A team of researchers have built the world's first sonic tractor beam that can lift and move objects using sound waves. Tractor beams can grab and lift objects, a concept that has been used by science-fiction writers and has since fascinated scientists and engineers.

Researchers have now built a working tractor beam that uses high-amplitude sound waves to generate an acoustic hologram which can pick up and move small objects. 

The researchers used an array of 64 miniature loudspeakers to create high-pitch and high-intensity sound waves. 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 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 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 research team has created three-dimensional acoustic fields with shapes such as fingers, twisters and cages. These acoustic fields are the first acoustic holograms that can exert forces on particles to levitate and manipulate them. Image courtesy of Asier Marzo, Bruce Drinkwater and Sriram Subramanian © 2015

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.