An array of ultrasound beams can drag centimetre-sized objects towards it.

Mike McDonald at the University of Dundee, UK, Gabriel Spalding at Illinois Wesleyan University in Bloomington and their colleagues sculpted interference patterns in the array so that much of the acoustic energy bounced off the sides or rear of an object in front of the array. This drove the object towards the ultrasound sources. The effect has been previously shown with light waves, but sound waves can move larger objects.

Such control might prove useful in non-invasive surgery: for example, it could be used to manipulate drug-delivery packages inside the body or to precisely cut out tumours.

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