https://www.wired.com/story/how-to-levitate-objects-with-sound/

Along with personal jetpacks for every man, woman, and child (sure, why not), levitation is one of those conveniences that sci-fi has long promised us but has yet to deliver, other than magnetically levitating trains. But at Argonne National Laboratory in Illinois, physicist Chris Benmore and his colleagues are levitating objects with an unlikely tool: sound. It's called acoustic levitation, and after breaking your brain with what seems to be an optical illusion, it's poised to deliver advances in pharmacology, chemistry more broadly, and even robotics.

It works like so: Two horns vibrate at 22,000 times a second, firing sound waves into a pocket of air in between the two devices. "When these two waves interact, you'll get what's called a standing wave, so they'll cancel in places and they'll reinforce in others to create nodes and antinodes," says Benmore, of the Lab's Advanced Photon Source facility. "Those particular places where they cancel, you put an object in, and you can levitate it." These vertically arranged pockets cancel the pull of gravity, so Benmore can add tiny balls to the air between the two horns to form a levitating string, or even spray water and watch the fluid coalesce into droplets in the pockets.