Scientists at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland have designed an acoustic levitator capable of controlling and mixing substances as they hover between two platforms.

The device is built of two facing platforms made up of sound-emitting squares that trap the substances between them. The sound waves move upward until they reach the surface lying above, whereupon they bounce back. When upward and downward-moving waves overlap, they cancel out and trap materials in place.

This requires extremely powerful sound to levitate even a tiny droplet of water, so the researchers have worked with ultrasound - frequencies beyond those that human ears can detect - to avoid damaging their hearing.

Researcher Daniele Foresti explained that, although acoustic levitators were not a new concept, this was the first one able to move and control the material it levitated.

"We have total control of the acoustic field inside," he told BBC News.

This clip show the result of that control, with a droplet of water and a particle of sodium metal "dancing" between the two platforms and coming together to react.

Footage courtesy of Daniele Foresti and Dimos Poulikakos