Make liquid droplets dance in air!

What about teaching liquid droplets some salsa in the air?

A team of researchers have successfully demonstrated how to lift and spin liquid droplets - controlling them with high-frequency sound waves.

"The acoustic waves in the ultrasound range at about 160 decibels - too high-pitched for the human ear to hear - made liquid droplets 'dance', hovering in midair, without exploding," said Daniele Foresti, a physicist at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland.

"Our concept is based on three computer-controlled resonators that can create an acoustic standing wave and change its shape in a defined space," said Foresti.

The scientists placed the resonators in a circle. Each computer-controlled resonator created acoustic standing waves at a frequency of about 32.5 kHz.

As the waves' shapes changed, the nodes slowly moved - and the objects hovering above them also moved, said the study published in the journal Physical Review Letters.

To control how high and in what fashion the droplets fly, one simply needs to adjust the sound waves' amplitude (wave height), without modifying the phase, or the position of the wave relative to its origin, the study added.

"By modulating the sound waves, we can 'rotate' the levitation field inside. The system is similar to a three-phase electric motor, but in this case we do not vary the phase of the signal, only the amplitude," added Foresti.

The discovery could lead to potential biological and pharmaceutical applications, such as studying chemical reactions in extreme environments without disturbing them via contact.

The achievement could also reduce wasted material, the study said.