Robustly printable freeform thermal metamaterials

Thermal metamaterials can be used to manipulate heat flow but experimental fabrication is challenging. Here, the authors report robustly printable freeform thermal metamaterials to tackle this challenge by topology optimization and 3D printing. Thermal metamaterials have exhibited great potential on manipulating, controlling and processing the flow of heat, and enabled many promising thermal metadevices, including thermal concentrator, rotator, cloak, etc. However, three long-standing challenges remain formidable, i.e., transformation optics-induced anisotropic material parameters, the limited shape adaptability of experimental thermal metadevices, and a priori knowledge of background temperatures and thermal functionalities. Here, we present robustly printable freeform thermal metamaterials to address these long-standing difficulties. This recipe, taking the local thermal conductivity tensors as the input, resorts to topology optimization for the freeform designs of topological functional cells (TFCs), and then directly assembles and prints them. Three freeform thermal metadevices (concentrator, rotator, and cloak) are specifically designed and 3D-printed, and their omnidirectional concentrating, rotating, and cloaking functionalities are demonstrated both numerically and experimentally. Our study paves a powerful and flexible design paradigm toward advanced thermal metamaterials with complex shapes, omnidirectional functionality, background temperature independence, and fast-prototyping capability.

Automated summary

This study introduces printable freeform thermal metamaterials to address long-standing challenges in manipulating heat flow. Using topology optimization based on local thermal conductivity tensors, different functional cells are designed and 3D printed for concentrator, rotator, and cloak metadevices. The omnidirectional concentrating, rotating, and cloaking functionalities of these thermal metadevices are demonstrated numerically and experimentally, paving the way for advanced thermal metamaterials with complex shapes and fast-prototyping capability.