A team of researchers from the Universities of Bristol and Sussex in collaboration with Ultrahaptics have built the world’s first sonic tractor beam that can lift and move objects using sound waves.
Tractor beams are mysterious rays that can grab and lift objects. The concept has been used by science-fiction writers, and programmes like Star Trek, but has since come to fascinate 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 technique, published in Nature Communications, could be developed for a wide range of applications, for example a sonic production line could transport delicate objects and assemble them, all without physical contact. On the other hand, a miniature version could grip and transport drug capsules or microsurgical instruments through living tissue.
Asier Marzo, PhD student and the lead author, said: “It was an incredible experience the first time we saw the object held in place by the tractor beam. All my hard work has paid off, it’s brilliant.”
Bruce Drinkwater, Professor of Ultrasonics in the University of Bristol’s Department of Mechanical Engineering, added: “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 the University of Sussex and co-founder of Ultrahaptics, explained: “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.”
Holograms are tridimensional light-fields that can be projected from a two-dimensional surface. We have created acoustic holograms with shapes such as tweezers, twisters and cages that exert forces on particles to levitate and manipulate them.
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.
Acoustic Levitation isn’t a new technique
The essence of levitation technology is the countervailing of gravity. It is known that an ultrasound standing wave is capable of suspending small particles at its sound pressure nodes. The acoustic axis of the ultrasound beam in these previous studies was parallel to the gravitational force, and the levitated objects were manipulated along the fixed axis (i.e. one-dimensionally) by controlling the phases or frequencies of bolted Langevin-type transducers.
In the present study, the Ultrasonic Phased Arrays team considered extended acoustic manipulation whereby millimetre-sized particles were levitated and moved three-dimensionally by localised ultrasonic standing waves, which were generated by ultrasonic phased arrays. Their manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its centre is also utilised. The other is the manipulation principle by which a localised standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays. They experimentally confirmed that various materials could be manipulated by our proposed method.
Fabio Evagelista is a Brazilian writer.
Crossed Paths is the first book of the Myra-Hati trilogy, an epic adventure in a post-apocalyptic world, for the lovers of sci-fi / fantasy genre. This is the author’s first work published in America.