Article Contents

1. Introduction
2. What is "Ultrasonics?"
3. Nature of Sound Waves
4. Cavitation and Implosion
5. Benefits of Ultrasonics
6. Ultrasonics Speeds Cleaning
7. Complex Contaminants
8. Ultrasonic Generators
9. Pulse and Frequency Sweep
10. Frequency and Amplitude
11. Magnetostrictive Transducers
12. Piezoelectric Transducers
13. Ultrasonic Cleaning Equipment
14. Maximizing the Cleaning Process
15. Maximizing Cavitation
16. Minimizing Dissolved Gas
17. Maximizing Overall Cleaning Effect (1)
18. Maximizing Overall Cleaning Effect (2)
19. Conclusion

Ultrasonic Cleaning: Fundamental Theory and Application
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Cavitation and Implosion

In elastic media such as air and most solids, there is a continuous transition as a sound wave is transmitted. In non-elastic media such as water and most liquids, there is continuous transition as long as the amplitude or "loudness" of the sound is relatively low. As amplitude is increased, however, the magnitude of the negative pressure in the areas of rarefaction eventually becomes sufficient to cause the liquid to fracture because of the negative pressure, causing a phenomenon known as cavitation. Cavitation "bubbles" are created at sites of rarefaction as the liquid fractures or tears because of the negative pressure of the sound wave in the liquid. As the wave fronts pass, the cavitation "bubbles" oscillate under the influence of positive pressure, eventually growing to an unstable size. Finally, the violent collapse of the cavitation "bubbles" results in implosions, which cause shock waves to be radiated from the sites of the collapse. The collapse and implosion of myriad cavitation "bubbles" throughout an ultrasonically activated liquid result in the effect commonly associated with ultrasonics. It has been calculated that temperatures in excess of 10,000°F and pressures in excess of 10,000 PSI are generated at the implosion sites of cavitation bubbles.

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