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Researchers develop a simpler approach to acoustic levitation

06 January 2015

A team of Brazilian researchers has developed a new levitation device that can hover a tiny object with more control than any other instrument of its type.

Levitation of expanded polystyrene particles (left) and the simulated standing wave pattern (right). Images courtesy of M. Andrade/University of São Paulo

The device, developed by researchers at the University of São Paulo in Brazil, can levitate polystyrene particles by reflecting sound waves from a source placed above a concave reflector. Changing the orientation of the reflector allow the hovering particle to be moved correspondingly.

Other researchers have built similar devices in the past, but they always required a precise set-up where the sound source and reflector were at fixed 'resonant' distances. This made controlling the levitating objects difficult. The new device shows that it is possible to build a 'non-resonant' levitation device, one that does not require a fixed separation distance between the source and the reflector.

This breakthrough may be an important step toward building larger devices that could be used to handle hazardous materials, chemically-sensitive materials like pharmaceuticals, or even to provide technology for a new generation of high-tech children's toys.

"Modern factories have hundreds of robots to move parts from one place to another," says lead researcher, Marco Aurélio Brizzotti Andrade. "Why not try to do the same without touching the parts to be transported?"

The device Andrade and his colleagues devised was only able to levitate light particles (in this case, polystyrene beads about 3mm across). The next step will be to improve the device to levitate heavier materials.

The first successful acoustical levitators could successfully trap small particles in a fixed position, but new advances have allowed researchers not only to trap, but also to transport particles through short distances in space.

Hitherto, the distance between the sound emitter and the reflector had to be carefully calibrated to achieve resonance before any levitation could occur. This meant that the separation distance had to be equal to a multiple of the half-wavelength of the sound waves. If this separation distance were changed even slightly, the standing wave pattern would be destroyed and the levitation would be lost.

The new levitation device developed by Andrade and his colleagues does not require such a precise separation before operation. According to the researchers, the distance between the sound emitter and the reflector can be continually changed in mid-flight without any effect on levitation performance.

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