Inverse thermal design of nanoporous thin films for thermal cloaking

In recent years, nanoporous thin films are widely studied as an effective way to improve the thermoelectric performance or manipulate the thermal transport within thin-film-based devices. In practice, nanoporous patterns can effectively cut off the heat flow and thus guide the thermal transport along the desired direction. However, a better design of these thermal devices is not addressed, such as thermal cloaking as the thermal counterpart for optical invisibility cloaks. In existing designs based on the Fourier's law, composite materials with varied structures are often introduced to achieve the required location-dependent thermal conductivities to distort the heat flux. At the micro-to nano-scale, such designs are difficult to be implemented and factors such as the interfacial thermal resistance must be further considered. In this work, inverse thermal designs of a nanoporous thin film are used to achieve the two-dimensional thermal cloaking, without introducing any other variation of the composition or material to tune the local thermal conductivity. This simple approach can be widely used for thin-film-based devices to protect heat-sensitive regions or function as thermal camouflaging devices. The proposed nanoporous structures can also be used to tune the local properties of a thin film for general applications, such as graded thermoelectric materials.