The kids at Hogwarts may have been able to make feathers float by shouting out "Wingardium Leviosa!" But researchers at the University of Tokyo have found a different way to levitate objects with sound.
Yoichi Ochiai and his colleagues use ultrasound, sound waves that are outside the human hearing range. Their findings are published on the database arXiv.
Chris Benmore, senior physicist at the Argonne National Laboratory near Chicago, said that the technique relies on some basic principles of physics. "When you step in front of a speaker, you can feel the pressure of the sound," he told ABC News. "But when you have two speakers facing each other, there are regions where it's twice as loud and regions where they cancel out. In the areas where it's canceled is a little void."
Those voids, also known as nodes, act as little pockets that can support a small object. "It's kept in there by the pressure of the wave," said Benmore. "The thing that this team did differently is using four speaker arrays that can move the object in three dimensions."
But don't expect to master the art of levitation with a fancy stereo system. The wavelength of the sound plays a role in how big of an object can be hoisted up into the air. "The [researcher's] setup isn't going to levitate a person or even a goldfish," said Benmore. "It's limited to objects about 2 millimeters in size."
While it makes for a neat parlor trick, Benmore adds that there are practical uses for acoustic levitation. "I use it to make amorphous drugs," he said. Amorphous drugs can be ten to a hundred times more potent than their crystal form, making them easier to be taken up by the body. "Acoustic levitation is a very useful application in making fast-acting drugs."
The researchers acknowledge another potential for their speaker setup, although it's literally out of this world. "It has not escaped our notice that our developed method for levitation ... suggests the possibility of developing a technology for handling objects under microgravity," they write.