Acoustic levitation of water droplets

These water droplets are not falling; they’re actually stuck in place. What we’re seeing is the effects of an acoustic levitator. The device was initially developed by NASA to simulate microgravity. Now it’s being used by the pharmaceutical industry do develop better drugs.
The two parts of the apparatus seen in the image above are both speakers. They put out a sound at about 22 kHz, which is beyond the human range of hearing. When precisely aligned they interfere with each other and create a standing wave. The droplets are trapped in the nodes of that wave.

Sursa: http://hackaday.com/2012/12/06/acoustic-levitation-of-water-droplets/