Thermal "invisibility cloak" could keep people cool
A new thermal "invisibility cloak" that channels heat around whatever it is trying to hide may one day help keep people and satellites cool, researchers say.
Invisibility cloaks, once thought of only as the province of "Harry Potter"or "Star Trek," work by smoothly guiding light waves around objects so the waves ripple along their original trajectories as if nothing were there to block them. Cloaking devices that redirect other kinds of waves, such as the acoustic waves used in sonar, are possible as well.
Previous research had developed cloaking devices that could hide objects from heat -- essentially making them thermally invisible. However, these cloaks could not be turned on and off. In addition, each of these cloaks had to be tailored to whatever item they were cloaking. [Now You See It: 6 Tales of Invisibility in Pop Culture]
"In realistic cloaking applications, the environment changes; the object to be cloaked changes; everything changes,"study co-author Baile Zhang, a physicist and electrical engineer at Nanyang Technological University in Singapore, told Live Science. "Therefore, a controllable cloak that can adjust its performance is very desirable."
Now, Zhang and his colleagues have developed an active thermal cloak that can be switched on and off and can change its shape without affecting its performance.
The cloak is made up of 24 devices known as thermoelectric modules, which serve as heat pumps, moving heat from one place to another. Each of these small devices measures 0.24 by 0.24 by 0.15 inches (6 by 6 by 3.8 millimeters).
When the cloak is turned on, it redirects heat around an air hole that is 2.44 inches (62 mm) wide in a steel plate just 0.2 inches (5 mm) thick. It can prevent heat from diffusing through the hole across temperatures ranging from 32 to 140 degrees Fahrenheit (0 to 60 degrees Celsius). The heat pumps can also be rearranged to shield a rectangular hole 2.36 inches (60 mm) wide just as effectively, the researchers said.
This so-called active thermal cloak could, in principle, be made as thin as skin, Zhang said. It could help protect sensitive electronic components on microchips -- such as mobile devices, high-power engines and magnetic resonance imaging (MRI) scanners -- from the heat, the researchers said.
"The active thermal cloak might also be applied in human garments for effective cooling and warming, which makes a lot of sense in tropical areas such as Singapore," Zhang said in a statement. Other applications may include shielding satellites that need to change shape over time, he added -- say, by unfolding antennas.
But the futuristic technology is still in its infancy, Zhang said.
"Although the current work shows the possibility of controllable thermal cloaking, it's not an off-the-shelf product, and it will take years to incorporate this work into current heat-dissipation technologies," he added.
The researchers plan to improve the active thermal cloak's efficiency at transferring heat, which is currently about as good as that of a refrigerator, Zhang said. In addition, they are "currently considering placing sensors on the cloak, such that the cloak can sense the temperature of the environment and adjust its cloaking performance automatically," he said.
The scientists detailed their findings online Sept. 21 in the journal Applied Physics Letters.