A thermal invisibility cloak that can make objects thermally invisible by redirecting incoming heat has been developed by Singaporean researchers.
Based on carefully engineered metamaterials – materials with properties that can’t be found in nature – the technology could potentially help improve the thermal performance of various electronic systems by fine-tuning thermal dissipation.
The team from the Nanyang Technological University (NTU) that developed the system has previously experimented with the so-called passive thermal cloaks capable of guiding conductive heat around a hidden object.
The team's latest invention is the first active thermal invisibility cloak with an on/off switch and the ability to be adapted to objects of varying geometries.
"We considered the question of whether we can control thermal cloaking electrically, not by guiding heat around the hidden object passively with traditional metamaterials, but by 'pumping' heat from one side of the hidden object to the other side actively, with thermoelectric modules," said Professor Baile Zhang, the lead researcher behind the project. The work is described in an article featured on the cover of the latest issue of the journal Applied Physics Letters.
Zhang said the device could help optimise the thermal performance of a large variety of electronic devices including high-power engines, magnetic resonance imaging 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," Zhang said.
The active thermal cloak consists of 24 small thermoelectric semiconductor heat pumps controlled by an external input voltage. These heat-pumps are distributed around a 62-millimeter diameter air hole in a carbon steel plate just 5mm thick.
When electrical current runs through the junction between two modules, the so-called Peltier effect kicks in and removes or generates heat.
In the experiments, the researchers attached the modules to two surfaces with temperatures of 60°C and 0°C. Subsequently, they applied a variety of specific voltages to each of the 24 modules and observed how 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.
Additionally, the researchers 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.