Dynamic thermal camouflage via a liquid-crystal-based radiative metasurface

Abstract

Thermal camouflage, which is used to conceal objects in the infrared vision for confrontation with infrared detection in civilian or military applications, has garnered increasing attraction and interest recently. Compared with conductive thermal camouflage, that is to tune heat conduction to achieve equivalent temperature fields, radiative thermal camouflage, based on emissivity engineering, is more promising and shows much superiority in the pursuit of dynamic camouflage technology when resorting to stimuli-responsive materials. In this paper, we demonstrate the emissivity-engineered radiative metasurface to realize dynamic thermal camouflage functionality via a flying laser heat source on the metal-liquid-crystal-metal (MLCM) platform. We employ a rigorous coupled-wave algorithm to calculate the surface emissivity of Au/LC/Au microstructures, where the LC-orientation angle distribution is quantified by minimizing the emitted thermal energy standard deviation throughout the whole plate. Emissivity engineering on the MCLM platform is attributed to multiple magnetic polariton resonance, and agrees well with the equivalent electric circuit analysis. Through this electrical modulation strategy, the moving hot spot in the original temperature field is erased and a uniform temperature field is observed in the infrared camera instead, demonstrating the very good dynamic thermal camouflage functionality. The present MLCM-based radiative metasurface may open avenues for high-resolution emissivity engineering to realize novel thermal functionality and develop new applications for thermal metamaterials and meta-devices.

A Review on Metasurface: From Principle to Smart Metadevices

“…Metasurfaces with LC as the surrounding material was used as all-optical switches [8] and switches of controlling the generation of second harmonics of metasurface [127]. In terms of controlling electromagnetic radiation, the LC-based metasurface was also designed to successfully achieve dynamic thermal camouflage, as shown in Figure 9C, which provides a new development direction for the future thermal metasurface with emissivity engineering [100]. Nanoparticle solutions can also be used a background materials as same as LC.…”

A Review of Tunable Electromagnetic Metamaterials With Anisotropic Liquid Crystals

“…As mentioned in Section 3, LC reorientations would result in a dramatic change in the refractive index of LC, which in turn, would further change the response to electromagnetic waves. In nematic LCs, the crystal is in a rod-shape and the external stimulations such as thermal heating, pressure, and the magnetic and electric field, can control its directional order, resulting in good refractive index tunability [42,59,[74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91]. Therefore, LCs are extensive used as the liquid background of solid metamaterials [51,52,92].…”

“…In addition to the applied voltage, temperature can be also used as an external control parameter [57,76,85,[100][101][102][103][104][105]. Heating of the sample over the liquid crystal transition temperature leads to the phase transition of the liquid crystal between nematic and isotropic, which can be used to realize the tunability of response to electromagnetic waves.…”

Thermal Metamaterial: Fundamental, Application, and Outlook

“…also developed three-dimensional separated thermal illusions through the spatial transformation in the z axis ( Peng and Hu, 2019 ). More recently, thermal camouflage has been promoted with photonic design of surface films ( Qu et al., 2018 ; Li et al., 2020a ; Song et al., 2020 ; Wang et al., 2020a , Liu et al., 2020 ). The radiative wave can be well modulated with surface well-designed structures.…”