WATCH: Sound waves suspend a mesmerizing midair chemical reaction
An "acoustic levitator" makes small particles hover and dance
Scientists have been able to levitate objects with sound waves for some time, though the process has typically suffered from a lack of precision and control.
Now, researchers at the Swiss Federal Institute of Technology (ETH) have developed an "acoustic levitator" that allows them to suspend and then carefully move small substances, like water droplets, between two reflective panels.
Transmitters arranged in a row beneath one of the panels do the heavy lifting. When sound waves emitted by those transmitters echo back off the opposite panel, the two competing, overlapping forces cancel each other out, trapping particles in space.
By upping the power on an adjacent transmitter, particles can be coaxed into moving laterally. That's what you see in the video above, in which a sodium particle is thrust into a water droplet, triggering a suspended chemical reaction.
The trick requires an extreme amount of acoustical force, so the team had to use a frequency beyond what the human ear can detect — think a really powerful dog whistle.