Acoustic forces arising from high-frequency surface acoustic waves (SAW) underpin an exciting range of promising techniques for non-contact manipulation of fluid and objects at micron scale. Despite increasing significance of SAW-driven technologies in microfluidics, the understanding of a broad range of phenomena occurring within an individual SAW system is limited. Acoustic effects including streaming and radiation force fields are often assumed to result from wave propagation in a simple planar fashion. The propagation patterns of a single SAW emanating from a finite-width source, however, cause a far richer range of physical effects. In this work, we seek a better understanding of the various effects arising from the incidence of a finite-width SAW beam propagating into a quiescent fluid. Through numerical and experimental verification, we present five distinct mechanisms within an individual system. These cause fluid swirling in two orthogonal planes, and particle trapping in two directions, as well as migration of particles in the direction of wave propagation. For a range of IDT aperture and channel dimensions, the relative importance of these mechanisms is evaluated.

中文翻译：

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微流体系统中表面声波衍射驱动的机制†

高频表面声波（SAW）产生的声力为微米级的流体和物体的非接触式处理提供了令人兴奋的一系列有前途的技术。尽管SAW驱动技术在微流体中的重要性日益提高，但对单个SAW系统中发生的各种现象的理解仍然有限。通常认为包括流场和辐射力场在内的声学效应是由波以简单平面方式传播引起的。但是，从有限宽度源发出的单个声表面波的传播方式会引起更广泛的物理影响。在这项工作中，我们寻求更好地理解传播到静态流体中的有限宽度SAW光束的入射所产生的各种影响。通过数值和实验验证，我们介绍了单个系统中的五种不同机制。这些导致流体在两个正交平面中涡旋，并在两个方向上捕获粒子，以及在波传播方向上迁移粒子。对于一定范围的IDT孔径和通道尺寸，评估了这些机制的相对重要性。