The first experimental realization of a three-dimensional thermal cloak shielding an air bubble in a bulk metal without disturbing external thermal flux has been made. The cloak is made of a thin layer of homogeneous and isotropic material with simple mechanical manufacturing. The cloak’s thickness is 200 μm while the cloaked air bubble has a diameter of 1 cm, achieving the ratio between dimensions of the cloak and the cloaked object 2 orders smaller than previous thermal cloaks which were mainly realized at a two-dimensional plane. This work can find applications in novel thermal devices in the three-dimensional physical space. [Arxiv – Experimental demonstration of an ultra-thin three-dimensional thermal cloak]
Material candidates to realize a 3D thermal cloak with the background material of stainless steel. The black curve shows relative thermal conductivity required to implement a 3D thermal cloak with different thickness ratio of the cloak. The inset figure illustrates the cross section of the cloak. Red/ blue region denotes high/ low temperature, and dashed arrows represent the heat flux
Because an air bubble has nonzero thermal conductivity, its temperature will raise slowly rather than staying constant. This is a common observation in most of previous thermal cloak experiments up to date. However, the raise of temperature of the air bubble has little influence on the temperature distribution in the external region. Moreover, because of the slow rising speed of temperature inside the air bubble compared to the surrounding background, this cloak can still provide effective thermal protection for a relatively long time.
In conclusion we present the design, fabrication and experimental characterization of an ultra-thin 3D thermal cloak that can shield an air bubble in a bulk metal. To the best of our knowledge, it is the first realization of a thermal cloak in a 3D sphere. Because of its ultrathin thickness and simple manufacturing, this cloak can find wide cost-effective applications in addressing practical issues of distorted temperature distributions caused by air defects in mechanical engine systems and semiconductor devices
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