1197. How does an ultrasonic bath work? — PT
An ultrasonic cleaner exposes a bath of liquid to very intense, very high frequency sound. Sound itself consists of regions of high and low pressure that move through a material as waves. As these waves pass through the liquid in the bath, each tiny portion of liquid vibrates back and forth in response to these pressure fluctuations. Near the surface of an object immersed in the bath, the liquid is pushed first toward the object and then away from it. The pressures involved are large and the changes in velocity within the liquid are so intense that occasionally the liquid will actually pull away completely from the object so that a tiny empty cavity forms. In effect, the liquid is jumping up and down on the object's surface and it occasionally jumps so hard that it leaves the surface altogether. Cavities of this sort are unstable and the liquid soon returns to the object. When it does return, the liquid collides violently with the surface and the liquid's pressure skyrockets as it transfers all of its momentum to the object in millionths of a second. This "cavitation" process is what cleans objects immersed in the ultrasonic bath—the dirt and grime are pounded free by the liquid when it returns to fill cavities that have formed during the vibrations.