We use ultrasonic cleaners

We use ultrasonic cleaners routinely for a broad set of applications today. They provide the user with high-efficiency, low-cycle time cleaning with simple push-button operation. Typical ultrasonic cleaners are integrated units. They have a stainless steel cleaning tank, with one or more ultrasonic transducer units fixed to the bottom of the tank. The objects for cleaning are suspended in a stainless steel wire mesh basket placed in the cleaning liquid bath. Once energized, the transducer generates ultrasonic waves throughout the bath that interact with waves reflected from the tank sides to form a ‘stationary’ or standing wave pattern. For a given cleaner and frequency the standing wave pattern is fixed. For enhanced cleaning efficiency, it is advantageous to vary the transducer frequency in some range. This method of operation is the sweep frequency mode, available in high quality ultrasonic cleaner designs. The standing wave pattern formed in the liquid is a collection of alternating compression and rarefaction zones or bands. The distance between bands depends primarily on the frequency and tank geometry. The formation of millions of liquid vapor microbubbles occurs and they rapidly cool and condense back into the liquid, causing high-energy jets of liquid to fill the temporary void created by this condensation. These jets hammer the contaminated objects with a field of high velocity small liquid jets that cause the intense cleaning action. Ideally, for uniform cleaning, their distribution should lie more or less equally across the entire object. The zones of maximal cavitation occur within the rarefaction bands. In case objects suspended in the mesh do not lie entirely within a rarefaction band, the cleaning action there and hence the cleaning efficiency reduces. The sweep frequency circuit continuously alters the transducer frequency in a restricted range. This creates a significant and continuous variation in the location of the compression and rarefaction bands, along with a variation in the distance between them. These band variations subject all parts of the objects to regions of maximal cavitation and cleaning.