Ultrathin Three-Dimensional Thermal Cloak

We report the first experimental realization of a three-dimensional thermal cloak shielding an air bubble in a bulk metal without disturbing the external conductive thermal flux. The cloak is made of a thin layer of homogeneous and isotropic material with specially designed three-dimensional manufacturing. The cloak’s thickness is $100\mu \mathrm{m}$ 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 in a two-dimensional geometry. This work can find applications in novel thermal devices in the three-dimensional physical space.

Figure 1

Material candidates to realize a 3D thermal cloak with the background medium of stainless steel. The black curve shows the relative thermal conductivity required to implement a 3D thermal cloak with different thickness ratio of the cloak. The inset illustrates the cross section of the cloak (not to scale). Red or blue region denotes high or low temperature, and dashed arrows represent heat flux.

Figure 2

Fabrication of a 3D thermal cloak. (a) Molding process of half of the 3D thermal cloak: a thin copper disk is punched into the hemispherical hole in the stainless steel block. (b) Illustration and snapshot of half of the thermal cloak after molding. (c) Illustration and snapshot of the full cloak by combining two half blocks. The red or blue plate represents high or low temperature at the bottom and top surface.

Figure 3

Characterization of conductive thermal cloaking for transient homogeneous thermal flux. (a)–(c) Temperature distributions for the moment of 0.5 min in the beginning of heat transfer. (d)–(f) Temperature distributions for the moment of 4.5 min close to thermal equilibrium. (a) and (d) Temperature distributions in the pure background without any air bubble or cloak. (b) and (e) Temperature distributions when an air bubble is present without the cloak. (c) and (f) Temperature distributions when the air bubble is cloaked by the ultrathin cloak. In (b),(c) and (e),(f) the dotted circles indicate the position of the air bubble, while the dotted circles in (a) and (d) are merely for comparison.

Figure 4

Characterization of conductive thermal cloaking for an inhomogeneous temperature field from a point heat source. (a) Temperature distribution in the pure background without any air bubble or cloak. (b) Temperature distribution when an air bubble without the cloak is present close to the heat source. (c) Temperature distribution when the air bubble is cloaked by the ultrathin cloak. In (b),(c), the dotted circles indicate the position of the air bubble, while the dotted circle in (a) is merely for comparison.