Metamaterials for Manipulating Thermal Radiation: Transparency, Cloak, and Expander

Existing thermal metamaterials are mostly designed to work at room temperature, where thermal conduction is the dominant method of heat transfer. Unfortunately, as the temperature increases, thermal radiation becomes non-negligible, and hence these thermal metamaterials can no longer work. The inability to handle thermal radiation largely limits practical applications at high temperatures, such as thermal protection. To solve this problem, here we propose an effective-medium theory to manipulate thermal radiation with the Rosseland diffusion approximation. This theory helps to design three radiative metamaterials even with anisotropic geometries, including transparency, cloak, and expander. Theoretical analyses are further confirmed by finite-element simulations, which indicate that these radiative metamaterials behave well in both steady and transient states. This work not only offers an effective-medium theory to manipulate thermal radiation but also designs three radiative metamaterials. These results may provide hints for novel thermal management and have potential applications in radiative camouflage, radiative diodes, etc.