Levitating and moving small objects with sound waves

Nature : Sound waves have long been known to be able to levitate an object, but only to hold it in place. The technique uses an upward-facing sound emitter paired with a downward-facing reflective surface. Small objects and fluid droplets are suspended at node points—the point in space where the emitted and reflected sound waves cancel each other out. Dimos Poulikakos of the Swiss Federal Institute of Technology (ETH) in Zurich and his colleagues created systems of platforms built from piezoelectric crystals, which change size in response to voltage changes. The setup allowed them to control the location of the node points and thus tow suspended objects from platform to platform. They demonstrated the first successful sonic levitation of multiple objects and the first use of sonic levitation to move objects. On a T-shaped track, they moved two suspended droplets to the joint location where the droplets merged, and then the researchers deposited the combined droplet at the third point of the T.