Acoustic cavitation. In a non-flowing system the ambient pressure can be varied by sending sound waves through the liquid. The ultrasonic sound waves are made up of alternate compressions and rarefactions. During the rarefaction cycle (low pressure) a lot of microscopic bubbles will grow and during the compression cycle (high pressure) each bubbles undergoes a collapse or implosion. These implosions of the bubbles produce shock waves in the liquid. These shock waves produced during the ultrasonic cleaning will reach any solid surface that is in the ultrasonic tank liquid. The ultrasonic cleaning method is important because by using the ultrasound,it is possible to take the scrubbing action into the "nooks and crannies" that would be inaccessible with a mechanical scrubbing brush.