People have been able to levitate small objects using sound for years. But applications for the technique are severely limited because scientists hadn't figured out how to control and manipulate the floating objects. Until now.
The idea of acoustic levitation is certainly not new. Several levitation methods exist today, including using electrostatic forces, magnetism and light. But each of these techniques has it own drawback. For example, light can only manipulate matter that's very tiny (up to about 50 microns, the size of a human liver cell), whereas magnetic levitation requires the material to have special properties.
Sound waves, on the other hand, can float larger objects, independent of material properties. The basic setup requires an acoustic emitter and a reflector placed some distance away. When the sound is turned on, it bounces off the reflector and back towards the emitter.
The two opposing waves (emitted and reflected) interfere with one another, creating a standing wave. Certain parts of the wave, called nodes, don't move. And when the standing wave is parallel with gravity, some portions of it have a constant downward pressure and other portions have a constant upward pressure -- the nodes, however, have very little (virtually zero) pressure.