European Researchers Create Acoustic Tractor Beam �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 brilliant,� said Asier Marzo of the University of Bristol and the Public University of Navarre, a team member and the first author of a paper in the journal Nature Communications.

The tractor beam crated by Marzo and his colleagues uses high-amplitude sound waves to generate an acoustic hologram which can pick up and move small objects.

�We all know that sound waves can have a physical effect,� explained co-author Prof. Bruce Drinkwater of the University of Bristol.

�But here we have managed to control the sound to a degree never previously achieved.�

�In our device we manipulate objects in mid-air and seemingly defy gravity. Here we 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,� added co-author Prof Sriram Subramanian of the University of Sussex and Ultrahaptics Ltd.

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

The tractor beam works by surrounding the object with high-intensity sound and this creates 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.

The researchers 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 stuck-in and then 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.

�The technique 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,� the scientists said.

�On the other hand, a miniature version could grip and transport drug capsules or microsurgical instruments through living tissue.�

Marzo and co-authors are now designing different variations of their system: a bigger version with a different working principle that aims at levitating a soccer ball from 33 feet (10 m) away; and a smaller version, targeted at manipulating particles inside the human body.