The positional stability of acoustically levitated droplets in air and the settling time of droplet positions on loading are important for precision applications of acoustic levitation. We therefore study their dependence on ultrasound pressure for droplets with diameters 0.01–0.2 times the acoustic wavelength in a single-axis acoustic levitator operating at 39 kHz. We find that the observed resonance frequencies agree well with theory. However, the damping coefficients of the oscillations exhibit large anisotropy, and their dependence on the droplet size deviates greatly from the behavior expected from the Stokes coefficient. These results suggest that acoustic streaming plays an important role in the motion of acoustically levitated droplets.
Oscillation resonances and anisotropic damping of the motion of acoustically levitated droplets in single-axis acoustic levitators
Soichiro Tsujino, Yohei Sato, Yasushi Takeda, Takashi Tomizaki; Oscillation resonances and anisotropic damping of the motion of acoustically levitated droplets in single-axis acoustic levitators. Appl. Phys. Lett. 29 July 2019; 115 (5): 053702. https://doi.org/10.1063/1.5112109
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