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Using Sound To Levitate Objects And Move Them Midair

An image shows particles levitating in space between four sets of speakers. A Japanese team says they have used the system to manipulate items in mid-air.
Yoichi Ochiai
An image shows particles levitating in space between four sets of speakers. A Japanese team says they have used the system to manipulate items in mid-air.

Researchers in Tokyo have put a new twist on the use of sound to suspend objects in air. They've used ultrasonic standing waves to trap pieces of wood, metal, and water – and even move them around.

Researchers have used sound to levitate objects in previous experiments, dating back decades. But that work has largely relied on speakers that were set up in a line to bounce sound waves off a hard surface.

The new experiment uses four speakers to surround an open square area that's about 21 inches wide. Four phased arrays use standing waves to create an ultrasonic focal point in that space, as the researchers explain in a video about their work.

That means that they generate a suspending force — which can then trap particles and objects in mid-air. The objects can be moved around by manipulating the waves.

The researchers' video shows several items being placed in the test area, from drops of water to small plastic and metal machine parts and a length of a wooden match measuring three centimeters.

The device uses sound at the frequency of 40 kHz — beyond the upper limits of human hearing at 20 kHz.

The University of Tokyo researchers' video, called Three-Dimensional Mid-Air Acoustic Manipulation [Acoustic Levitation], expands on a research article they submitted to arXiv, a science publishing site maintained by Cornell University, last month.

Here's how the researchers describe their work:

"Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its center is also utilized. The other is the manipulation principle by which a localized standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays."

The Japanese researchers — Yoichi Ochiai, Takayuki Hoshi, and Jun Rekimoto — say they're looking at ways to manipulate larger objects. And it seems they also see their device as a potential option for moving items around in low-gravity environments, such as in space or orbit.

"It has not escaped our notice that our developed method for levitation under gravity suggests the possibility of developing a technology for handling objects under microgravity," they write.

The levitation techniques open another window into a potential future of manipulating devices — earlier today, Mark wrote about an MIT project that created a way to let people move items remotely within a workspace.

We first spotted the eye-catching video of their sound-levitation work at the tech site Hardware 360.

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Bill Chappell is a writer and editor on the News Desk in the heart of NPR's newsroom in Washington, D.C.
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