Acoustic manipulation dynamics of levitated particle with screw-shaped reflecting surface

Existing single-axis acoustic levitation devices with an axisymmetric reflector can manipulate particles in a variety of ways. However, the mechanism by which particles are suspended in a single-axis acoustic levitator with a non-axisymmetric reflector remains poorly understood. This work addresses this issue by proposing a novel single-axis ultrasonic levitator design that includes a flat plane emitter and a screw-plane reflector. The node positions of the standing wave formed in this levitator were predicted by calculating the Gor'kov potential according to a numerical model. The analysis results demonstrate that the nodes were distributed off-axis and their positions varied in a spiral manner when changing the distance between the emitter and reflector. Corresponding experiments based on the proposed design were also conducted, and the results indicated that the distance changes between the emitter and reflector could induce some spiral trajectories of a polyethylene-foam particle placed in the ultrasonic field. Moreover, the trajectory of the suspended particle was found to distribute along a conical surface centered on the central axis of this device. This work provides a new approach for ultrasonic particle manipulation by changing the geometry of the reflector.