This Sound levitation technology could be used for medicine and surgical manipulation of body tissues

The tractor beam, one of science fiction’s most iconic devices, is one step closer to reality, scientists from the Universities of Bristol and Sussex announced recently in a paper published in the journal Nature Communications.

But while the ability to move entire spaceships without touching them may still be far off, immediate applications of the new technology include the ability to manipulate tiny surgical instruments from outside of a patient’s body.

“What we’ve got is a fully working tractor beam,” said co-lead author Bruce Drinkwater. “We can grab objects, we can twist them, we can rotate them, we can move them. Previously people knew that these forces were present, but it’s another thing to harness them in a stable way.”

Levitating objects is now a reality

Previous research had shown that objects could theoretically be moved using only light or sound waves. In fact, tractor beams have previously been constructed using high-powered lasers, but these devices are only able to move very tiny objects.

Then last year, researchers from the University of Dundee used sound to build a tractor beam capable of moving larger objects — but that device could only function for very short periods of time.

The new study is the first time that researchers have been able to hold up and manipulate objects in mid-air with sound waves alone. They surrounded a 4 mm-wide polystyrene ball with 64 miniature loudspeakers, then used the speakers to create a three-dimensional “acoustic hologram.” The energy from these sound waves was sufficient to levitate the ball.

Notably, the researchers were then able to adjust the frequency of sound from the individual speakers the change the shape of the acoustic “force field” manipulating the ball. They were able to create fields in the shape of a cage enclosing the ball, a swirling vortex rotating it, or a pair of tweezers or fingers moving it around.

“Unprecedented acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation,” the researchers wrote.

There is no theoretical obstacle to using the device to levitate living things.

“It’s hard to get across just how weird it is to see things levitating in space, when you can’t see or hear anything,” Drinkwater said. “One minute it didn’t work, and the experiments were the most disappointing you could ever imagine, with little things firing off in the wrong direction – and then suddenly there they were, levitating before your eyes.”

“It was an incredible experience the first time we saw the object held in place by the tractor beam,” agreed co-lead author Azier Marzo. “Finally, after months of beads being spitted uncontrollably from the tractor beam we had success. All my hard work has paid off, it’s brilliant.”

Soon ready for medical applications?

Currently, the device cannot levitate an object any larger than the ball used in the study. Marzo said that such devices — “more powerful tractor beams capable of levitating bigger objects from farther distances” — could be used, for example, to allow astronauts to manipulate external objects from within the safety of a space capsule.

Although scientists are working to scale up the device’s power, this would probably require using very loud sound waves within the human range of hearing.

Even as-is, however, the device has astonishing potential uses.

“Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically-controlled micro-machines that do not interfere with magnetic resonance imaging (MRI),” the researchers wrote.

Other medical uses could involve the non-surgical removal of obstructions such as kidney stones or blood clots, or the manipulation of tiny surgical instruments.

“Sound waves can travel through water and human tissue – that is how ultrasound imaging works,” Marzo said. “Our objective is neither to destroy nor to image, but to manipulate things inside our body.”