Three-dimensional omnidirectional acoustic orbital angular momentum emitter with tunable focus

Compared to plane waves, acoustic vortex (AV) beams exhibit broad application potential by exploring orbital angular momentum (OAM) degree of freedom. AV beams not only enhance the communication capacity but also provide an alternative for acoustic field engineering. Consequently, the development of high-intensity, low-sidelobe, and highly directional AV beams has become a challenge in the progression of OAM-based acoustic technologies. In this work, we propose an approach based on the simplified sectorial transducer array, with multiple cascaded discrete acoustic lenses (DALs) of designated phase modulation profiles that are placed sequentially before the transducer. AV beams emitted by the transducer array, after undergoing phase modulation of cascaded DALs, form focused acoustic vortex (FAV) beams. By tuning the orientation angle of each DAL, the focal point can be freely translated within full three-dimensional space. In addition, by adjusting the phase delay of the sectors of transducer array, the topological charge of FAV beams can be switched during the movement of the focal point, i.e., the vortex center. This approach addresses the high-cost issue associated with the extensive use of active components in traditional methods, while simplifying the fabrication of various passive devices. It holds wide potential in particle manipulation and acoustic communication.