Description
Acoustic levitation uses the radiation pressure of standing sound waves to suspend small objects at the nodes of a standing wave pattern — the points where the acoustic pressure is at minimum and the acoustic radiation pressure creates a stable equilibrium trapping objects. This laboratory setup uses two facing ultrasonic transducers operating at 22kHz (above human hearing) with a precisely controlled separation that creates standing waves with nodes every 7.7mm. A water droplet of approximately 3mm diameter is shown at one of these nodes, its shape flattened from a sphere to an oblate spheroid by the acoustic pressure field. Shot at 1/4000 second under studio lighting against a dark background, the droplet’s spherical reflections and the water surface tension behaviour are clearly visible. The levitating droplet appears to violate gravity — a physical phenomenon made visible through photography.
