Ultrasonic cleaning is achieved through a process called cavitation. There are two types of cavitation: inertial (or transient) and non-inertial. Non-inertial cavitation is what is employed in ultrasonic cleaning tanks and is a phenomenon whereby rapid changes of pressure in a liquid lead to the formation of small vacuum chambers or cavities in places where the pressure is relatively low.
In a cleaning tank, these low-pressure areas are generated through the flexure of a radiating face, which can either be the base or the sides of the tank. This flexure is caused by the action of transducers that are firmly attached to the tank that, when excited by high frequency electricity expand and contract at an incredibly fast rate.
On the downward flex, the low pressure area is created and on the upward flex, the low pressure area is released into the tank fluid the form of a vacuum bubble or chamber, which will grow as it rises up through the tank fluid until it hits an object, where upon it will collapse, thus creating a higher pressure area. Through this high-speed collapse, a micro-jet is formed and contamination on the surface of any item being cleaned is sucked away.
However, not all ultrasonic cleaning systems are created equally and it should be noted that in commercial grade systems, when the vacuum bubbles are created, they are done so in an erratic and un-even manner, thus making the distribution of the cleaning action potentially inconsistent. When cleaning general parts, or say jewellery or glasses etc., this un-even cleaning action is inconsequential.
However, if precision cleaning is required as in the case of surgical instruments and anilox rolls for example, a more advanced application of the sound is needed to deliver the safe and precise formation and distribution of vacuum bubbles that these applications require.