Using sound waves to levitate individual droplets of solutions containing pharmaceutical drugs and drying them in mid-air. Why do this? This is useful because most of the drugs on the market are either amorphous or crystalline and the crystalline form doesn’t get absorbed by the body. So levitating the solution allows the drug to be made into an amorphous state (by evaporation) because if it were to touch any surface it would simply crystallize. They call this “containerless processing”.
The frequencies used are just above the audible range at about 22 kilohertz and when the two speakers are aligned they create two sets of sound waves, perfectly interfering with each other creating a phenomenon known as a standing wave. This allows the objects to levitate in areas within the waves known as nodes as the acoustic pressure is enough to cancel the force of gravity.