A transient thermal cloak experimentally realized through a rescaled diffusion equation with anisotropic thermal diffusivity

Abstract

Transformation optics has made a major contribution to the advancement of modern electromagnetism and related research assisted by the development of metamaterials. In this work, we applied this concept to the thermodynamics using the coordinate transformation to the time-dependent heat diffusion equation to manipulate the heat flux by predefined diffusion paths. Experimentally, we demonstrated a transient thermal cloaking device engineered with effective thermal materials and successfully hid a centimeter-sized vacuum cavity. A rescaled heat equation accounting for all the pertinent parameters of various ingredient materials was proposed to greatly facilitate the fabrication. Our results unambiguously demonstrate the practical possibility of implementing complex transformed thermal media with high accuracy and acquiring several unprecedented thermodynamic functions, which we believe will help to broaden the current research and pave a new path to manipulate heat for novel device applications. In this work, transformation optics technique was applied to the thermodynamic area by using the coordinate transformation to the time-dependent heat diffusion equation, which enables the manipulation of the heat flux by predefined diffusion paths. A transient thermal cloaking device engineered with effective thermal materials was experimentally demonstrated by hiding a centimeter-sized vacuum cavity. To facilitate the fabrication a rescaled heat equation taking into account of all the pertinent parameters of various ingredient materials was proposed to guide the practical design of complex transformed thermal devices. Metamaterials are complex materials carefully devised to exhibit specific properties that do not typically occur in nature. For example, in transformation optics, they can guide light along predefined paths to produce effects such as invisibility cloaking. In a Chinese-Swedish collaboration, Sailing He and co-workers have applied this same approach to thermodynamics to fabricate a thermal cloaking device. The researchers assembled constituent materials in a precise manner to form a centimeter-sized thermal cloak that successfully guided a heat flux along predefined diffusion paths. Such devices have previously been investigated but the calculations of these studies were based on the heat conduction equation, and the resulting heat manipulation could only be applied to materials in a thermostatic state. Instead, He and co-workers have taken into account the time-dependent rescaled heat diffusion equation, which uses anisotropic thermal diffusivity as the main factor, so that their multi-layered device can be implemented with high accuracy and works in a transient state.