Negative pulling acoustic radiation force on spheroids in Bessel vortex beams

Abstract

The emergence of a negative pulling acoustic radiation force on rigid spheroids is examined, with the use of acoustical Bessel vortex (helicoidal) “tractor” beams. Numerical predictions based on the acoustical scattering phenomenon [F. G. Mitri, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 62, 1809-1818 (2015); Ann. Phys. (NY) 363, 262-274 (2015)] that is extended to calculate the longitudinal acoustic radiation force (i.e., acting along the direction of wave propagation) illustrate the theory, with particular emphasis on the aspect ratio of the spheroid, the half-cone angle and order of the beam, as well as the dimensionless frequency parameter. It is shown that the Bessel vortex beam composed of progressive (i.e., traveling) waves is capable of generating a negative pulling force acting in opposite direction of the forward linear momentum density flux associated with the incident waves [F. G. Mitri, Europhys. Lett. 112, 34002 (2015)]. The scope of the analysis is further expanded to include the cases of standing and quasi-standing Bessel beam tweezers [F. G. Mitri, Wave Motion 57, 231-238 (2015)]. The results potentially suggest the use of Bessel “tractor” vortex beams for pulling, propelling, or manipulating arbitrary-shaped objects deviating from the spherical geometry for applications in remote sampling, particle manipulation, and handling, to name a few areas.