High-energy-density acoustofluidic device using a double-parabolic ultrasonic transducer

High-acoustic-energy-density acoustofluidic devices are necessary to make this technology a viable option for clinical applications in the biomedical field. We present a mechanical interface that enables delivery of a high-amplitude acoustic field inside a fluid cavity by translating the vibrations from two large piezoelectric elements into a microfluidic chip. The study comprises both experimental characterization of a double-parabolic metallic acoustic waveguide and simulations of its working mechanism in two dimensions. We could focus 4.9-µm polystyrene particles at a flowrate of 5 ml/min, corresponding to an average retention time of 13.5 ms for particles in the actuated area. Moreover, we measured the acoustic energy density in the channel at stopped-flow condition, obtaining an average value of 1207 J/m3 and a maximum value of 2977 J/m3 with an input electrical power of 1.5 W. By comparing the simulation results with laser-Doppler vibrometer measurements, we confirmed that transverse sound waves play a significant role in the working mechanism of the double-parabolic structure, thus paving the way for further future optimization of the waveguide design.