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In this study, a tunable and optically transparent water-based wideband metamaterial absorber (MMA) is proposed and verified. By adjusting the thickness of the water layer, the conversion of the absorber absorption band from 7.4-22.4 GHz to 23.1-35.5 GHz can be achieved, which demonstrates the flexibility of MMA. Indium tin oxide (ITO) as the resonant and reflective layers of the material structure. Optically transparent polymethyl methacrylate (PMMA) is used as a medium container to encapsulate the water. Furthermore, the suggested MMA is polarization insensitive and has broad incident angle stability. Experiments verify the excellent properties of the proposed MMA. As a result, the suggested MMA has various applications in military and medical equipment optical windows.

The rapid development of surveillance technology has driven the research of multispectral stealth. Demand for infrared and microwave radar compatible stealth is becoming increasingly urgent in military applications. Herein, a versatile metamaterial absorber is designed and fabricated to simultaneously achieve ultra-broadband radar scattering reduction, low infrared emission, and high optical transparency. The designed structure consists of an infrared stealth layer, radar absorption layers, and backing ground. The infrared stealth layer employs specifically indium tin oxide (ITO) square patches, while the radar absorption layers can be obtained by stacking different size ITO patterned films of the same structure with high surface resistances, realizing broadband microwave stealth performance in the 1.98 to 18.6 GHz frequency range with an incident angle of 45º. The broad radar stealth and low infrared emissivity of 0.283 are consistent with the simulations and calculations. Furthermore, the designed structure exhibits characteristics such as polarization insensitivity, wide incident angles, optical transparency, and flexibility, allowing for a wide range of applications in various environments.

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