Scientists develop coating for enhanced thermal imaging through hot windows

“Suppose you want to use thermal imaging to monitor chemical reactions in a high-temperature reaction chamber,” said Gururaj Naik, associate professor of electrical and computer engineering at Rice University and corresponding author of the study. “The problem you have is that the thermal radiation from the window itself floods the camera and blocks the view of objects on the other side.”

One possible solution might involve coating the window with a material that suppresses the emission of hot light toward the camera, but this would also render the window opaque. To solve this problem, researchers developed a coating that relies on engineered asymmetries to filter out thermal noise from thermal windows, doubling the contrast of thermal imaging compared to traditional methods.

At the heart of this breakthrough is the design of nanoscale resonators, which function like tiny tuning forks and capture and amplify electromagnetic waves at specific frequencies. The resonators are made of silicon and arranged in a precise array to precisely control how the window emits and transmits thermal radiation.

“For us, the interesting question is whether it is possible to suppress the thermal radiation emitted by the window towards the camera while maintaining good transmission from the sides of the object to be visualized,” Naik said. “The answer from information theory is ‘no’ for any passive system. However, there is a loophole – the camera actually operates within a limited bandwidth. We took advantage of this loophole and created a coating that suppresses thermal emission Window towards the camera in wideband, but only reduces transmission of imaged objects in narrowband.

This was achieved by designing a metamaterial that consists of two layers of different types of resonators, separated by a spacer layer. The design enables the coating to suppress thermal radiation toward the camera while remaining transparent enough to capture thermal radiation from objects behind the window.

“Our solution to this problem was inspired by quantum mechanics and non-Hermitian optics,” said Ciril Samuel Prasad, an engineering doctoral student at Rice and lead author of the study. “

The result is a revolutionary asymmetric element window capable of producing clear thermal images at temperatures up to 873 K (approximately 600 C).

This breakthrough is of great significance. One immediate application is chemical processing, where monitoring reactions in high-temperature chambers is critical. In addition to industrial uses, this approach could revolutionize hyperspectral thermal imaging by solving the long-standing “narcissus effect,” in which thermal emissions from the camera itself interfere with imaging. The researchers envision applications in energy conservation, radiative cooling and even defense systems where accurate thermal imaging is essential.

“This is a disruptive innovation,” the researchers note. “Not only do we solve a long-standing problem, but we open new doors for imaging in extreme conditions. Using metasurfaces and resonators as design tools could change Many areas beyond thermal imaging, from energy harvesting to advanced sensing technology.

Henry Everitt, a senior scientist at the U.S. Army Research Laboratory and an adjunct professor at Rice University, is also one of the study’s authors.

This research was supported by the U.S. Army Research Office under Cooperative Agreement No. W911NF2120031.