Ultrasonic Sound tornadoes levitate objects in a soundless void

Researchers at the University of Bristol have been able to levitate objects using ultrasonic waves larger than the wavelengths of sound used by the device.

This could enable touchless control of drug capsules or micro-surgical implements inside the human body using sound.

Above – A styrofoam particle of 1.6cm (1.88 wavelengths of sound) trapped in the center of a “tornado” of ultrasonic waves. University of Bristol

This could enable production lines where delicate objects are assembled without any physical contact.

Sound tornadoes are created and a soundless void holds the objects.

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 (so called Mie particles).

Physical Review Letters – Acoustic virtual vortices with tunable orbital angular momentum for trapping of Mie particles

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