Using a series of standing ultrasound waves, it is possible to suspend small particles at the sound pressure ... to localize the pressure node, or focal point, and levitate small objects around ...

The sound is, as the name implies ... fixed in mid-air where there’s a pressure minimum in the standing wave. [Olimex] has created a small ultrasonic levitation kit that exemplifies this ...

For the bubbles, the duo utilized an acoustic levitation machine – a specialized instrument designed to suspend objects mid-air using sound waves by creating acoustic radiation pressure.