Enhanced passive thermal stealth properties of VO$_2$ thin films via gradient W doping

TL;DR

This paper presents a novel VO2 thin film with gradient W doping that passively adapts its emissivity over a wide temperature range, enabling effective thermal camouflage without feedback control.

Contribution

It introduces a gradient W-doping technique in VO2 films to passively enhance thermal stealth by broadening the metal-insulator transition.

Findings

W-doping widens the transition width, improving passive thermal camouflage.

The film effectively conceals thermal objects at near room temperature.

The approach is simple and applicable to other thermal camouflage materials.

Abstract

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.