|Credit: Physics World (link below)|
An acoustic "tractor beam" that can pull an object by firing sound waves at it has been created by physicists in the UK and US. The beam was made using a commercial ultrasound surgery system and differs from previous tractor beams that use light. The researchers say their technique could be readily adapted for medical applications that manipulate objects or tissue within the body.
The new tractor beam has been created by Mike MacDonald and colleagues at the University of Dundee, University of Southampton and Illinois Wesleyan University by using an ultrasound ablation system, which is normally used to destroy tumours thanks to focused beams of intense sound. First proposed in 2006 by Philip Marston of Washington State University and realized using light in 2010 by David Grier and colleagues at New York University, the technique involves firing two beams of ultrasonic waves upwards at a triangular-shaped target at about 51° either side from the vertical direction. The target is shaped such that the beams bounce off opposite sides of the triangle, causing the reflected sound to travel straight up (see figure "Reflecting beams").
Physics World: Physicists sound-out acoustic tractor beam