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Phoenix666 [soylentnews.org] writes:

Using a simple set of loudspeakers, scientists have figured out a way to levitate and rotate objects in midair [sciencemag.org]. If perfected, this “sonic tractor beam” could find uses ranging from treating kidney stones to creating artificial gravity on the International Space Station.

Scientists have used sound to levitate objects before. That feat isn't surprising, as sound is a wave of pressure strong enough to move your eardrum. However, instead of audible sound, sonic levitation utilizes higher ultrasonic frequencies that are beyond the range of human hearing. When blared from loudspeakers in the right configuration, these sound waves can combine to form a sonic scaffolding called an interference pattern—a sort of a force field that can hold a small object aloft.
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The algorithm works by constructing the best possible interference patterns, one that not only keeps the bead floating, but lets it twist and move with some freedom. The interference pattern comes about by adjusting the precise synchronization, or “phases,” of the waves leaving the various speakers. By setting the phase differences just right, the researchers make the waves combine to reinforce one another in some places and cancel out one another in other places. In that way they create a complex 3D pattern of high and low pressure regions, which the authors call an "acoustic hologram," that can support the bead against the pull of gravity. As the algorithm tunes the phases, the interference pattern and resulting hologram change, enabling researchers to move the bead around.

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