Color-thermal multispectral camouflage with VO2-based dynamic regulator

Camouflage technologies rely on effective integration with the surrounding environment, which can significantly reduce the detectability of targets and thereby enhance their concealment. With the continuous advancement of detection technologies, conventional camouflage approaches are facing new challenges, particularly when targets operate in dynamic environments and under complex conditions. Among various camouflage strategies, color camouflage and thermal camouflage are of particular significance. Therefore, the development of high-performance, dynamically tunable camouflage technologies holds substantial research value.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Xun Cao from State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai institute of Ceramics, Chinese Academy of Sciences, China, and co-workers have developed a multispectral dynamic regulator based on vanadium dioxide (VO₂) for tunable control in visible and mid-infrared bands. Leveraging the structural design of Bragg reflector and negative emissivity tunability layer, the VO₂-based device ensures wide color gamut variation while simultaneously achieving negative emissivity tunability (Δε_{8–14 μm}=-0.58), which experimentally achieves dynamic color-thermal camouflage among VO₂-based devices. To go a step further, they advance the device featuring long-term cycling stability to achieve thermal-electric dual-mode response and flexibility for a series real-world camouflage performance evaluation. They have also demonstrated the digital camouflage based on multispectral dynamic regulator through Neighboring Color Block Camouflage Algorithm, highlighting its potential for practical implementation in different camouflage scenarios.

 

The multispectral dynamic regulator is composed of two main functional components: the top thermochromic Bragg reflector, and the bottom negative emissivity tunability layer. These multilayer films, consisting of thermochromic VO₂ and visible-infrared transparent dielectric hafnium dioxide (HfO₂), are alternately grown on high emissivity quartz with magnetron sputtering method. The significant variation in the optical constants of VO₂ across a broadband will profoundly impact the overall optical performance of the device. In the visible band, the top Bragg reflector allows the device to dynamically modulate its reflective color under different temperature. Furthermore, by adjusting the film thicknesses, the central wavelength for reflection can be regulated correspondingly, providing a diverse range of reflective color combinations to align with various scenarios. As for the mid-infrared band, emissivity is modulated by the bottom VO₂ under different phases. These scientists summarize the operational principle of their device:

 

“The key point is that, on one hand, the thicker VO₂ layer at the bottom does not interfere with the top layer's reflection modulation due to the high visible absorption, while on the other hand, the infrared-transparent HfO₂ ensures that the emissivity tunability of the bottom layer is not affected by the top structure, thus achieving functionally independent control of visible and mid-infrared bands.”

 

“As a result, the target can seamlessly blend into the background under visible and infrared detection, regardless of whether it is at a low or high temperature. Compared with static camouflage technology, multispectral dynamic regulator will not only enhance dynamic camouflage performance across diverse environments, but also mitigates interference from additional heat sources.” they added.

 

“With the advancement of multispectral detection technology and the increasing complexity of camouflage scenario requirements, the demand for multispectral dynamic camouflage technology is growing increasingly urgent. The integration of advanced camouflage technologies with materials science, optoelectronic detection, computational algorithms, and physics will further accelerate interdisciplinary interaction and collaborative development. We expect that the designed device can not only advance the progress of multispectral dynamic camouflage, but also expand to information anti-counterfeiting, flexible electronics and thermal management.”the scientists forecast.

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