Thermal cloak hides heat

Ashley N. Paddock, ashley.paddock@photonics.com

In a new approach to invisibility cloaking, French researchers propose isolating or cloaking objects from sources of heat – essentially “thermal cloaking.”

The method, developed by Sebastien Guenneau and his colleagues at Centre National de la Recherche Scientifique (CNRS), taps into some of the same principles as optical cloaking. Ultimately, it could lead to novel ways to control heat in electronics.

“Our key goal with this research was to control the way heat diffuses in a manner similar to those that have already been achieved for waves, such as light waves or sound waves, by using the tools of transformation optics,” Guenneau said.

Until now, cloaking research revolved around manipulating wave trajectories, such as electromagnetic (light), pressure (sound), elastodynamic (seismic) and hydrodynamic (ocean) waves. Guenneau’s study of heat, he points out, focuses on the physical phenomenon of diffusion, rather than wave propagation.

This figure shows that the object in the center of the cloak (letters OSA) stays cold, while the heat diffuses elsewhere. The source of the heat, which is at a constant temperature of 100 °C, is on the left-hand side, while the material inside the invisibility region remains cold. Courtesy of Sebastien Guenneau, Institut Fresnel, CNRS/AMU.

“Heat isn’t a wave – it simply diffuses from hot to cold regions,” he said. “The mathematics and physics at play are much different. For instance, a wave can travel long distances with little attenuation, whereas temperature usually diffuses over smaller distances.”

The CNRS team designed its cloak so that heat diffuses around an invisibility region, which is protected from heat. The researchers also can force heat to concentrate in a small volume, which will then heat up rapidly.

The ability to shield an area from heat or to concentrate it is highly desirable for a range of applications. Shielding nanoelectronic and microelectronic devices from overheating, for example, is one of the biggest challenges facing the electronics and semiconductor industries; thermal cloaking could have a tremendous impact on these sectors. As for the ability to concentrate heat, this could prove useful to the solar industry. On a larger scale and far into the future, thermal cloaking could be helpful for protecting large computers and spacecraft.

Guenneau’s team is working to develop prototypes of its thermal cloaks for microelectronics, which are expected to be ready within the next few months.

The method appears in OSA’s open-access journal Optics Express.