Cyclones and attractive streaming generated by acoustical vortices

Abstract

Acoustical and optical vortices have attracted large interest due to their ability in capturing and manipulating particles with the use of the radiation pressure. Here we show that acoustical vortices can also induce axial vortical flow reminiscent of cyclones whose topology can be controlled by adjusting the properties of the acoustical beam. In confined geometry, the phase singularity enables generating "attractive streaming" with a flow directed toward the sound source. This opens perspectives for contact-less vortical flow control.

Observation of Orbital Angular Momentum Transfer from Bessel-Shaped Acoustic Vortices to Diphasic Liquid-Microparticle Mixtures

“…(6) in the present paper for a Bessel-shaped field is obtained. region, the rotational rate decreases rapidly with r. These predicted rotational speed distributions are in qualitative agreement with the extended model presented in [25].…”

“…In parallel, the propagation of acoustic helicoidal beams and their interaction with objects has been explored from a theoretical perspective [22][23][24]. In particular Riaud et al [25] described a model based on an extension of Eckart perturbation theory which predicts the above rotational acoustic streaming phenomena due to a Bessel beam. 3 Inspired by optical tweezers, acoustic radiation force (ARF) trapping devices for manipulating microscopic objects have attracted significant attention, particularly for cell manipulation applications [26,27].…”

Observation of a Single-Beam Gradient Force Acoustical Trap for Elastic Particles: Acoustical Tweezers

“…Nevertheless, the particle reaches an axial equilibrium position when the negative radiation force balances adverse effects acting in the direction of propagation and the axial equilibrium position is generally below the beam's focus (typically 30.0 mm away from the lens). These opposite forces are the positive axial scattering force, the gravity and the viscous drag force resulting from the acoustic streaming, that is to say a flow generated by acoustic absorption of the beam's intensity in the bulk of the fluid [40,41]. The only weight of the sphere represents 20 nN for the largest polystyrene particles.…”

Taming the degeneration of Bessel beams at an anisotropic-isotropic interface: Toward three-dimensional control of confined vortical waves

“…This torque can be used to rotate objects [1,9,10] or generate controlled vortical flows [11]. These waves can also be useful for in-depth microscopy since they can self-reconstruct after being damaged by obstacles on the propagation axis [12,13].…”