Applied Physics

An attractive-sounding proposition

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Science  23 May 2014:
Vol. 344, Issue 6186, pp. 869
DOI: 10.1126/science.344.6186.869-f

Map of the distribution of pressures within the field produced by the ultrasonic tractor beam.

PHOTO: MIKE MACDONALD AND CHRISTINE DEMORE

Demore et al. are using sound to build a better tweezer—or at least, to show how it could be done. Today's optical and acoustic tweezers typically use intensity gradients to trap and manipulate the particles. That's because propagating fields such as light and sound are usually associated with positive forces—the radiation pressure they create tends to push objects away. In contrast, Demore et al. have figured out how to use sound not just to push, but to pull. They use an array of ultrasonic resonators to show how the wavefront of a propagating beam of sound can be shaped to apply negative radiation pressure, creating a tractor beam. The new technology could give surgeons and astronauts greater dexterity as they perform operations and repairs from a distance.

Phys. Rev. Lett. 112, 174302 (2014).

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