Researchers at the Universities of Sussex and Bristol, in collaboration with Ultrahaptics, have now built a working tractor beam that uses high-amplitude soundwaves to generate an acoustic hologram that can pick up and move small objects.
The team is now designing different variations of this system. A bigger version with a different working principle that aims at levitating a soccer ball from 10 meters away; and a smaller version, targeted at manipulating particles inside the human body.
It 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.
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.
Pictures of one-sided levitation in mid-air
Nature Communications - Holographic acoustic elements for manipulation of levitated objects
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 soundwaves can have a physical effect. But here we have managed to control the sound to a degree never previously achieved."
The team have shown that three different shapes of acoustic force fields work as tractor beams. The first is an acoustic force field that resembles a pair of fingers or tweezers. The second is an acoustic vortex, the objects becoming trapped at the core and the third is best described as a high-intensity cage that surrounds the objects and holds them in place from all directions.
Previous work on acoustic studies had to surround the object with loudspeakers, which limits the extent of movement and restricts many applications. Last year, the University of Dundee presented the concept of a tractor beam but no objects were held in the ray.