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Researchers use high-pitched sound to levitate a sphere

Researchers demonstrate acoustic levitation of a large sphere
There are few things cooler than the way in which scientists are able to get objects to levitate above the ground. But while many of the recent levitating technologies we’ve seen involve electromagnets, a new demonstration carried out by researchers at the University of São Paulo in Brazil and Heriot-Watt University in Edinburgh, Scotland, relies on a different method.

What researchers Marco Andrade, Julio Adamowski, and Anne Bernassau have come up with is a means to levitate a 2-inch solid polystyrene sphere using ultrasonic acoustic waves pitched above the frequency a human can hear.


“The acoustic levitation of small objects is well known among researchers, and it can be achieved by producing an acoustic standing wave between a sound emitter and a reflector,” Andrade told Digital Trends. “If we insert an object much smaller than the wavelength in the acoustic field, there is a phenomenon, called acoustic radiation force, that attracts the small object to a pressure node of the standing wave. Therefore, a small object can be levitated at a pressure node of the standing wave.”

The breakthrough in this new work, however, comes through the generating of an “acoustic standing wave” between the sound emitters and the object. “By doing this, we can levitate objects much larger than the acoustic wavelength,” Andrade continued.

To carry out the ultrasound levitation, the researchers used a setup that relied on three ultrasonic transducers in a tripod formation positioned around the sphere — thereby providing greater 3D stability.

Explaining the advantage of acoustic levitation over magnetic levitation, Andrade said: “Usually, magnetic levitation is applied in the levitation of ferromagnetic materials, which restricts its applications to mainly metallic materials. One of the main advantages of acoustic levitation is that it is material independent. It is possible to levitate a wide range of materials using acoustic levitation, including liquid drops, metallic objects, and other materials.”

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