October 27, 2015

From science fiction to reality -- sonic tractor beam invented

Caption: The research team have created three-dimensional acoustic fields
with shapes such as fingers, twisters and cages. These acoustic fields are the
first acoustic holograms that can exert forces on particles to levitate and
manipulate them. Credit: Image courtesy of Asier Marzo, Bruce Drinkwater
and Sriram Subramanian © 2015

(October 27, 2015)  The world’s first sonic tractor beams that can lift and move objects using soundwaves have been built by a team that includes researchers at the University of Sussex.

Tractor beams are mysterious rays that can grab and lift objects. The concept was created by science-fiction writers  but has since come to fascinate scientists and engineers.

Researchers at the Universities of Sussex and Bristol, in collaboration with Ultrahaptics, have now built a working tractor beam that uses high-amplitude sound waves to generate an acoustic hologram that can pick up and move small objects.

Asier Marzo, PHD student and lead author,
levitating a polystyrene ball with soundwaves.

The technique, published in Nature Communications today (27 October 2015), could be developed for a wide range of applications. For example, a sonic production line could transport delicate objects and assemble them, all without physical contact. Or a miniature version could grip and transport drug capsules or microsurgical instruments through living tissue.

Caption: Holograms are tridimensional light-fields that can be projected from a two-dimensional
surface. The researchers have created acoustic holograms with shapes such as tweezers,
twisters and cages that exert forces on particles to levitate and manipulate them.
Credit: Image courtesy of Asier Marzo, Bruce Drinkwater and Sriram Subramanian © 2015

Sriram Subramanian, Professor of Informatics at the University of Sussex and co-founder of Ultrahaptics, explained: "In our device we manipulate objects in mid-air and seemingly defy gravity. We can individually control dozens of loudspeakers to tell us an optimal solution to generate an acoustic hologram that can manipulate multiple objects in real-time without contact.”

The researchers used an array of 64 miniature loudspeakers (driven at 40Khz with 15Vpp. The whole system consumes 9 Watts of power) to create high-pitched and high-intensity sound waves to levitate a spherical bead (of up to 4mm in diameter) made of expanded polystyrene.

The tractor beam works by surrounding the object with high-intensity sound to create a force field that keeps the objects in place. By carefully controlling the output of the loudspeakers, the object can be either held in place, moved or rotated.

Asier Marzo, PhD student and the lead author, said: "It was an incredible experience the first time we saw the object held in place by the tractor beam. All my hard work has paid off. It's brilliant."

Bruce Drinkwater, Professor of Ultrasonics in the University of Bristol's Department of Mechanical Engineering, added: "We all know that sound waves can have a physical effect. But here we have managed to control the sound to a degree never previously achieved."

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journal reference (Open Access) >>