Asier Marzo, PHD student, levitating a polystyrene ball with sound waves.
Tractor beams are mysterious rays that can grab and lift objects. Now, researchers have built a working tractor beam that uses high-amplitude sound waves to generate an acoustic hologram that can pick up and move small objects.

The researchers used an array of 64 miniature loudspeakers to create high-pitched and high-intensity sound waves to levitate a spherical bead (of up to 4 mm 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 held in place, moved, or rotated.

A bigger version with a different working principle aims at levitating a soccer ball from 10 meters away, and a smaller version is targeted at manipulating particles inside the human body.

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