Thermal metamaterial for convergent transfer of conductive heat with high efficiency

It is crucially important to focus conductive heat in an efficient way, which has received much attention in energy science (say, solar cells), but is still far from being satisfactory due to the diffusive (divergent) nature of the heat. By developing a theory with hybrid transformations (rotation and stretch-compression), here we provide theoretical and experimental evidences for a type of thermal metamaterial called thermal converger. The converger is capable of convergently conducting heat in contrast to the known divergent behavior of heat diffusion, thus yielding a large heating region with high temperatures close to the heat source (high efficiency). The thermal converger further allows us to design a thermal grating—a thermal counterpart of optical grating. This work has relevance to heat focus with high efficiency, and it offers guidance both for efficient heat transfer and for designing thermal-converger-like metamaterials in other fields, such as electrics/magnetics, electromagnetics/optics, acoustics, and particle diffusion.