Tractor beams, the stuff of campy alien invasion films, are nothing new in the real world. You can 3D-print your own small version, but it’s unlikely we’ll see one levitating a whole human anytime soon. However, with a novel approach to how acoustic beams work, doctors could soon use them to manipulate drug capsules throughout your body or remove floaters from your eyes.
Using these techniques in patients is still a long ways off. But a new study out of the University of Bristol in the UK, published in Physical Review Letters on Monday, suggests it can be done. The researchers outline a novel method for levitating objects with sound. A press release calls them “rapidly fluctuating acoustic vortices,” similar to “tornadoes of sound,” where a loud sound surrounds a silent core. An object can levitate in the center.
Using sound at an ultrasonic pitch the human ear can’t detect, the researchers were able to levitate a two-centimetre polystyrene sphere using this method. Doesn’t sound like much, but it’s the most anyone’s made float so far.
“For me, the excitement comes from going beyond what was thought to be a fundamental limit of acoustic trapping,” lead researcher and University of Bristol computer scientist Asier Marzo told me in an email. “Previously, no matter how much power you were using, the trapped particles could never be larger than the wavelength. It is not about absolute sizes but about the relative size of the particle compared to the wavelength.”
In theory, this makes it scalable to larger objects, or smaller ones—like microsurgical implements. Now that scientists can trap particles in a beam that are larger than the wavelength, they’ll be able to manipulate particles using the same frequency. “This would allow doctors to integrate imaging and manipulation in the same ultrasonic machine for instance to locate and move kidney stones or eye floaters,” Marzo said.