Researchers build acoustic tractor beam

Researchers Build Acoustic Tractor Beam

Published 5/8/14

by Bob Yirka

(a) Nonconservative pushing force exerted on an object by a plane wave as a result of strong backscattering. (b) Decreasing of the pushing force due to an enhanced forward scattering in a nonparaxial beam. (c) The authors used a target designed to maximize the forward scattering of acoustic radiation, leading to a pulling nonconservative force towards the source: an acoustic tractor beam. Credit: APS/Alan Stonebraker

ABSTRACT
Negative radiation forces act opposite to the direction of propagation, or net momentum, of a beam but have previously been challenging to definitively demonstrate. We report an experimental acoustic tractor beam generated by an ultrasonic array operating on macroscopic targets (>1  cm) to demonstrate the negative radiation forces and to map out regimes over which they dominate, which we compare to simulations. The result and the geometrically simple configuration show that the effect is due to nonconservative forces, produced by redirection of a momentum flux from the angled sides of a target and not by conservative forces from a potential energy gradient. Use of a simple acoustic setup provides an easily understood illustration of the negative radiation pressure concept for tractor beams and demonstrates continuous attraction towards the source, against a net momentum flux in the system.

Read more at: http://phys.org/news/2014-05-acoustic-tractor.html#jCp

Read more at: http://phys.org/news/2014-05-acoustic-tractor.html#jCp

More information: Acoustic Tractor Beam, Phys. Rev. Lett. 112, 174302 – Published 30 April 2014. dx.doi.org/10.1103/PhysRevLett.112.174302

ABSTRACT
Negative radiation forces act opposite to the direction of propagation, or net momentum, of a beam but have previously been challenging to definitively demonstrate. We report an experimental acoustic tractor beam generated by an ultrasonic array operating on macroscopic targets (>1  cm) to demonstrate the negative radiation forces and to map out regimes over which they dominate, which we compare to simulations. The result and the geometrically simple configuration show that the effect is due to nonconservative forces, produced by redirection of a momentum flux from the angled sides of a target and not by conservative forces from a potential energy gradient. Use of a simple acoustic setup provides an easily understood illustration of the negative radiation pressure concept for tractor beams and demonstrates continuous attraction towards the source, against a net momentum flux in the system.

More on this below.

Viewpoint: A Macroscopic Tractor Beam with Acoustic Waves

Published: 4/30/14

About the Author: Karen Volke-Sepúlveda

(a) Nonconservative pushing force exerted on an object by a plane wave as a result of strong backscattering. (b) Decreasing of the pushing force due to an enhanced forward scattering in a nonparaxial beam. (c) The authors used a target designed to maximize the forward scattering of acoustic radiation, leading to a pulling nonconservative force towards the source: an acoustic tractor beam. Credit: APS/Alan StonebrakerRead more at: http://phys.org/news/2014-05-acoustic-tractor.html#jCp

(a) Nonconservative pushing force exerted on an object by a plane wave as a result of strong backscattering. (b) Decreasing of the pushing force due to an enhanced forward scattering in a nonparaxial beam. (c) The authors used a target designed to maximize the forward scattering of acoustic radiation, leading to a pulling nonconservative force towards the source: an acoustic tractor beam. Credit: APS/Alan StonebrakerRead more at: http://phys.org/news/2014-05-acoustic-tractor.html#jCp

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