Article Contents

1. Introduction
2. Sweeping Frequency (1)
3. Sweeping Frequency (2)
4. Sweeping Frequency (3)
5. Power Control
6. Center Frequency Control (1)
7. Center Frequency Control (2)
8. Center Frequency Control (3)
9. Center Frequency Control (4)
10. Conclusion

Ideal Ultrasonic Parameters for Delicate Parts Cleaning
(p. 6)

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Center Frequency Control

For the purposes of cleaning, the important parameters are the amount of energy released in a cavitation event, and the density of cavitation events. These parameters have a simple relation based upon bubble size. As the bubble radius increases, the energy released at implosion also increases (table 1). With a constant power input into a liquid, this means that the larger the typical bubble, the fewer total number of bubbles there will be per unit of time. An equivalent way of saying this is to say that, at constant input power, the square of the bubble radius is proportional to implosion energy and inversely proportional to bubble density. Armed with this knowledge we can customize cleaning by modifying the bubble radius, and thus the energy in each event, as well as the number density of events. The most effective way of doing this is by changing the frequency of insonation. Low frequencies allow bubbles plenty of time to grow large, while high frequencies give cavitation bubbles only little time to evolve. This is most clearly illustrated in figure 6 where the resonant bubble radius from equation 1 is plotted as a function of frequency. Controlling the energy in each cavitation implosion is important to prevent pitting or craters on the surface of the substrate being cleaned.

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