共轴双涡旋声束形成离轴多涡旋的定位

涡旋声束具有螺旋的相位波前,中轴线上形成声强为零的相位奇点,其所携带的轨道角动量在粒子操控领域有着广阔的应用前景。传统声涡旋只在传播轴线上形成一个拓扑荷可控的涡旋波束,这限制了声涡旋的应用灵活性。基于环形点声源阵列和相位编码技术,利用奇偶声源分别产生共轴双涡旋声束的声场叠加,在传播截面上形成了具有中心涡旋和子涡旋的离轴多涡旋声场;研究了双涡旋拓扑参数对离轴涡旋的个数、位置及拓扑荷的影响,基于声涡旋的径向声压和相位分布,确定了离轴涡旋的离轴半径,并结合声源位置推导子涡旋中心方位角的计算公式,实现离轴涡旋的精确定位。本研究突破了沿轴分布的涡旋声场只能形成单点涡旋势阱的操控局限,为利用离轴多涡旋实现多点粒子捕获提供了理论依据,促进涡旋声场在精确粒子操控和传输方面的高效应用。 

Localization of off-axis multiple acoustic vortices formed by two coaxial vortex beams

Acoustic Vortex (AV) is a special acoustic field with a helical wave front and a pressure-zero phase singularity at the center.The Orbit Angular Momentum (OAM) carried by an AV beam can be transferred to objects,exhibiting good application potential in particle manipulation.Whereas,only an AV beam with controllable topological charges can be formed along the center transmission axis,which limits the flexibility in practical applications.Based on the circular array of point sources and the phase-coded approach,two coaxial AV beams with different topological charges are generated by the even and odd numbered sources at a same frequency,and several off-axis multiple AVs are formed on a circumference.Based on the radial distributions of pressure and phase,the number and the topological charge of the generated off-axis multiple AVs are analyzed with an accurate radius between the vortex center and the center axis,and the accurate azimuthal angles of AVs are derived based on the spatial angle difference of the sources.The generation of off-axis AVs overcomes the limit of only one center vortex trap along the center axis of the traditional AV technology.The favorable results provide the basis for off-axis multi-point trapping and open a new area of effective precise particle manipulation in biomedical engineering.