Multiple off-axis acoustic vortices generated by dual coaxial vortex beams**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474166 and 11604156), the Science and Technology Cooperation Projects of People’s Republic of China–Romania (Grant No. 42-23), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161013), the Postdoctoral Science Foundation of China (Grant No. 2016M591874), and the

Abstract

As a kind of special acoustic field, the helical wavefront of an acoustic vortex (AV) beam is demonstrated to have a pressure zero with phase singularity at the center in the transverse plane. The orbital angular momentum of AVs can be applied to the field of particle manipulation, which attracts more and more attention in acoustic researches. In this paper, by using the simplified circular array of point sources, dual coaxial AV beams are excited by the even- and odd-numbered sources with the topological charges of and based on the phase-coded approach, and the composite acoustic field with an on-axis center-AV and multiple off-axis sub-AVs can be generated by the superimposition of the AV beams for . The generation of edge phase dislocation is theoretically derived and numerically analyzed for . The numbers and the topological charges as well as the locations of the center-AV and sub-AVs are demonstrated, which are proved to be determined by the topological charges of the coaxial AV beams. The proposed approach breaks through the limit of only one on-axis AV with a single topological charge along the beam axis, and also provides the feasibility of off-axis particle trapping with multiple AVs in object manipulation.