Enhancement of Acoustic Energy Density in Bulk-Wave-Acoustophoresis Devices Using Side Actuation

A high acoustic energy density is required in the acoustic resonator to increase the throughput of acoustophoresis devices. In this study, through both experiments and numerical simulations, we find that the energy density in bulk-wave-acoustophoresis devices can be enhanced by actuating the device from the side. Based on qualitative free-flow focusing experiments, side actuation shows clear superiority to bottom actuation under various input powers and flow rates. Quantitative measurements using confocal microparticle image velocimetry confirm an increase by a factor of 4 in energy density using side actuation. Numerical simulations reveal that side actuation leads to significant symmetry breaking, which accounts for strong acoustic fields in the channel, and the device energy-conversion efficiency using side actuation is also higher than that using bottom actuation for different device aspect ratios. Submicrometer particle focusing is performed using an acoustophoresis device with side actuation and more than 90% of 500-nm-diameter particles are focused under a total flow rate of 30 μl/min at an input power of 235 mW, achieved without using a power amplifier.