Magnitude and Variance of Acoustic Energy Density in Microchannel Acoustophoresis:comparison between Single-frequency and Frequency-modulated Actuation

Using a novel light-intensity method, we quantify for the first time the magnitude and spatial variance in acoustic energy density along a microchannel during acoustophoretic focusing of particles with frequency-modulated ultrasound. We compare the distribution in energy density between single-frequency (SF) and frequency-modulation (FM) actuation along the microchannel. In addition, we analyze the field uniformity for the two actuation approaches (SF and FM) by measuring the deviation of the final particle pattern from an ideal straight line. We conclude that the magnitude of the energy density for FM actuation is of the same order of magnitude as for SF actuation, but with much less spatial variance.