Axial acoustic radiation force on rigid oblate and prolate spheroids in Bessel vortex beams of progressive, standing and quasi-standing waves

• Published in: Ultrasonics Vol. 74; pp. 62 - 71
• Main Author: Mitri, F.G.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-02-2017
• Subjects: Acoustic radiation force; Acoustical tweezers; Bessel beam; Partial-wave series expansion (PWSE); Spheroid; Tractor beam; Acoustical tweezers; Spheroid; Tractor beam; Bessel beam; Partial-wave series expansion (PWSE); Acoustic radiation force
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2016.09.022

•The partial-wave series expansion method is used to derive the force on spheroids.•Oblate and prolate spheroids centered on Bessel vortex beams are considered.•The Neumann boundary condition is applied to compute the scattering coefficients.•Single tractor beam and dual-beam acoustical tweezers behaviors are established.•Applications in levitation and particle manipulation benefit from the results.
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. Applications in acoustic levitation, particle manipulation and acousto-fluidics would benefit from the results of the present investigation.