Diffusion driven by temperature or concentration gradients is a fundamental mechanism of energy and mass transport that 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 that expanded the original concepts and suggested innovative metamaterial-based devices. The term diffusionics is used in the review to generalize these noteworthy achievements in various energy and mass diffusion systems. Examples include heat diffusion systems and particle and plasma diffusion systems. For clarity the numerous studies published over the past decade are categorized by diffusion field (i.e., heat, particles, and plasmas) and discussed 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 interesting metamaterial-based devices, such as cloaks and radiative coolers; and the physics perspective, to connect them with concepts of recent concern, such as non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation. The possibility of controlling diffusion processes beyond metamaterials is also discussed. Finally, several future directions for diffusion metamaterial research, including the integration of metamaterials with artificial intelligence and topology concepts, are examined.

中文翻译：

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用超材料控制质量和能量扩散

由温度或浓度梯度驱动的扩散是能量和质量传输的基本机制，在物理基础和应用前景方面与波传播有着本质上的不同。与传统方案相比，超材料为控制扩散过程提供了前所未有的潜力，其基础是变换和散射抵消理论等新兴理论，这些理论扩展了原始概念并提出了基于超材料的创新设备。评论中使用扩散学一词来概括各种能量和质量扩散系统中的这些值得注意的成就。例子包括热扩散系统以及粒子和等离子体扩散系统。为了清楚起见，过去十年发表的大量研究按扩散场（即热、粒子和等离子体）进行分类，并从三个不同的角度进行讨论：理论角度，详细说明如何将变换原理应用于每个扩散场；从应用角度，介绍各种有趣的基于超材料的器件，例如斗篷和辐射冷却器；和物理学的角度，将它们与最近关注的概念联系起来，例如非厄米拓扑、非互易传输和时空调制。还讨论了控制超材料之外的扩散过程的可能性。最后，研究了扩散超材料研究的几个未来方向，包括超材料与人工智能和拓扑概念的集成。