exist,the bandwidth absorbed by 90% of the high frequency part can be increased by nearly 5 GHz,but it also means that the proportion of ITO on the surface of the structure is reduced,which affects the infrared emissivity of the whole structure. Through simulation experiments,the changes of the absorbing capacity of the designed structure at different incident angles are discussed. For TE mode, the structure can maintain high absorptivity when the incident angle is less than 30 degrees. With the further increase of the angle,the absorptivity of the low- frequency part decreases more. For TM mode,the absorptivity of the structure is only about 0.8 when the incident angle is small. With the increase of the incident angle to 35 degrees,the structure can maintain 90% absorptivity in the range of 20.1 similar to 35.0 GHz. It shows that the absorbing ability of the structure at large incident angle in TM mode is stronger than that in TE mode. In order to further verify the simulation results,the conductive ITO film deposited on the optically transparent PET substrate was etched into the designed structure by laser etching technology,and the experimental sample was processed,the sample size was 360 mm x 360 mm. The microwave absorption capacity,infrared emissivity and visible light transmittance of the sample were measured respectively. The microwave absorption performance is tested in the microwave darkroom. The measurement system is composed of Agilent N5224a network analyzer and three pairs of broadband horn antennas. During the measurement,the metal base plate with the same size is selected for normalization,and then the reflectivity is measured. After calculation,the absorption curve is obtained. Considering the square resistance and size error of ITO in sample processing, it is considered that the experimental results are basically consistent with the simulation results. The optical transparency performance is measured by ultraviolet visible spectrophotometer (model:uv-3600 plus). After calculation,the average visible light transmittance of the overall structure is about 0.704. The results effectively show that the designed integrated infrared radar compatible stealth composite hypersurface has good optical transparency performance in the visible band. For the infrared emissivity of the designed structure,Tss-5x infrared emissivity tester(spectral response range:2 similar to 22 mu m) and FTIR spectrometer are used to measure the emissivity of the sample. ITO film of 6.0 Omega/sq,pet substrate and material samples etched with ITO pattern are measured respectively. In order to ensure the effectiveness of the measured data,each material is measured at five different positions,and the obtained infrared emissivity is 0.246, which is very close to the average infrared emissivity of the designed material sample obtained by direct measurement of 0.248. The infrared emissivity of the sample with the designed structure in the range of 3.0 similar to 14.0 mu m is measured by FTIR spectrometer,which is about 0.25,which is close to the theoretical calculation value and the measurement value obtained by Tss-5x infrared emissivity tester. It can be considered that the designed structure has better infrared stealth ability. The structure has thin thickness, good broadband radar absorption performance,low infrared emissivity and visible light transparency.
