Transparent and Tunable Radar‐Infrared Bi‐Stealth Metamaterial Based on Water and Metallic Mesh for Optical Window Applications

Abstract In this paper, we present a transparent and tunable radar‐infrared bi‐stealth metamaterial consisting of an infrared shielding layer (IRSL), a radar‐absorbing layer (RAL), a water substrate, and a metal meshed reflective backplane. The IRSL consists of an array of indium tin oxide square patches, reducing infrared emissivity and transmitting microwaves. In the RAL, ultrathin metallic meshes with different periods are integrated into one layer to broaden the microwave absorption bandwidth. Moreover, the water substrate facilitates the tunability of the absorption performance via its fluidity. Experimental measurements and simulations indicate that the fabricated sample can achieve over 90% absorption within a wide frequency range of 3.6–15.8 GHz with a relative bandwidth of 126%. The 90% absorption band can be further switched to 3.6–5.9 GHz and 11.2–13.8 GHz by simply adjusting the water substrate thickness. In addition, a low infrared emissivity of ≈0.37 is achieved in the atmospheric window (8–14 µm), while the measured average optical transmittance reaches 65.5% at 400–800 nm. The main advantage of the proposed metamaterial is its compatibility across visible, infrared, and microwave regions with the simultaneous realization of high optical transparency, reduced infrared emissivity, and broadband and switchable microwave absorption. Given these multiple functionalities and superior performances, the proposed metamaterial has great application potential in aircraft optical windows, glass curtain walls of buildings, counter‐surveillance devices, and wireless communication systems.