Adaptive Electrochromic Camouflage for Thermal and Visual Adaptation in Terrestrial Environments

The demand for camouflage is increasing because of surveillance technologies such as UAVs and commercial satellites. Traditional camouflage methods fall short in the face of advanced detection technologies, including multispectral sensing, high-resolution imaging, and AI inspection. Designing multi-band camouflage capable of operating across different spectral bands, influenced by electromagnetic material properties, while achieving real-time adaptability to diverse environments presents a significant and even greater challenge.<br/><br/>Recent studies have extensively focused on enhancing camouflage performance across multiple spectral bands and adapting to diverse backgrounds. Techniques such as photonics crystals, metasurfaces, and nested structures mimic environmental radiative signatures, while electrochromism, phase-change materials, and physical transformation have explored switchable camouflage functions. This study presents an electrically controllable dual-band camouflage thin-film system for visual and thermal adaptation in various environments.<br/><br/>To effectively design camouflage for diverse environments, an investigation into the radiative properties of terrestrial surfaces was conducted. Despite the variation in surface colors, there exists a commonality in their infrared (IR) emissions. A dual-band camouflage strategy was formulated based on these shared IR emissivity characteristics. We studied unique camouflage requirements for well-illuminated and low-light environments. An essential tactic involves radiant cooling to modify color and solar range emissions.<br/><br/>The camouflage device design is composed of a thermally emissive layer and a color-changing layer for spectral-selective switching. The top layer enables solar transparency while the bottom adjusts colors. The device changes its color and solar absorption by layering electrochromic materials on emissive substrates and adjusting voltage (0 V = light colors / 2 V = near black). Tests in simulated environments demonstrate the device's adaptability to various backgrounds, depending on voltage and substrate type (rigid = 0 V / 2 V, flexible = 0 V / 2 V).<br/><br/>Outdoor experiments evaluated active double-band camouflage devices in a variety of virtual environments. Rigid samples were visually thermally camouflaged to environments of snow for 0 V and deep blue silt for 2 V. Flexible samples showed excellent visual camouflage performance to conditions of bright sand for 0 V and black soil for 2 V. Despite the windy conditions affecting the thermal vision test, the device matched the thermal signature in the target environment. The camouflage device, designed with high emissions, showed a cooling effect, and outperformed the non-cooling reference sample.<br/><br/>In conclusion, spectral designs for visual and thermal camouflage in two terrestrial environments were developed and assessed using electrochromic devices. The design enables seamless transitions between environments by adjusting visible spectral emittance. A practical camouflage solution was achieved without the need for laborious optimization and trial-and-error methods. Furthermore, the devices offer radiative cooling, flexibility, and compatibility with existing camouflage schemes, due to their large design degrees of freedom, thus benefiting security and defense applications.