Controllable generation of acoustical vortices with sparse sources

A phase-coded approach is proposed to generate controllable acoustical vortices with sparse sources. The physical mechanism of acoustical vortices is theoretically investigated with explicit formulae. Axial and radial distributions of pressure and phase are investigated numerically and experimentally for different parameters using N sources. It is demonstrated that with proper design of source phases, acoustical vortices can be generated in homogeneous medium as a helical beam with circular pressure distribution and spiral acoustic wave front. Angular momentum transfer of acoustical vortices is also proved by the stable rotation of a hanging plate. The favorable results confirm the feasibility of controllable generation of acoustical vortices with sparse sources and suggest the application potential in object alignment or particle manipulation.