Liquid Droplets Floating On Sound Waves In Midair
These drops of solution remain suspended for a long period of time, due to the vibrational force of sound waves that keep them stationary in an air column.
This intriguing video demonstrates the acoustic levitation of liquids on a piece of equipment developed for NASA to simulate microgravity conditions.
The acoustic levitator uses two small speakers to generate sound waves at frequencies slightly above the audible range – roughly 22 kilohertz. When the top and bottom speakers are precisely aligned, they create two sets of sound waves that perfectly interfere with each other, setting up a phenomenon known as a standing wave.
At certain points along a standing wave, known as nodes, there is no net transfer of energy at all.
Because the acoustic pressure from the sound waves is sufficient to cancel the effect of gravity, light objects are able to levitate when placed at the nodes. These drops of solution remain suspended for a long period of time, thanks to the vibrational force of sound waves that keep them stationary in an air column.
Photo by Dan Harris / courtesy Argonne National Laboratory