Acoustic mixing at low Reynold's numbers

In microfluidic devices, hydrodynamic flow is usually governed by very low Reynold's numbers. Under these conditions, only laminar flow is possible. Hence, mixing in microfluidics occurs by diffusion only. Interaction of small fluid volumes and acoustic waves in a solid leads to pronounced streaming effects in the fluid inducing mixing and stirring even at low Reynold's numbers. We demonstrate the applicability of such acoustically induced mixing in a variety of different microfluidic geometries, including planar and conventional three-dimensional microfluidic devices.