Within the air, IR light – within a specific range called mid-wave infrared – scatters much less compared to other visible or IR light waves. Infrared cameras can also see more effectively in the dark, when there is no visible light. However, currently the deployment of infrared cameras is limited by their heavy cost and scarcity of effective materials. This is where materials, which possess unique optical properties in the infrared and can be scalable, might make a difference in providing better object identification in several technologies including autonomous vehicles.
A new material developed by scientists at the USC Viterbi School of Engineering (USC) and the University of Wisconsin along with researchers from Air Force Research Laboratories, University of Missouri, and J.A. Woollam, might show promise for IR detection applications in autonomous vehicles, emergency services and even manufacturing.
The research group of Jayakanth Ravichandran, an assistant professor of materials sciences at USC has been studying a new class of materials called chalcogenide perovskites. Among these materials is Barium titanium sulphide (BTS), a material rediscovered and prepared in large crystal form by Shanyuan Niu, a doctoral candidate in the USC’s Department of Chemical Engineering and Materials Science. Prof Ravichandran's research group collaborated with the research groups of Mikhail Kats, an assistant professor of electrical and computer engineering at University of Wisconsin-Madison and Han Wang, an assistant professor of electrical engineering and electrophysics in USC's Department of Electrical Engineering to study how IR light interacts with this material. These researchers discovered that this material interacted differently with light in two different directions.
This direction dependent interaction with light is characterised by an optical property called birefringence. In simple terms, birefringence can be viewed as light moving at different speeds in two directions in a material. BTS has the ability to block or slow down light depending on the direction in which it travels in the material. The researchers maintain that their material, barium titanium sulphide, has the highest birefringence among known crystals.
Prof Kats said: “The birefringence is larger than that of any known solid material, and it has low losses across the important long-wave infrared spectrum.”
How BTS could improve IR vision:
The BTS material can be used to construct a sensor to filter out certain polarisations of light to achieve better contrast of the image. It could also help filter light coming from different directions to enable sensing of a remote object’s features. This could be particularly important for improving IR vision used in autonomous vehicles, which need to see the entire landscape around them even in low visibility conditions.
Niu said: “The hope is that in the future, a BTS-enhanced sensor in a car would function as retinas do to the human body.”
The authors believe these IR-responsive materials can extend human perception. Beyond autonomous vehicles, there are other possible heat sensing or temperature measurement applications. One application could be in the creation of imaging tools used by firefighters to generate an instant temperature map outside a burning building to assess where a fire is spreading and where emergency responders need to rescue trapped individuals.
At present, the cost of infrared equipment makes it too expensive for all fire stations to have such equipment. BTS, which is made of elements readily abundant in earth crust, could make IR equipment more affordable and effective. In addition, such materials are safer for the user and the environment, as well as easier to dispose of than the materials that are used now, which contain hazardous elements such as mercury and cadmium.
These materials could also be useful in devices that sense harmful molecules, gases, even biological systems. The applications range from heat sensing, pollution monitoring to medicine.
The researchers hope that more research in this area will make several of these technologies a reality soon.
