Acoustic Pseudo-Vortices with Zero Orbital Angular Momentum
Affiliation Type:
Academia
Keywords:
Acoustic Levitation, Phased Array, Vortex
Abstract:
An acoustic vortex beam can be used to manipulate objects in various media, however, the orbital angular momentum (OAM) transfer can cause instability. We present a novel type of acoustic pseudo-vortices characterized by zero OAM and demonstrate how to induce OAM in a controllable fashion. Acoustic pseudo-vortices are generated by superposing two vortices with opposite topological charges to create a petal-like acoustic pressure pattern. The experiments and finite element simulations confirm the stable levitation of a sphere in mid-air. To induce OAM transfer we present three strategies: stepwise, via pseudo-vortex rotation itself; and continuous, by detuning the ratio of two opposite vortices or by changing their relative topological charges. The pseudo-vortices open up new applications where OAM transfer is undesirable or needs to be controlled precisely while offering similar acoustic radiation force as normal vortices.
