Abstract

A thermal invisibility cloak, as inspired by optical invisibility cloaks, is a device which can steer the conductive heat flux around an isolated object without changing the ambient temperature distribution so that the object can be “invisible” to external thermal environment. While designs of thermal invisibility cloaks inherit previous theories from optical cloaks, the uniqueness of heat diffusion leads to more achievable implementations. Thermal invisibility cloaks, as well as the variations including thermal concentrator, rotator, and illusion devices, have potentials to be applied in thermal management, sensing and imaging applications. Here, we review the current knowledge of thermal invisibility cloaks in terms of their design and implementation in cloaking studies, and their extension as other functional devices.

Highlights

  • Metamaterials are materials with designed artificial structures that exhibit unusual physical properties

  • While designs of thermal invisibility cloaks inherit previous theories from optical cloaks, the uniqueness of heat diffusion leads to more achievable implementations

  • Initial designs of thermal invisibility cloaks started from the coordinate transformation method as inspired by the idea of optical invisibility cloaking

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Summary

INTRODUCTION

Metamaterials are materials with designed artificial structures that exhibit unusual physical properties. The idea of cloaking (guiding field and energy flux around an object) has been extended to other physical disciplines[19] including thermodynamics,[20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37] acoustics,[38,39] and mechanics.[40] Compared with electromagnetic waves which carry phase, the manipulation of heat flux is comparably easier due to its diffusion nature that involves no phase This means that the first practical cloaking technology is likely to be achieved in heat flux manipulation which is relevant to electronic and energy industries as well as military applications. Besides the thermal invisibility cloak, other thermal devices have been proposed with interesting functionalities such as the thermal concentrator,[25,29,30,31,37] rotator[25,30,36] and thermal camouflage.[32,33] In this review, we will summarize general thermal cloaking approaches, different designs and experimental implementations of thermal invisibility cloaks, as well as their extension including thermal concentrator, thermal rotator and thermal camouflage

APPROACHES
Coordinate transformation approach
Scattering cancellation approach
DESIGN AND IMPLEMENTATION
Thermal concentrator
Thermal rotator
Thermal illusion devices
CONCLUSION AND OUTLOOK
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