'Acoustic tweezer' tractor beam could replace invasive surgeries

Beating the tractor beam's limits

Researchers have been trying to manipulate objects using sound or light for decades, with some success - with very tiny objects at least. Now a new technique has been developed that to levitate and move larger objects, using swirling tornadoes of sound.

The limitation the researchers have overcome with their new "acoustic tractor beam" was determined by the wavelength of the sound being used. In a 'field' of sound there are areas where waves interact and are either in phase or out of phase. These create nodes of high intensity (in phase) and low intensity (out of phase).  These nodes are where anything that you are trying to levitate likes to collect.  Anything larger than one wavelength can't sit in either node and is unstable in the sound field.  So previous technologies were limited by the tiny wavelength of sound.

• Research paper in Physical Review Letters

Twin tornadoes cradle levitated objects

Now, Asier Marzo and colleagues at the University of Bristol have beaten that limit by creating tornadoes of sound by alternating the direction of the sound emitted. Two tornadoes swirl around on top of each other like ice cream cones connected at their points and the object to be levitated - a styrofoam ball in their experiment - floats in space at that junction. By simply changing the parameters just a bit the styrofoam ball can be pulled towards the device just like a tractor beam.

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The researchers hope that one day an acoustic tractor beam can be developed to move things around in the human body. A sound-powered tractor beam could be developed to penetrate the deep tissues of the body like ultrasound but instead of just visualizing the inner organs, it would be able to move things like kidney stones, deliver drugs to specific places or manipulate small parts of the body.