Tractor beam lifts and moves small objects

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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 technique, developed by researchers from the Universities of Bristol and Sussex in collaboration with Ultrahaptics, could be developed for a wide range of applications, including a sonic production line to transport and assemble delicate objects without physical contact.

Similarly, it is claimed that a miniature version could grip and transport drug capsules or microsurgical instruments through living tissue.

Holograms are tridimensional light-fields that can be projected from a two-dimensional surface. The researchers have created acoustic holograms with shapes such as tweezers, twisters and cages that exert forces on particles to levitate and manipulate them
Holograms are tridimensional light-fields that can be projected from a two-dimensional surface. The researchers have created acoustic holograms with shapes such as tweezers, twisters and cages that exert forces on particles to levitate and manipulate them

Bruce Drinkwater, Professor of Ultrasonics in Bristol University’s Department of Mechanical Engineering, said: “We all know that sound waves can have a physical effect. But here we have managed to control the sound to a degree never previously achieved.”

Sriram Subramanian, Professor of Informatics at Sussex University and co-founder of Ultrahaptics, added: “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.”

The researchers used an array of 64 miniature loudspeakers to create high-pitch and high-intensity sound waves. The tractor beam is said to work 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 held in place, moved or rotated.

The team has shown that three different shapes of acoustic force fields work as tractor beams.  The first is an acoustic force field that resembles a pair or tweezers.  The second is an acoustic vortex, the objects becoming stuck-in and then trapped at the core. Bristol University said that the third could be described as a high-intensity cage that surrounds the objects and holds them in place from all directions.

A paper - Holographic acoustic elements for manipulation of levitated objects by Asier Marzo, Sue Ann Seah, Bruce W. Drinkwater, Deepak Ranjan Sahoo, Benjamin Long and Sriram Subramanian - is published in Nature Communications.