Engineers Take a Peek Below Materials' Surfaces with Novel Depth Thermography Technique

Engineers at the University of Wisconsin-Madison have developed a technique for overcoming one of the biggest flaws of thermal cameras and traditional thermometers: their inability to see through the surface of an object to read the temperature inside.

Thermal photography is an incredibly useful tool for everything from electrical engineering to healthcare, turning invisible infrared radiation into a colorful glimpse of surface temperatures. The key there, however, is "surface:" Like a contact thermometer, thermal cameras are unable to see below the surface, and depending on what that surface is made of the recorded and actual material temperatures can be considerably different.

To address this, a team of engineers has developed a technique for creating a three-dimensional thermal model — peering below the surface and into objects' inner materials for an accurate view of actual temperatures.

"We can measure the spectrum of thermal radiation emitted from the object and use a sophisticated algorithm to infer the temperature not just on the surface, but also underneath the surface, tens to hundreds of microns in," explains Mikhail Kats, associate professor of electrical and computer engineering at UW-Madison. "We’re able to do that precisely and accurately, at least in some instances."

There's a catch, of course: The team's depth thermography technique relies on the use of materials which are semi-transparent to infrared radiation, though even that restriction opens the method up for exploitation in a range of fields. Kats explains potential uses including analysis of semiconductor devices like microprocessors and volumetric mapping of high-temperature gases and liquids.

"For example, we anticipate relevance to molten-salt nuclear reactors, where you want to know what’s going on in terms of temperature of the salt throughout the volume," Kats says of the latter potential. "You want to do it without sticking in temperature probes that may not survive at 700 degrees Celsius for very long."

The team's work has been published in the journal ACS Photonics under open-access terms.