A bank of speakers can grip, move and rotate particles in air from one side (pictured).
Sound has been used to levitate small objects, but single-sided devices offered little manoeuvrability. Asier Marzo at the Public University of Navarre in Pamplona, Spain, and his colleagues used a flat array of 64 loudspeakers to levitate beads of polystyrene up to 3 millimetres wide. The authors used algorithms to create interference patterns in waves of ultrasound that formed regions of high and low intensity — shaped as tweezers, tornadoes or bottles — which allowed them to trap and then move the particles in various directions.
The device could be used to manipulate particles for targeted drug delivery or to operate tiny surgical devices from outside the body, say the authors.
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Beads dance on sound waves. Nature 527, 10 (2015). https://doi.org/10.1038/527010a