Scientists eye thermal cloaks for starships

A team of French researchers has proposed isolating or cloaking objects from sources of heat, a process they dub “thermal cloaking.”

According to Sebastien Guennea of the Centre National de la Recherche Scientifique (CRNS), thermal cloaking actually taps into some of the same principles as optical cloaking.

“Recent advances in invisibility cloaks are based on the physics of transformation optics, which involves metamaterials and bending light so that it propagates around a space rather than through it,” he explained.

“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.”

As Guennea notes, while thermal cloaking uses the same fundamental theories as recent advances in optical cloaking, there is one key difference. Until now, cloaking research has primarily revolved around manipulating trajectories of waves, including electromagnetic (light), pressure (sound), elastodynamic (seismic) and hydrodynamic (ocean) waves. 

The most significant difference in their study of heat, he points out, is that the physical phenomenon involved is diffusion, not wave propagation.

“Heat isn’t a wave – it simply diffuses from hot to cold regions… The mathematics and physics at play are much different,” he said.

“For [example], a wave can travel long distances with little attenuation, whereas temperature usually diffuses over smaller distances.”

As such, Guenneau and his team applied the mathematics of transformation optics to equations for thermal diffusion. In their two-dimensional approach, heat flows from a hot to a cool object with the magnitude of the heat flux through any region in space represented by the distance between isotherms (concentric rings of diffusivity). 

They then altered the geometry of the isotherms to make them go around – rather than through a circular region to the right of the heat source. Meaning, any object placed in this region can be shielded from the flow of heat.

“We can design a cloak so that heat diffuses around an invisibility region, which is then protected from heat. Or we can force heat to concentrate in a small volume, which will then heat up very rapidly,” Guenneau added.

The ability to shield an area from heat or concentrate thermal emissions are highly desirable traits for a wide range of applications. Shielding nanoelectronic and microelectronic devices from overheating, for example, is one of the biggest challenges facing the electronics and semiconductor industries, and an area in which thermal cloaking could have a huge impact.
 Of course, on a larger scale and far into the future, large computers and spacecraft could also benefit greatly.

So what’s next for Guenneau? Well, his team is now working to develop prototypes of their thermal cloaks for microelectronics, which they expect to have ready for testing within the next few months.