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Temperature Change Hidden From Infrared Cameras By New Coating
January 2, 2020

An ultrathin coating developed by University of Wisconsin-Madison (UW-Madison) engineers upends a ubiquitous physics phenomenon of materials related to thermal radiation: The hotter an object gets, the brighter it glows.

Infrared images show conventional materials (top three rows) appear to an infrared camera as they heat up. Special coatings developed by UW–Madison engineers hide the temperature changes of the objects in the bottom two rows. Image courtesy of Patrick Roney, Alireza Shahsafi and Mikhail Kats.

According to information, the new coating – engineered from samarium nickel oxide, a unique tunable material – employs a bit of temperature trickery.

“This is the first time temperature and thermal light emission have been decoupled in a solid object. We built a coating that ‘breaks’ the relationship between temperature and thermal radiation in a very particular way,” says Mikhail Kats, a UW-Madison professor of electrical and computer engineering. “Essentially, there is a temperature range within which the power of the thermal radiation emitted by our coating stays the same.”

Currently, that temperature range is fairly small, between approximately 105 and 135 degrees Celsius. With further development, however, Prof. Kats says 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.

Prof. Kats, his group members, and their collaborators at UW-Madison, Purdue University, Harvard University, Massachusetts Institute of Technology and Brookhaven National Laboratory published details of the advance recently in the Proceedings of the National Academy of Sciences.

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, says Alireza Shahsafi, a doctoral student in Prof. Kats’ lab and one of the lead authors of the study.

“We can imagine a future where infrared imaging is much more common, negatively impacting personal privacy,” Shahsafi says. “If we could cover the outside of clothing or even a vehicle with a coating of this type, an infrared camera would have a harder time distinguishing what is underneath. View it as an infrared privacy shield. The effect relies on changes in the optical properties of our coating due to a change in temperature. Thus, the thermal radiation of the surface is dramatically changed and can confuse an infrared camera.”

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