Centre for Audio, Acoustics and Vibration, University of Technology Sydney, Sydney, Australia.
Mechanical Engineering Department, National University of Singapore, Singapore 117575, Singapore.
Lab Chip. 2022 Sep 13;22(18):3290-3313. doi: 10.1039/d2lc00447j.
The motion of small objects in acoustophoresis depends on the acoustic radiation force and torque. These are nonlinear phenomena originating from wave scattering, and consist of primary and secondary components. The primary radiation force is the force acting on an object due to the incident field, in the absence of other objects. The secondary component, known as acoustic interaction force, accounts for the interaction among objects, and contributes to the clustering patterns of objects, as commonly observed in experiments. In this tutorial, the theory of acoustic interaction forces is presented using the force potential and partial-wave expansion approaches, and the distinguishing features of these forces such as rotational coupling and non-reciprocity are described. Theoretical results are compared to experimental measurements of interaction forces using a glass micro-capillary setup to explain the practical challenges. Finally, the phenomenon of clustering patterns induced by the close-range interaction of objects is demonstrated to point out the considerations about multiple collision and the predicted clustering patterns entirely due to the interaction force. Understanding the principles of acoustic interaction enables us to develop novel acoustofluidic applications beyond the typical processing of large populations of particles and with focus on the controlled manipulation of small clusters.
微流控中的声悬浮运动取决于声辐射力和力矩。这些非线性现象源自波散射，包括初级和次级分量。初级辐射力是指在不存在其他物体的情况下，物体因入射场而受到的力。次级分量，即声相互作用力，是指物体之间的相互作用，这导致了物体的聚集模式，这在实验中很常见。在本教程中，使用力势和分波展开方法介绍了声相互作用力的理论，并描述了这些力的旋转耦合和非互易性等特点。通过使用玻璃微毛细管装置进行实验测量，将理论结果与相互作用力进行了比较，以解释实际挑战。最后，通过近距离物体相互作用引起的聚集模式现象，说明了需要考虑多次碰撞，以及完全由相互作用力预测的聚集模式。理解声相互作用的原理可以帮助我们开发新型的声流控应用，超越对大量粒子的典型处理，并侧重于对小簇的控制操作。
