Thermal illusion with the concept of equivalent thermal dipole

The research on thermal illusion contributes to both fundamental theories and practical applications. In the existing literatures, the most common mechanism is to design a shell to disguise the inside core. However, the core-shell scheme may be weak to handle many-particle systems because N particles may require N specially-designed shells. This lacks efficiency and restricts practical applications. To solve this problem, we can no longer focus on the local effect of a single particle. In contrast, we should study the macroscopic effect of the N particles by treating each particle as an equivalent thermal dipole. Then, thermal illusion can be achieved when the macroscopic equivalent thermal dipole moments of different systems are equal to each other. This requires only once calculation and contributes to efficiency. Accidentally, the concept of equivalent thermal dipole helps to revisit the well-known Bruggeman theory and provides a clear physical image for it. The proposed scheme is verified by theoretical analyses, finite-element simulations, and laboratory experiments. Our work offers an efficient approach to achieving thermal illusion in many-particle systems, and contributes to potential applications in misleading infrared detection, manipulating heat flux, etc. Graphical abstract