Engineers Build 3D Thermal Cloak That Hides Complex Objects From Infrared Cameras

Researchers at the University of Illinois Urbana-Champaign have built and tested a three-dimensional thermal cloak that guides heat around an object, making the object appear absent to an infrared camera. The work, done with a collaborator at the Technical University of Denmark, was published in Nature Communications. The team says the device can conceal objects of many shapes regardless of the direction from which heat approaches. Earlier thermal cloaks were limited to two dimensions or worked only when heat traveled in a particular direction. The new design instead directs heat around a hidden object rather than simply blocking it, so an infrared image shows a temperature pattern that makes the object seem to be missing. The research was led by Shelly Zhang, a professor of civil and environmental engineering at Illinois, with postdoctoral researcher Weichen Li and graduate student Yibo Wang, in collaboration with Ole Sigmund of the Technical University of Denmark. "A real thermal cloak should work no matter where the heat comes from," Zhang said. "Our device can hide a complex 3D object in an infinite number of directions while keeping the temperature inside stable and protected." To get there, the researchers returned to the principles of transformation thermotics, a field that studies how heat can be redirected through specially designed materials. They asked what kind of material structure could cover almost all the thermal properties needed for a perfect cloak. Their answer was a new lattice-based material whose structure can be adjusted independently along three directions. That tuning lets them control how efficiently heat passes through different parts of the cloak. According to the researchers, the material achieves a much broader range of thermal conductivities than previous designs, closely approaching the properties predicted to be necessary for ideal cloaking. The team also went beyond computer simulations and built a working device. They used 3D metal printing to make an intricate aluminum lattice that provides pathways for efficient heat conduction. They then used mold casting to fill the remaining spaces with a rubber-like material that conducts heat poorly. Together, the two materials control how heat moves through the structure. For testing, the team placed the device between hot and cold regions, creating a temperature difference that made heat flow through the surrounding environment. An infrared camera recorded the resulting temperature patterns to show whether the cloak redirected heat around the concealed area. The experiments showed that the device guided heat around the hidden region while preserving the surrounding temperature pattern. To the infrared camera, the area looked much as it would if no object were there. Temperatures inside the cloak stayed uniform, shielding the concealed space from the extreme conditions outside. The researchers also tested whether the cloak could handle unusually complicated objects and say they concealed intricate three-dimensional geometries, including detailed shapes resembling human heads. According to the team, earlier experimental thermal cloaks have not shown a comparable combination of geometric complexity and cloaking performance. The researchers see possible uses wherever heat needs precise control. In electronics, the technology could help engineers direct heat away from sensitive components, improve thermal management in microchips, and protect devices operating under demanding conditions. They also point to security and defense, where future versions might help conceal people or equipment from thermal detection systems or shield valuable assets from severe temperatures. These are potential applications rather than demonstrated ones; the tests described involved heat flowing between hot and cold regions and imaging with an infrared camera. "Any field that needs precise control of heat or needs to protect something from being detected thermally could benefit from this work," Zhang said. "But we also see it more broadly: it's about hiding and protecting information that is carried by heat." The current cloak has a clear limitation. It protects an object from heat originating outside the cloak, but it does not hide objects that generate heat themselves. The researchers identify that as a key next goal. Achieving it would require materials that can actively control heat within the concealed region, concentrating, distributing or guiding thermal energy as conditions change. "We've shown that a true 3D omnidirectional thermal cloak is possible," Zhang said. "The next step is to make cloaks that don't just hide and protect, but also actively manipulate heat in useful ways." The research received support from the National Science Foundation, the Villum Foundation, and the Air Force Office of Scientific Research. Zhang is also affiliated with mechanical science and engineering and the National Center for Supercomputing Applications at the University of Illinois Urbana-Champaign.