Assembled design of unit-cell thermal shifters for multipurpose thermal metamaterials.

The metamaterial is an artificial material which has distinctive physical properties that are not shown in nature. Among various physical characteristics, the optical metamaterials were mainly developed to make the cloaking or stealth functions in the artificial structures. Recently, transformation thermodynamics, which are derived from the design method of optical metamaterials allows to develop thermal metamaterials, which can control heat flux actively in the specific structures. The representative functions of thermal metamaterials were thermal shield, concentrator, diffuser, and inverter, and they were formed by the patterned metal plates. However, thermal metamaterials have been limited by the complex-cylindrical geometry because the active control of heat flux needs the continuous changes of thermal conductivity and local focusing or dissipation of thermal energy. Herein, we resolve the intrinsic limitations of geometries of thermal metamaterials, by means of the assembly design of thermal shifters. A thermal shifter is a patterned metal structure which can distort heat flux in one inclined direction. The heat flow in thermal metamaterials can be divided into tiny square areas, which are replaced with unit-cell thermal shifters, similar to pixels of two-dimensional images. In this work, the designed assembly of thermal shifters successfully form the multipurpose thermal metamaterials, such shield, concentrator, diffuser and inverter. The effectiveness of the assembly concept is evaluated in simulation and experimental verification.