Science & Technology

# We Can Make Things Levitate Using Sound

Nothing says "the future" like levitation. From Marty McFly's hoverboard to the landspeeders of Star Wars, levitating tech is enough to get any nerd excited. And we're getting closer to making it a reality every day. We can already make tiny things float in mid-air thanks to acoustic levitation, and we may soon be able to do the same with large objects.

## The Sound of Science

There are actually a few different ways that we can levitate objects. Magnetic levitation works great as long as you're trying to levitate something, you know, magnetic. Quantum levitation is mind-blowing, but implementing it is a few years off. Our best bet is probably acoustic levitation, which uses sound waves to suspend objects and materials in mid-air. There's just one problem: It only works on objects that are smaller than the sound waves themselves. That means you can float all of the ants that you want, but it won't work if you want to pull off something like this:

#### Floating Bonsai Trees

Acoustic levitation works by creating tiny pockets in space where sound waves resonate with each other to create a standing wave. A standing wave has certain points, called "nodes," that stay still while the rest of the wave oscillates. Think of a node like a hapless music fan trying to leave a concert: As everyone else moves in different directions around him, they all push on him with equal force so that he never goes anywhere. In a standing wave, you have the same amount of energy coming from opposite directions so that the nodes don't move anywhere. You've got to be able to rest an object on one of these nodes if you're going to levitate it — and for that reason, scientists have believed that it literally could not be done if the object was bigger than the wave. But a new report suggests that bigger floaters could be in our future.

## Bigger Fish to Float

Instead of creating a solid standing wave between two sound waves coming from opposite directions, the new method rotates sound waves in opposite directions, creating tornado-like structures of sound known as acoustic vortices. In the center of the vortices — the eye of the tornado, if you will — is where the objects can be held. Researchers have already proven larger-scale levitation is possible: They've floated a 2-centimeter sphere made of synthetic polymer. Thrilling!

Okay, so that's more proof-of-concept than anything else. But it proves that it's at least theoretically possible to levitate large objects, and maybe even people. Supervisor Bruce Drinkwater thinks that a more practical application is much closer at hand. In a press release, he says "I'm particularly excited by the idea of contactless production lines where delicate objects are assembled without touching them." Sounds cool, Bruce, but we're still holding out for hoverboards.

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Magnetic levitation, or maglev, is the kind of levitation you're probably most familiar with. Find out how it works in "Rising Force: The Magic of Magnetic Levitation" by James D. Livingston. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Reuben Westmaas