Scientists develop coating that enhances thermal imaging through hot windows

A team of Rice University scientists has solved a long-standing problem in thermal imaging, making it possible to capture clear images of objects through hot windows. The findings reported in the journal Communications Engineering could benefit imaging applications in a variety of fields, including security, surveillance, industrial research, and diagnostics.

“For example, let’s say you want to use thermal imaging to monitor chemical reactions inside a high-temperature reaction chamber,” said Gururaj Naik, associate professor of electrical and computer engineering at Rice University and corresponding author of the study. ” he said. “The problem faced is that the thermal radiation emitted by the window itself overwhelms the camera and obstructs the view of objects on the other side.”

A possible solution is to coat the window with a material that suppresses thermal light radiation to the camera, but this would make the window opaque. To circumvent this problem, researchers developed a coating that uses engineered asymmetries to eliminate hot window thermal noise, doubling the contrast in thermal images compared to traditional methods. I did.

At the heart of this breakthrough lies the design of nanoscale resonators that act like miniature tuning forks, capturing and amplifying electromagnetic waves within specific frequencies. The resonator is made of silicon and consists of a precise array that allows fine control over how the window emits and transmits thermal radiation.

“An interesting question for us was whether we could suppress heat radiation from the window to the camera while still maintaining good transmission from the sides of the object being visualized,” says Naik. “In information theory, the answer is no for any passive system. But there is a loophole. In reality, cameras operate with finite bandwidth. We took advantage of this loophole to create a coating that suppresses heat radiation from the system. Broadband illuminates the window toward the camera, while narrowband only reduces transmission from the imaged object. ”

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

“Our solution to this problem draws inspiration from quantum mechanics and non-Hermitian optics,” said Cyril Samuel Prasad, a Rice doctoral engineering alumnus and lead author of the study.

The result is an innovative asymmetric metawindow that can capture clear thermal images at temperatures as high as 873 K (approximately 600 °C).

The implications of this breakthrough are significant. One immediate application is chemical processing, where it is important to monitor reactions inside high-temperature chambers. Beyond industrial applications, this approach has the potential to revolutionize hyperspectral thermal imaging by addressing the long-standing “daffodil effect” in which thermal radiation from the camera itself impedes 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 said. “We have not only solved a long-standing problem, but also opened a new door in imaging in extreme conditions. By using metasurfaces and resonators as design tools, we have developed technologies from energy harvesting to advanced sensing. “Many fields beyond thermal imaging have the potential to be transformed.”

Henry Everitt, a senior research scientist at the U.S. Army Research Institute and an adjunct faculty member at Rice University, is also an author on the study.