This coating has broad potential applications in fields such as security, surveillance, industrial diagnostics and research.
A team of researchers from Rice University (Houston, Texas, United States) has developed an innovative coating that overcomes a long-standing challenge in thermal imaging, enabling clear visualization of objects through hot windows.
Traditional attempts to solve this problem involve coating windows with materials that suppress thermal light emissions toward the camera. However, this approach typically makes the window opaque, obstructing visibility. To overcome this limitation, the Rice researchers developed a novel coating that uses engineered asymmetry to filter out thermal noise while maintaining transparency. In addition, their solution effectively doubles the contrast of thermal imaging compared to conventional methods.
“Say you want to use thermal imaging to monitor chemical reactions in a high-temperature reactor chamber. The problem you’d be facing is that the thermal radiation emitted by the window itself overwhelms the camera, obscuring the view of objects on the other side,” has stated Gururaj Naik, an associate professor of electrical and computer engineering at Rice and corresponding author on the study.
At the heart of this innovation is the design of nanoscale resonators—structures that function like tiny tuning forks, trapping and enhancing electromagnetic waves at specific frequencies. Made from silicon, these resonators are precisely arranged in arrays, allowing controlled emission and transmission of thermal radiation.
The coating is achieved using a metamaterial composed of two distinct layers of resonators separated by a spacer layer. This design suppresses thermal emissions directed toward the camera while permitting thermal radiation from objects behind the window to pass through.
“The intriguing question for us was whether it would be possible to suppress the window’s thermal emission toward the camera while maintaining good transmission from the side of the object to be visualized. Information theory dictates a no for an answer in any passive system. However, there is a loophole ⎯ in actuality, the camera operates in a finite bandwidth. We took advantage of this loophole and created a coating that suppresses thermal emission from the window toward the camera in a broad band but only diminishes transmission from the imaged object in a narrow band,” has added Gururaj Naik.
The result is an advanced asymmetric meta-window capable of delivering clear thermal images at temperatures up to 600° C. The implications are far-reaching. For instance, in chemical processing, the technology allows for precise monitoring of reactions occurring within high-temperature chambers. Beyond industrial applications, this approach could revolutionise hyperspectral thermal imaging by solving the persistent Narcissus effect, where the camera’s own thermal emissions interfere with imaging quality.
“Our solution to the problem takes inspiration from quantum mechanics and non-Hermitian optics. This is a disruptive innovation. We’ve not only solved a long-standing problem but opened new doors for imaging in extreme conditions. The use of meta-surfaces and resonators as design tools will likely transform many fields beyond thermal imaging from energy harvesting to advanced sensing technologies,” has concluded Ciril Samuel Prasad, a Rice doctoral engineering alum and first author on the study.
The researchers also anticipate applications in energy conservation, radiative cooling and defence systems, where accurate thermal imaging is crucial. This breakthrough represents a significant leap in thermal imaging capabilities, paving the way for improved performance in extreme environments.