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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.

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Thanks to the conductive thermal metamaterials, novel functionalities like thermal cloak, camouflage and illusion have been achieved, but conductive metamaterials can only control the in-plane heat conduction. The radiative thermal metamaterials can control the out-of-plane thermal emission, which are more promising and applicable but have not been studied as comprehensively as the conductive counterparts. In this paper, we theoretically investigate the surface emissivity of metal/insulator/metal (MIM, i.e., Au/Ge/Au here) microstructures, by the rigorous coupled-wave algorithm, and utilize the excitation of the magnetic polaritons to realize thermal camouflage through designing the grating width distribution by minimizing the temperature standard deviation of the overall plate. Through this strategy, the hot spot in the original temperature field is removed and a uniform temperature field is observed in the infrared camera instead, demonstrating the thermal camouflage functionality. Furthermore, thermal illusion and thermal messaging functionalities are also demonstrated by resorting to using such an emissivity-structured radiative metasurface. The present MIM-based radiative metasurface may open avenues for developing novel thermal functionalities via thermal metasurface and metamaterials.

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Near-field radiative heat transfer (NFRHT) governed by evanescent waves, provides a platform to thoroughly understand the transport behavior of nonradiative photons, and also has great potential in high-efficiency energy harvesting and thermal management at the nanoscale. It is more usual in nature that objects participate in heat transfer process in many-body form rather than the frequently-considered two-body scenarios, and the inborn mutual interactions among objects are important to be understood and utilized for practical applications. The last decade has witnessed considerable achievements on many-body NFRHT, ranging from the establishment of different calculation methods to various unprecedented heat transport phenomena that are distinct from two-body systems. In this invited review, we introduce concisely the basic physics of NFRHT, lay out various theoretical methods to deal with many-body NFRHT, and highlight unique functionalities realized in many-body systems and the resulting applications. At last, the key challenges and opportunities of many-body NFRHT in terms of fundamental physics, experimental validations, and potential applications are outlined and discussed.

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