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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What is "Ultrasonics?"

Ultrasonics is the science of sound waves above the limits of human audibility. The frequency of a sound wave determines its tone or pitch. Low frequencies produce low or bass tones. High frequencies produce high or treble tones. Ultrasound is a sound with a pitch so high that it can not be heard by the human ear. Frequencies above 18 Kilohertz are usually considered to be ultrasonic. The frequencies used for ultrasonic cleaning range from 20,000 cycles per second or kilohertz (KHz) to over 100,000 KHz. The most commonly used frequencies for industrial cleaning are those between 20 KHz and 50KHz. Frequencies above 50KHz are more commonly used in small tabletop ultrasonic cleaners such as those found in jewelry stores and dental offices.

The Theory of Sound Waves

In order to understand the mechanics of ultrasonics, it is necessary to first have a basic understanding of sound waves, how they are generated and how they travel through a conducting medium. The dictionary defines sound as the transmission of vibration through an elastic medium which may be a solid, liquid, or a gas. Sound Wave Generation - A sound wave is produced when a solitary or repeating displacement is generated in a sound conducting medium, such as by a "shock" event or "vibratory" movement. The displacement of air by the cone of a radio speaker is a good example of "vibratory" sound waves generated by mechanical movement. As the speaker cone moves back and forth, the air in front of the cone is alternately compressed and rarefied to produce sound waves, which travel through the air until they are finally dissipated. We are probably most familiar with sound waves generated by alternating mechanical motion. There are also sound waves which are created by a single "shock" event. An example is thunder which is generated as air instantaneously changes volume as a result of an electrical discharge (lightning). Another example of a shock event might be the sound created as a wooden board falls with its face against a cement floor. Shock events are sources of a single compression wave which radiates from the source.

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