Researchers at the University of Illinois Urbana-Champaign have designed and built the first three-dimensional device that can render objects invisible to heat, a breakthrough published in Nature Communications that could transform thermal management in electronics, defense, and security.

Unlike previous thermal cloaks that only worked in two dimensions or from a single direction, this new device operates from essentially any angle. Rather than simply blocking heat, it guides thermal energy around an object so that, to an infrared camera, it appears as if nothing is there.

"A real thermal cloak should work no matter where the heat comes from," said Shelly Zhang, professor of civil and environmental engineering at UIUC and lead author of the study. "Our device can hide a complex 3D object in an infinite number of directions while keeping the temperature inside stable and protected."

The breakthrough came from rethinking the fundamental material requirements. The team went back to the theory of transformation thermotics and asked what kind of material structure could cover almost all the thermal properties needed for a perfect cloak. Their answer was a new type of lattice-based material that can be freely adjusted in three dimensions.

The physical cloak is a hybrid structure: a precisely 3D-printed aluminum lattice that acts as a high-conductivity material, with mold-cast rubber filling the gaps to provide low thermal conductivity. This combination allows precise control over how different regions conduct heat, covering a much wider range of thermal conductivities than previous approaches.

In laboratory tests, researchers placed the device between hot and cold regions to create a temperature gradient. Using an infrared camera, they tracked how heat flowed around and through the cloak. From the outside, the temperature field appeared completely undisturbed — as if the hidden object did not exist. Inside the cloaked region, the temperature remained uniform and protected from external extremes.

The team went further by cloaking highly complex 3D geometries, including detailed head-like shapes — a level of geometric complexity no previous experimental thermal cloak has achieved.

"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."

Potential applications range from precisely managing heat around sensitive microchip components to military and defense uses such as hiding personnel or equipment from thermal detection. The technology could also protect critical assets operating in extreme temperature environments.

The research was conducted in collaboration with postdoctoral researcher Weichen Li, graduate student Yibo Wang, and Professor Ole Sigmund at the Technical University of Denmark. It was supported by the National Science Foundation, the Villum Foundation, and the Air Force Office of Scientific Research.

Looking ahead, the team plans to explore smart and multifunctional cloaks that can not only hide objects but also actively manipulate heat on demand — concentrating, spreading, or guiding thermal energy within the protected region as needed.

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