Particle Deflection in a Poly(dimethylsiloxane) Microchannel Using a Propagating Surface Acoustic Wave: Size and Frequency Dependence

We study the effect of a propagating surface acoustic wave (PSAW) with different frequencies on particles with different sizes in microfludic channels. We find that the deflection critically depends on the applied frequency as well as on the particle size. For fixed frequencies, large particles are deflected and migrate perpendicular to the flow direction while smaller particles only follow the streamlines of the flow field. However, with increasing frequency of the PSAW above a size dependent limit, small particles are also actuated. This relation can be characterized by the wavenumber k and the particle radius r using the parameter kappa = k.r. For the onset of deflection, we find a critical value kappa(c) congruent to 1.28 +/- 0.20. Finally, we demonstrate how this device can be used for particle separation.