Thermal magnifier and external cloak in ternary component structure

Thermal metamaterials have aroused broad research interests for their potential applications in heat manipulation. Among them, bilayer thermal cloak is a representative one. However, the requirement of zero thermal conductivity of the inner layer may largely restrict broader applications. In this work, we remove the requirement of zero thermal conductivity and explore a ternary component structure. By calculating its effective thermal conductivity, we derive some special relations which result in two distinct camouflage behaviors, i.e., thermal magnifier and external cloak. Concretely speaking, thermal magnifier can thermally disguise a small object into a big one, and external cloak can thermally hide a component outside the cloak. Finite-element simulations are conducted in both two and three dimensions, which echo with our theoretical prediction. The ternary component structure has potential applications in thermal camouflage, thermal invisibility, etc. This work not only paves the way for designing camouflage in thermotics but also opens up an avenue for exploring camouflage in other diffusive fields like electrostatic, magnetostatic, and particle diffusive fields.