We May Soon Be Levitating Humans Thanks to This Acoustic Tractor Beam Breakthrough
Right now, there's only three ways to "levitate," each of which is on a sliding spectrum of fun: get one of those wingsuits and jump in a wind tunnel, buy a ticket on a Vomit Comet (which simulate zero-g for passengers by losing altitude for a few minutes), or wrap yourself in magnets and suspend yourself a few centimeters above a plate of metal. That's about as far as modern science has brought us...until today.
Yesterday, scientists at the University of Bristol published a paper in Physical Review Letters that explains how they managed to use an acoustic vortex (essentially an invisible tornado composed of ultrasonic waves at a pitch of 40kHz) to levitate a small polystyrene ball. Scientists have been using "acoustic tractor beams" to levitate small objects for a while, but what makes this experiment groundbreaking is that it broke through a threshold previously thought impossible, opening a door to vortexes that can levitate much, much larger objects.
Previously, it was thought that acoustic vortexes could only lift objects that were the same size (or smaller) than the wavelengths of the sound waves themselves:
"Researchers previously thought that acoustic tractor beams were fundamentally limited to levitating small objects as all the previous attempts to trap particles larger than the wavelength had been unstable, with objects spinning uncontrollably. This is because rotating sound field transfers some of its spinning motion to the objects causing them to orbit faster and faster until they are ejected."
However, reversing the direction of the acoustic waves (which create spirals just like a tornado) rapidly meant that researchers could stabilize the object and keep it from spinning out of control. It also meant they could enlarge the silent core of the vortex, where the object sits. Being able to hold larger objects in this silent core is the key to all kinds of potential advancements, including manipulating extremely delicate objects without touching them. This could be applied to everything from assembly lines to surgical tools, say researchers.
According to Dr. Mihai Caleap, a senior researcher on the project: "In the future, with more acoustic power it will be possible to hold even larger objects. This was only thought to be possible using lower pitches making the experiment audible and dangerous for humans."
With higher pitches and more powerful vortexes, acoustic levitation for humans may be within reach. Until then, we'll have to keep trundling along sadly on our fake "hoverboards."