Acoustic tractor beam.
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.
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom.
Christine E M
CE
Démoré
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom and Department of Physics, Illinois Wesleyan University, 201 East Beecher Street, Bloomington, Illinois 61701, USA.
Patrick M
PM
Dahl
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom.
Zhengyi
Z
Yang
Engineering Sciences, University of Southampton, University Road, Southampton SO17 1BJ, United Kingdom.
Peter
P
Glynne-Jones
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom.
Andreas
A
Melzer
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom.
Sandy
S
Cochran
Institute for Medical Science and Technology, University of Dundee, 1 Wurzburg Loan, Dundee DD2 1FD, Scotland, United Kingdom and Division of Physics, University of Dundee, Nethergate, Dundee DD1 4HN, Scotland, United Kingdom.
Michael P
MP
MacDonald
Department of Physics, Illinois Wesleyan University, 201 East Beecher Street, Bloomington, Illinois 61701, USA.
Gabriel C
GC
Spalding