Scientists Use Sound to Make Things Fly

July 16, 2013 | Andy Cush

Before we get into this, it’s helpful to remember how sound works. An object vibrates at a particular frequency, which causes the air molecules around it to vibrate at the same frequency. Those air molecules bump into other air molecules, causing them to vibrate at that same frequency, and so on and so on, until some vibrating molecules reach you ear, where a system of tiny little parts react to that vibration and send information about it to your brain, which interprets the information as sound. This is the process behind the idea that “in space, no one can hear you scream.” If there’s no air, there’s no mechanism to carry sound.

So sound is, at its heart, a bunch of molecules moving around really fast. Got it? Good.

A bunch of researchers in Switzerland who know lots more about sound than you or I built a device that lets them levitate small objects using high-frequency sound that’s inaudible to humans as a physical force. Watch it in action above, and keep reading if you want to find out how it works.

New Scientist explains, and, just as a warning, this gets a little heady, but we’ll explain in a minute.

This has been done previously, by using speakers or other resonators to fire pressure waves upwards and bounce them off a reflector. The original waves and their reflections then combine to create a standing wave, with a series of stationary “nodes” that stay put even as the wave oscillates.

If the standing wave has the right frequency, the force at these nodes exactly cancels gravity – and anything trapped there hovers in place.

Sound waves are ordinarily moving very quickly back and forth at all times, but if, at the right you can combine a wave with its own mirror image–think of this as the echo of a sound coming back at it, basically–you can make it stand still at particular point, or “node.” There’s enough force pushing a molecule up to keep it from falling, and enough pushing it down to keep it from shooting up into the air. Now, put an object at that spot that’s stuck in space, and the forces will act upon it too. And if the wave is powerful–loud–enough, those forces will be strong enough to counteract gravity, and the object will just float there.

If that’s not mind-boggling enough, what makes this team’s device so special is that it can move the objects that it levitates by slowly varying the shapes of the waves it creates. In the video above, they use this property to create the a single drop of coffee by hovering some water and a bit of instant coffee, then jamming them together in the air.

So you’re thinking, “could this levitate a person?” And the answer is “maybe.” As you might imagine, these sounds have to get pretty fucking loud to counteract gravity, especially when asked to lift our fat asses. So loud, in fact, that if you accidentally slipped out of your safe little node, it might kill you.

“I see no problem with [levitating a person],” said Dimos Poulikakos, one of the researchers who developed this particular machine. “Whether a human being could survive the acoustic forces, I’m not 100 per cent sure.”