Thermal stealth and camouflage have been intensively studied for blending objects with their surroundings against remote thermal image detection. Adaptive control of infrared emissivity has been explored extensively as a promising way of thermal stealth, but it still requires an additional feedback control. Passive modulation of emissivity, however, has been remained as a great challenge which requires a precise engineering of emissivity over wide temperature range. Here, we report a drastic improvement of passive camouflage thin films capable of concealing thermal objects at near room temperature without any feedback control, which consists of a vanadium dioxide (VO2) layer with gradient tungsten (W) concentration. The gradient W-doping widens the metal-insulator transition width, accomplishing self-adaptive thermal stealth with a smooth change of emissivity. Our simple approach, applicable to other similar thermal camouflage materials for improving their passive cloaking, will find wide applications, such as passive thermal camouflage, urban energy-saving smart windows, and improved infrared sensors.
@article{arxiv.2105.06063,
title = {Enhanced passive thermal stealth properties of VO$_2$ thin films via gradient W doping},
author = {Hyuk Jin Kim and Young Hwan Choi and Dong Kyu Lee and In Hak Lee and Byoung Ki Choi and Soo-Hyun Phark and Young Jun Chang},
journal= {arXiv preprint arXiv:2105.06063},
year = {2021}
}