Dynamic characteristics of acoustic levitation under probe manipulation

Based on a protype that combines a single-axis acoustic levitator with a cylindrical probe, the kinematic and dynamic characteristics of an acoustically levitated spherical sample are studied when the probe enters and exits the sound field horizontally. The experiment shows that, within a certain distance, the approaching of the probe increases the vibration amplitude and reduces the vibration frequency of the levitated sample, and has an attraction effect on the sample. The critical detachment distance when the probe exits the sound field is larger than the critical attachment distance when it enters the sound field, showing a hysteresis effect. The critical attachment distance and the critical detachment distance are both proportional to the probe diameter. The finite element calculation reveals the mechanism of the attraction effect is the non-axisymmetric distribution of sound field induced by the probe, which produces a net component of acoustic radiation force directed towards the probe. The calculation also reveals the influence of probe position and diameter on the maximum offset distances of the sample and the frequency of horizontal vibration, which is consistent with the experimental results.