The cloak can conceal objects with a wide variety of 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 overcomes these restrictions by directing heat around a hidden object rather than simply blocking it. As a result, infrared imaging shows a temperature pattern that makes the object appear to be absent.

The research was conducted by University of Illinois Urbana-Champaign civil and environmental engineering professor Shelly Zhang, postdoctoral researcher Weichen Li, and graduate student Yibo Wang, in collaboration with professor Ole Sigmund of the Technical University of Denmark. Their findings were published in Nature Communications.

"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."

A New Material Makes 3D Thermal Invisibility Possible

Creating a thermal cloak that functions in three dimensions has been a longstanding challenge. Previous experimental devices could redirect heat only across a flat surface or along one direction of heat flow, leaving them far short of the capabilities needed for a fully three-dimensional cloak.

To overcome these limitations, the researchers revisited the foundational principles of transformation thermotics, a field that explores how heat can be redirected through specially designed materials. They focused on a central question: "What kind of material structure could cover almost all the thermal properties needed for a perfect cloak?"

The solution was a new lattice-based material whose structure can be independently adjusted along three directions. These changes allow the researchers to control how efficiently heat passes through different parts of the cloak. Compared with previous designs, the material can achieve a much broader range of thermal conductivities, closely approaching the properties predicted to be necessary for ideal thermal cloaking.

Importantly, the researchers went beyond computer simulations and constructed a working device. They used 3D metal printing to produce an intricate aluminum lattice, which 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, these materials create a structure that can carefully control the movement of heat.

Infrared Camera Tests Confirm the Cloak Works

To evaluate the device, the team positioned it between hot and cold regions, establishing a temperature difference that caused heat to flow through the surrounding environment. They monitored the resulting temperature patterns with an infrared camera to determine whether the cloak could successfully redirect heat around the concealed area.

The experiments showed that the device could guide heat around the hidden region while preserving the surrounding temperature pattern. To an infrared camera, the area appeared much as it would if no object were present. At the same time, temperatures inside the cloak remained uniform, shielding the concealed space from the extreme conditions outside.

The researchers also tested whether the cloak could accommodate unusually complicated objects. They successfully concealed intricate three-dimensional geometries, including detailed shapes resembling human heads. According to the team, earlier experimental thermal cloaks have not demonstrated a comparable combination of geometric complexity and cloaking performance.

Potential Applications in Electronics and Stealth Technology

The ability to control heat in three dimensions could have important implications across several industries. 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.

The researchers also see potential applications in security and defense. Future versions of the technology might help conceal people or equipment from thermal detection systems or shield valuable assets from severe temperature conditions. These uses would build on the device's demonstrated ability to redirect external heat while keeping the protected region thermally stable.

"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 Next Challenge Is Hiding Objects That Generate Heat

Although the current cloak represents a major advance, the researchers want to develop more sophisticated versions capable of performing additional functions. One particularly important goal is to conceal objects that produce heat themselves, rather than only protecting them from heat originating outside the cloak.

Achieving this would require materials that can actively control heat within the concealed region. Instead of simply redirecting incoming heat, a future cloak would need to concentrate, distribute, or guide thermal energy as conditions change. Such capabilities could expand the technology's usefulness in electronics, thermal protection, and applications involving infrared detection.

"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.