Coating Hides Temperature Change from Infrared Cameras

University of Wisconsin, Madison, WI

Infrared images show how conventional materials (top three rows) appear to an infrared camera as they heat up. The new coatings hide the temperature changes of the objects in the bottom two rows. (Image: Patrick Roney, Alireza Shahsafi, and Mikhail Kats)

An ultrathin coating was developed that contradicts a physics phenomenon of materials related to thermal radiation: The hotter an object gets, the brighter it glows. The new coating is engineered from samarium nickel oxide, a unique tunable material. The coating “breaks” the relationship between temperature and thermal radiation; essentially, there is a temperature range within which the power of the thermal radiation emitted by the coating stays the same.

Currently, that temperature range is fairly small, between approximately 105 °C and 135 °C. With further development, the coating could have applications in heat transfer, camouflage, and as infrared cameras become widely available to consumers, even in clothing to protect people’s personal privacy.

The coating itself emits a fixed amount of thermal radiation regardless of its temperature. That’s because its emissivity — the degree to which a given material will emit light at a given temperature — actually goes down with temperature and cancels out its intrinsic radiation. The effect relies on changes in the optical properties of the coating due to a change in temperature. Thus, the thermal radiation of the surface is dramatically changed and can confuse an infrared camera.

In the lab, researchers suspended two samples — a coated piece of sapphire and a reference piece with no coating — from a heater so that part of each sample was touching the heater and the rest was suspended in much cooler air. When they viewed each sample with an infrared camera, they saw a distinct temperature gradient on the reference sapphire from deep blue to pink, red, orange, and almost white, while the coated sapphire’s thermal image remained largely uniform.

For more information, contact Mikhail Kats at This email address is being protected from spambots. You need JavaScript enabled to view it.; 608-890-3984.