A Microfluidic Device Based on Standing Surface Acoustic Waves for Sorting and Trapping Microparticles

Microfluidic devices can provide innovative means to handle and control the transport of (bio)particles within a fluid flow. The advantage of microscale devices is that different components can be integrated in a single chip at low cost, with a negligible power consumption, compared to alternative solutions. In this work, a numerical investigation is developed on the use of standing surface acoustic waves (SAWs) generated within a microfluidic channel in order to manipulate microparticles. Far-field waves are generated via inter-digital transducers (IDTs), travel on the surface of a piezoelectric substrate and finally interfere in the channel, giving rise to a standing wave solution in terms of acoustic pressure. Results are reported for different geometries of the channel, to define the sensitivity of the acoustic pressure field to the relevant geometric features of the channel. This investigation shows how the acoustic radiation and drag forces interact with each other to move and focus the particles, possibly leading to a separation of heterogeneous ones, and generally provide a way to manipulate them at a small scale.