Last year, researchers at the University of Dundee revealed an acoustic tractor beam that used ultrasonic energy to pull macroscopic objects in. Now researchers in the UK have developed a sonic tractor beam that generates acoustic holograms through the manipulation of high-amplitude sound waves. These acoustic holograms, which can take various shapes, such as fingers, cages and vortexes, are able to pick up and move small objects like polystyrene beads.

Researchers at the Universities of Bristol and Sussex, working in collaboration with Bristol-based Ultrahaptics, created a system that uses an array of 64 tiny loudspeakers to generate high-pitched, high-intensity sound waves. These sound waves act as a sort of force field to hold an object in place. It then becomes possible to move or rotate the objects by controlling the output of the loudspeakers.

"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," says Sriram Subramanian, Professor of Informatics at the University of Sussex and co-founder of Ultrahaptics.

The team generated three types of acoustic holograms or force fields capable of acting as tractor beams. One force field with the shape of an acoustic twister-like vortex is capable of trapping things at its core. Another shaped like a high-intensity sound-cage surrounds an object and holds it in place from every direction. The third forms something akin to a pair of tweezers or fingers.

Possible applications for the technology include tiny sonic tractor beams that could be used to ferry drugs or microsurgical instruments through tissues in the body. It's also possible, the team says, to have sonic production lines that levitate, transport and assemble delicate components without any human interference.

The researchers are now working on creating a bigger and more powerful version of the sonic tractor beam, that will be capable of levitating a soccer ball at a distance of 10 m (32 ft). They also plan to develop a smaller model that can manipulate particles within the human body. Their research was recently published in the journal Nature.

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