Quantum material ‘camouflage’ hides objects from infrared cameras

Technology News | December 20, 2019

By Rich Pell

The quantum material in this study tricks an infrared camera by decoupling an object’s temperature from its thermal light radiation – which is counterintuitive based on what is known about how materials behave according to fundamental physics laws – allowing information about an object’s temperature to be hidden from an infrared camera. The effect, say the researchers, works for a range of temperatures that one day could include humans and vehicles, presenting a future asset to stealth technologies.

Researchers have previously developed other materials for hiding objects from cameras such as graphene and black silicon that toy with electromagnetic radiation, but the way the quantum material studied here – samarium nickel oxide – tricks an infrared camera is unique. While the discovery does not violate any laws of physics, say the researchers, it suggests that these laws might be more flexible than conventionally thought.

Earlier this year, Purdue researchers co-discovered that the material also has the counterintuitive ability to be a good insulator of electrical current in low-oxygen environments, rather than an unstable conductor, when oxygen is removed from its molecular structure. In addition, say the researchers, samarium nickel oxide is one of a few materials that can switch from an insulating phase to a conducting phase at high temperatures, which led University of Wisconsin-Madison researcher Mikhail Kats to suspect that materials with this property might be capable of decoupling temperature and thermal radiation.

“There is a promise of engineering thermal radiation to control heat transfer and make it either easier or harder to identify and probe objects via infrared imaging,” says Kats, an associate professor of electrical and computer engineering.

Purdue researchers created films of samarium nickel oxide on sapphire substrates to be compared with reference materials. Kats’ group then measured spectroscopic emission and captured infrared images of each material as it was heated and cooled. Unlike other materials, samarium nickel oxide barely appeared hotter when it was heated up and maintained this effect between 105 and 135°C.

“Typically, when you heat or cool a material, the electrical resistance changes slowly,” says Shriram Ramanathan, a professor of materials engineering at Purdue. “But for samarium nickel oxide, resistance changes in an unconventional manner from an insulating to a conducting state, which keeps its thermal light emission properties nearly the same for a certain temperature range.”

Because thermal light emission doesn’t change when temperature changes, that means the two are uncoupled over a 30-degree range. As a result, say the researchers, this study paves the way for not only concealing information from infrared cameras, but also for making new types of optics and even improving infrared cameras themselves.

Next, say the researchers, they are looking forward to exploring this material and related nickel oxides for infrared camera components such as tunable filters, optical limiters that protect sensors, and new sensitive light detectors. For more, see “Temperature-independent thermal radiation.”