Active thermal cloak hides a circular object in conductive heat flow by “pumping” heat from hot end to cold end. Credit: Xu & Zhang/NTU
Light, sound, and now, heat – just as optical invisibility cloaks can bend and diffract light to shield an object from sight, and specially fabricated acoustic metamaterials can hide an object from sound waves, a recently developed thermal cloak can render an object thermally invisible by actively redirecting incident heat.
The system, designed at NTU, Singapore, has the potential to fine-tune temperature distribution and heat flow in electronic and semiconductor systems. It has application in devices with high requirements for efficient dissipation and homogenous thermal expansion, such as high-power engines, MRI instruments, and thermal sensors.
“Because of its shape flexibility, 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,” said Prof. Baile Zhang of NTU.
To construct their active thermal cloak, they deployed 24 small thermoelectric modules, which are semiconductor heat pumps controlled by an external input voltage, around a 62-millimeter diameter air hole in a carbon steel plate just 5 mm thick. The modules operate via the Peltier effect, in which a current running through the junction between 2 conductors can remove or generate heat. When many modules are attached in series, they can redirect heat flow. The researchers attached the bottom and top ends of the modules to hot and cold surfaces at 60° C and 0° C respectively, to generate a diffusive heat 3flux.
When the researchers applied a variety of specific voltages to each of the 24 modules, the heat falling on the hot-surface side of the air hole was absorbed and delivered to a constant-temperature copper heat reservoir attached to the modules. The modules on the cold-surface side released the same amount of heat from the reservoir into the steel plate. This prevented heat from diffusing through the air hole, which can be used to shield sensitive electronic components from heat dissipation.
Additionally, they found that their active thermal cloaking was not limited by the shape of the object being hidden. When applied to a rectangular air hole, the thermoelectric devices redistributed heat just as effectively as in the circular one.
Looking ahead, Zhang and his colleagues plan to apply the thermal cloaks in electronic systems, improving the efficiency of heat transfer, and develop an intelligent control system for the cloak. http://www.alphagalileo.org/ViewItem.aspx?ItemId=156426&CultureCode=en
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