Designing effective thermal conductivity of materials of core-shell structure: Theory and simulation.

We introduce the phenomenon of golden touch from myth to thermotics. We define golden touch as extending the core property to a shell with an extremely small core fraction. We obtain the requirement of golden touch by making the effective thermal conductivity of the core-shell structure equal to the thermal conductivity of the core. We summarize three types (A, B, and C) of golden touch in two dimensions, and only two types (A and B) of golden touch in three dimensions. We theoretically analyze the distinct properties of different types of golden touch by delicately designing the anisotropic thermal conductivity of the shell. Golden touch is also validated by finite-element simulations which echo the theoretical analyses. Golden touch has potential applications in thermal camouflage, thermal management, etc. Our work not only lays the foundation for golden touch in thermotics, but also provides guidance for exploring golden touch in other diffusive fields like electrostatic and magnetostatic fields.