前进波、驻波和准驻波贝塞尔涡旋束中刚性扁球体和长球体上的轴向声辐射力
Axial acoustic radiation force on rigid oblate and prolate spheroids in Bessel vortex beams of progressive, standing and quasi-standing waves
摘要：
将球坐标系下的分波级数展开（PWSE）方法推广到求解分别由行波、驻波和准驻波组成的高阶Bessel涡束的波传播轴上的刚性扁球和长椭球所受的声辐射力。应用Neumann边界条件，在非粘性流体中的不可移动的表面后，导出耦合的线性方程组，并在执行单个数值积分程序后通过矩阵求逆来数值求解。线性方程组的系统依赖于分波指数n和贝塞尔涡旋光束m的阶数，使用截断但收敛的PWSE在最小二乘意义上。计算了辐射力函数的数值结果，辐射力函数是单位能量密度和单位横截面积的辐射力，特别强调了描述从前进波到纯驻波情况的过渡的振幅比，纵横比（即，椭球体的长轴与短轴之比）、贝塞尔涡旋光束的半锥角和阶数以及无量纲尺寸参数。本文导出了贝塞尔涡旋光束的行波、驻波和准驻波辐射力函数的一般表达式。通过适当选择光束参数，该表达式可以推广到其他类型的光束/波，如零阶贝塞尔无涡旋光束或无限平面波。前进波的结果揭示了牵引光束的行为，其特征在于出现了一个有吸引力的拉力作用在波传播的相反方向。此外，双光束贝塞尔涡旋光束在准驻波和纯驻波情况下的转变显示了声镊特性。
英文摘要：
The analysis using the partial-wave series expansion (PWSE) method in spherical coordinates is extended to evaluate the acoustic radiation force experienced by rigid oblate and prolate spheroids centered on the axis of wave propagation of high-order Bessel vortex beams composed of progressive, standing and quasi-standing waves, respectively. A coupled system of linear equations is derived after applying the Neumann boundary condition for an immovable surface in a non-viscous fluid, and solved numerically by matrix inversion after performing a single numerical integration procedure. The system of linear equations depends on the partial-wave index n and the order of the Bessel vortex beam m using truncated but converging PWSEs in the least-squares sense. Numerical results for the radiation force function, which is the radiation force per unit energy density and unit cross-sectional surface, are computed with particular emphasis on the amplitude ratio describing the transition from the progressive to the pure standing waves cases, the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid), the half-cone angle and order of the Bessel vortex beam, as well as the dimensionless size parameter. A generalized expression for the radiation force function is derived for cases encompassing the progressive, standing and quasi-standing waves of Bessel vortex beams. This expression can be reduced to other types of beams/waves such as the zeroth-order Bessel non-vortex beam or the infinite plane wave case by appropriate selection of the beam parameters. The results for progressive waves reveal a tractor beam behavior, characterized by the emergence of an attractive pulling force acting in opposite direction of wave propagation. Moreover, the transition to the quasi-standing and pure standing wave cases shows the acoustical tweezers behavior in dual-beam Bessel vortex beams.
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