It may sound like something from a Star Trek episode, but engineers in Britain have used sound waves to grab and move small objects in what amounts to a "tractor beam."

A team of researchers from the Universities of Bristol and Sussex report they've constructed a working tractor beam that utilizes high-amplitude sound waves to generate an acoustic hologram that can manipulate tiny beads.

Sound waves in a carefully-timed sequence create an area of low pressure that can trap objects, after which they can be manipulated by the waves, the scientists report in the journal Nature Communications.

The principle, the researchers explain, is based on the knowledge that sound waves of alternating high and low pressure can produce a force as they move through a medium such as air.

"We've all experienced the force of sound — if you go to a rock concert, not only do you hear it, but you can sometimes feel your innards being moved," says Bruce Drinkwater, a University of Bristol mechanical engineer. "It's a question of harnessing that force."

In experiments with the system, engineers have been able to hold and then move small pea-shaped polystyrene beads from a distance of 12 to 15 inches away.

Using a grid of small loudspeakers, the engineers created shifting patterns of waves in ultrasound frequencies that could act as tweezers to move tiny objects.

"We all know that sound waves can have a physical effect," Drinkwater says. "But here we have managed to control the sound to a degree never previously achieved."

The sounds are emitted at volume levels between 140 and 150 decibels, which would be ear-shattering for humans; thankfully, at the ultrasound wavelengths of 40 kilohertz, they are above the range of human hearing.

Dogs would not be so lucky, Drinkwater says.

"I think, if you pointed this device at a dog, it would hear it for sure," he notes. "It wouldn't like it; it would run away."

While still just an experimental, proof-of-concept demonstration, there could be many practical applications for such a technology, he says.

"Our method, we hope, will now be applied, both at a smaller scale — maybe for medical purposes — and at a larger scale, potentially for handling dangerous materials in some sort of non-contact production line," he suggests.

In medical use, a miniature version of the tractor beam system could grab and transport drug capsules within the body or manipulate microsurgical instruments through living tissue, he says.

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