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A concept that admittedly conjures up notions of science fiction, the tractor beam has been used in countless stories as a beam of light that can pull objects into its clutches. Thanks to a group of scientists and researchers at the University of Bristol, a tractor beam is no longer just sci-fi lore – a team led by Bruce Drinkwater, Professor of Ultrasonics, has developed a functional tractor beam that uses powerful sound waves to levitate, rotate and move millimeter-sized objects.

Light has always been the go-to method for creating a tractor beam, and numerous other scientists have managed to harness light in the form of strong laser beams due to its ability to create momentum and transfer that force to other objects. However, these attempts only ever managed to move microscopic sized objects, and required a great amount of power to do so. Drinkwater’s team decided to turn to sound vibrations, and fared much better, though their original intent wasn’t to produce a tractor beam at all.

Drinkwater and his colleagues were already working with small loudspeakers to develop technology that would create “a sense of touch in mid-air using waves.” By playing around with the phase of the speakers, they created a powerful, focused acoustic pressure as a means of forming a new brand of human-computer interactivity. Realizing that they had the equipment and theoretical science in place to conceivably create a sonic tractor beam, Drinkwater and his colleagues set out to do what any scientist worth their salt would do: experiment.

Using a computer system to run simulations, Drinkwater and his team discovered that stable levitation was at the core of any feasible tractor beam. They worked to ensure that they could establish acoustic pressure that managed to be both low enough but surrounded with high-intensity sound imperceptible to human ears that could converge and latch onto an object. They finally managed to pinpoint the exact amplitude and phase of their loudspeakers that produced a gripping, tractor beam effect that suspended particles against gravity.

The magenta represents area where particles can be manipulated in a controlled manner using sound waves.

So far, Drinkwater’s technique only works for objects that are a mere millimeter in size due to the fact that the objects need to be smaller than the wavelength of surrounding sound waves in order to be lifted. Theoretically, larger objects could be lifted with lower sound frequencies, but at the expense of some very loud, audible sound waves.

Already, Drinkwater has conceived of ways this sonic tractor beam could be put to effective use, including handling volatile or sensitive materials such as explosives and chemicals. There are also potential applications where an array of trapped objects in a tractor beam could form 3D displays, or be deployed within the human body to better target and deliver drugs and perform small-scale medical procedures. Interestingly, the use of tractor beams in space, as is oft depicted in science fiction, isn’t as sound of a concept. Acoustic waves can’t travel through the vacuum of space, so Drinkwater’s sonic tractor beam won’t be equipped on any spacecrafts anytime soon. Nevertheless, there is a wealth of possibilities to be cultivated from this staggeringly cool breakthrough.

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