Researchers at the University of Illinois Urbana-Champaign and the Technical University of Denmark have developed a three-dimensional thermal cloak that can conceal objects from infrared cameras while protecting them from extreme temperatures.
The device guides heat around an object so that its thermal signature appears indistinguishable from the surrounding environment. Unlike previous experimental designs that operated primarily in two dimensions or worked only when heat flowed from a particular direction, the new cloak functions from essentially any direction.
The researchers said the technology could eventually support thermal management for electronics and microchips, protection of equipment in extreme environments, and security or defense applications involving infrared detection.
The study was led by University of Illinois civil and environmental engineering professor Shelly Zhang, postdoctoral researcher Weichen Li and graduate student Yibo Wang, in collaboration with Technical University of Denmark professor Ole Sigmund.
Their findings were published in the journal Nature Communications.
Thermal cameras detect differences in infrared radiation associated with temperature. An object typically becomes visible when its temperature differs from the area around it.
Rather than simply placing an insulating barrier around an object, a thermal cloak must redirect heat in a controlled manner. Heat must flow around the protected region and reconnect on the other side without creating a detectable disturbance in the surrounding temperature field.
The researchers returned to the theoretical principles of transformation thermotics, a field focused on controlling heat flow through specially designed materials.
They sought to create a material structure capable of reproducing the wide range of thermal properties required for an effective three-dimensional cloak.
The team developed a lattice-based material whose structure can be adjusted independently along three directions. By modifying the dimensions and configuration of different sections of the lattice, the researchers can control how effectively heat travels through each region of the cloak.
This approach provides a broader range of thermal conductivity than previous experimental designs and more closely reproduces the properties required by theoretical models of ideal thermal cloaking.
The device combines materials with substantially different thermal characteristics.
The researchers used 3D-printed metal to create a precisely engineered aluminum lattice. Aluminum conducts heat efficiently, allowing thermal energy to move through selected areas of the structure.
They then used mold casting to fill sections of the device with a rubber-like material that has low thermal conductivity.
The combination of highly conductive aluminum and insulating rubber enabled the researchers to guide heat through the cloak’s three-dimensional structure.
During laboratory testing, the team placed the device between hot and cold regions to create a temperature gradient. An infrared camera was used to observe how heat traveled through and around the cloak.
From outside the device, the resulting temperature pattern appeared similar to what would have been observed if no hidden object were present.
At the same time, the temperature within the cloaked region remained relatively uniform and was protected from the surrounding hot and cold conditions.
The ability to maintain a stable internal temperature gives the technology potential applications beyond concealment.
A thermal cloak could protect sensitive electronics or other components from damaging temperature changes while directing heat through the surrounding environment.
The researchers also tested the technology with complicated three-dimensional shapes, including detailed head-like geometries.
They said earlier experimental thermal cloaks had not demonstrated a comparable combination of geometric complexity, omnidirectional performance and physical testing.
Potential electronics applications include managing heat around processors, batteries, sensors and other temperature-sensitive components.
As computing systems become smaller and more powerful, controlling the movement of heat has become an increasingly important engineering challenge. Excess heat can reduce device performance, shorten component lifespans and contribute to equipment failure.
A precisely engineered thermal material could redirect heat away from sensitive areas while maintaining desired temperatures within protected regions.
The technology could also be used to shield equipment from extreme external conditions, including environments where components are exposed to nearby heat sources or large temperature differences.
Security and defense applications could involve reducing the thermal visibility of people, vehicles or equipment to infrared imaging systems.
However, the current system primarily redirects heat originating outside the cloaked area. Additional work would be required to conceal an object that produces substantial heat of its own.
A person, engine, electronic system or other active heat source would continuously release thermal energy inside the cloak. Masking that energy would require a more advanced structure capable of collecting, distributing or redirecting internally generated heat.
The researchers plan to investigate smart and multifunctional cloaks that could adjust their thermal properties or actively manipulate heat based on changing conditions.
Future versions could potentially concentrate heat in selected locations, spread it across a larger area or guide it along different paths on demand.
The work was supported by the National Science Foundation, the Villum Foundation and the Air Force Office of Scientific Research.
KEY QUOTES:
“A real thermal cloak should work no matter where the heat comes from. Our device can hide a complex 3D object in an infinite number of directions while keeping the temperature inside stable and protected.”
Shelly Zhang, Professor of Civil and Environmental Engineering at the University of Illinois Urbana-Champaign
“Any field that needs precise control of heat or needs to protect something from being detected thermally could benefit from this work. But we also see it more broadly: it’s about hiding and protecting information that is carried by heat.”
Shelly Zhang, Professor of Civil and Environmental Engineering at the University of Illinois Urbana-Champaign
“We’ve shown that a true 3D omnidirectional thermal cloak is possible. The next step is to make cloaks that don’t just hide and protect, but also actively manipulate heat in useful ways.”
Shelly Zhang, Professor of Civil and Environmental Engineering at the University of Illinois Urbana-Champaign
