In recent years, scientists have developed the ability to manipulate light around an object through the use of man-made “metamaterials,” rendering the object seemingly invisible. Now, researchers from the Karlsruhe Institute of Technology (KIT) in Germany have demonstrated the similar ability to manipulate the flow of heat across a sheet of metal to hide a defect in the sheet.
The project is based on the theory for rendering a two-dimensional object invisible to time-varying temperature changes proposed by Sebastien Guenneau and colleagues of Marseille University, France in 2012. Guenneau assisted with the experiment at KIT.
A structure consisting of a 5-centimeter wide copper disc surrounded by concentric copper rings connected with thin spokes of copper was constructed for the experiment by cutting grooves and holes in the copper sheet and filling them with a rubbery thermal insulator. According to the research team, such a design allows heat to flow easily around the rings, but slowly in the radial direction.
“For the thermal invisibility cloak, both materials have to be arranged smartly,” Robert Schittny, co-author of the study published in the Physical Review Letters journal, said. “By providing a thin copper plate with annular silicon structures, we produce a material that conducts heat in various directions at variable speeds. In this way, the time needed for passing around a hidden object can be compensated.”
Researchers were able to determine that the complex ring structure distributed heat similar to the way an unaltered copper sheet would using an infrared camera to record the flow of heat across the structure while one side of the structure was submerged in hot water and the other side in room temperature water.
The experiment also demonstrated how important the complex ring structure is to the success of thermal cloaking, since simply insulating the central disk from the rest of the sheet resulted in a different temperature profile.
In the future, such a structure could be used for more effective heat management in microchips, electric components or machines.
“These results impressingly reveal that transformation optics methods can be transferred to the highly different area of thermodynamics,” Martin Wegener, head of the Institute of Applied Physics of KIT, said. “I hope that our work will be the basis of many further developments in the field of thermodynamic metamaterials.”