Two-Dimensional Mapping Separating the Acoustic Radiation Force and Streaming in Microfluidics

In microscale fluids, fields of physical force and streaming play central roles in manipulating and tweezing objects, but it is difficult to disentangle and obtain accurate pictures of them. We develop a multiradius microparticle image velocimetry (MRμPIV) protocol to solve this problem in miniaturized spaces.

By using several monodisperse suspensions of spherical particles, each with its own specific particle radius, two-dimensional (2D) mapping separating the fields of radiation force and streaming is demonstrated in a microfluidic chamber driven by standing or focused surface acoustic waves, while motorized scanning is unnecessary and no special assumptions need to be made about the driving field.

The results also allow the extraction of other physical parameters such as the acoustic pressure amplitude. The principle of MRμPIV relies on a quasiequilibrium assumption for the particle motion and a linear dependence of the field force on particle volume. Therefore, it is also applicable to tweezing techonologies using optical, dielectrophoretic, and magnetic forces, constituting an extension of the PIV technique impactful for microscale physics in general.