Abstract
Acoustic vortices can transfer angular momentum and trap particles. Here, we show that particles trapped in airborne acoustic vortices orbit at high speeds, leading to dynamic instability and ejection. We demonstrate stable trapping inside acoustic vortices by generating sequences of short-pulsed vortices of equal helicity but opposite chirality. This produces a "virtual vortex" with an orbital angular momentum that can be tuned independently of the trapping force. We use this method to adjust the rotational speed of particles inside a vortex beam and, for the first time, create three-dimensional acoustics traps for particles of wavelength order (i.e., Mie particles).
Highlights
Acoustic vortices can transfer angular momentum and trap particles
Acoustic vortices have been extensively studied for their ability to trap particles [1,2,3] and transfer orbital angular momentum (OAM) [4,5,6,7,8,9,10,11,12,13]
Both the trapping force and the OAM are proportional to the total power of the beam [10,11,12], meaning that the rotational speed cannot be controlled independently of the trapping force
Summary
Acoustic Virtual Vortices with Tunable Orbital Angular Momentum for Trapping of Mie Particles. We demonstrate stable trapping inside acoustic vortices by generating sequences of short-pulsed vortices of equal helicity but opposite chirality. This produces a “virtual vortex” with an orbital angular momentum that can be tuned independently of the trapping force. We use this method to adjust the rotational speed of particles inside a vortex beam and, for the first time, create three-dimensional acoustics traps for particles of wavelength order (i.e., Mie particles). A virtual vortex of large aperture (i.e., high helicity) is shown to steadily trap particles with diameters
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