Whoa: Watch Scientists Use Sound Waves to Make Things Levitate | Wired Design | Wired.com: ...scientists have been experimenting with acoustic levitation for decades, using sound waves to suspend materials in mid-air. What’s new here, though, is the ability to move those materials in three dimensions.
That’s made possible by the unique arrangement of the speakers themselves. Where former setups bounced sound waves off a solid plate, the Tokyo researchers instead use four panels of speakers, all facing each other. These walls combine to create an “ultrasonic focal point,” which can be moved—along with the object trapped in it—by adjusting the output from each speaker array.