Controlling mass and energy diffusion with metamaterials

TL;DR

This paper reviews recent advances in using metamaterials to control diffusion processes like heat and particle transport, highlighting theoretical foundations, device applications, and future research directions.

Contribution

It categorizes and discusses the application of transformation and scattering cancellation theories in diffusion control across various energy and mass systems, introducing the concept of 'diffusionics.'

Findings

Metamaterials enable unprecedented control of diffusion processes.

Various devices like cloaks and radiative coolers have been developed.

Future directions include AI integration and topological approaches.

Abstract

Diffusion driven by temperature or concentration gradients is a fundamental mechanism of energy and mass transport, which inherently differs from wave propagation in both physical foundations and application prospects. Compared with conventional schemes, metamaterials provide an unprecedented potential for governing diffusion processes, based on emerging theories like the transformation and the scattering cancellation theory, which enormously expanded the original concepts and suggest innovative metamaterial-based devices. We hereby use the term "diffusionics" to generalize these remarkable achievements in various energy (e.g., heat) and mass (e.g., particles and plasmas) diffusion systems. For clarity, we categorize the numerous studies appeared during the last decade by diffusion field (i.e., heat, particles, and plasmas) and discuss them from three different perspectives: the theoretical perspective, to detail how the transformation principle is applied to each diffusion field; the application perspective, to introduce various intriguing metamaterial-based devices, such as cloaks and radiative coolers; and the physics perspective, to connect with concepts of recent concern, such as non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation. We also discuss the possibility of controlling diffusion processes beyond metamaterials. Finally, we point out several future directions for diffusion metamaterial research, including the integration with artificial intelligence and topology concepts.