Exceptional adaptable MWIR thermal emission for ordinary objects covered with thin VO2 film
Monotonous thermal radiation emitted from an ordinary object can be brought into a dynamic and versatile form that can be shaped according to the application area with the ingenious design of the surface coatings. Building the coatings with phase change materials provides exceptional and surprising properties in terms of tunability, adaptability and multifunctionality. In this paper, we investigate the thermal radiation properties in the MWIR band through comprehensive thermographic measurements and theoretical methods while a thin (similar to 90 nm thick) vanadium dioxide (VO2) layer on the sapphire substrate (VO2 thin film) is placed on different ordinary objects under heating/cooling conditions. It is indicated that the emission of the metal object (low emittance) can be boosted and the emission of the blackbody-like object (high emittance) can be suppressed at the relevant temperatures. The thermal emission of the objects covered with thin VO2 film at high temperatures (>75 degrees C) is determined by only the VO2 thin film, since the VO2 layer is completely metallized and the MWIR radiation of the underlying object is masked. When the actual temperature of the object behaving like a blackbody rises up to 95 degrees C, the temperature detected in the MWIR thermal camera is reduced by more than 20% to approx. 75 degrees C due to the VO2 thin film on this object, providing thermal camouflage. It is experimentally and theoretically revealed that the underlying physical mechanism on these strange results is associated with the drastic change in the infrared optical parameters of the VO2 as a result of the applied temperature. (C) 2020 Elsevier Ltd. All rights reserved.