Sound can exert forces on objects of any material and shape. This has made the contactless manipulation of objects by intense ultrasound a fascinating area of research with wide-ranging applications. While much is understood for acoustic forcing of individual objects, sound-mediated interactions among multiple objects at close range gives rise to a rich set of structures and dynamics that are less explored and have been emerging as a frontier for research. We introduce the basic mechanisms giving rise to sound-mediated interactions among rigid as well as deformable particles, focusing on the regime where the particles’ size and spacing are much smaller than the sound wavelength. The interplay of secondary acoustic scattering, Bjerknes forces, and micro-streaming is discussed and the role of particle shape is highlighted. Furthermore, we present recent advances in characterizing non-conservative and non-pairwise additive contributions to the particle interactions, along with instabilities and active fluctuations. These excitations emerge at sufficiently strong sound energy density and can act as an effective temperature in otherwise athermal systems.

中文翻译：

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多体结构和动力学的声学操纵


声音可以对任何材料和形状的物体施加力。这使得通过强超声波对物体进行非接触式操纵成为一个令人着迷的研究领域，具有广泛的应用。虽然对单个物体的声学作用有很多了解，但近距离多个物体之间的声音介导的相互作用产生了一组丰富的结构和动力学，这些结构和动力学较少被探索，并已成为研究的前沿。我们介绍了刚性颗粒和可变形颗粒之间产生声介导相互作用的基本机制，重点关注颗粒尺寸和间距远小于声波波长的情况。讨论了二次声散射、比耶克内斯力和微流的相互作用，并强调了颗粒形状的作用。此外，我们还介绍了表征粒子相互作用的非保守和非成对加性贡献以及不稳定性和主动波动的最新进展。这些激发以足够强的声能密度出现，并且可以在其他非热系统中充当有效温度。