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Name: David S.
Status: Student
Age: 18
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Date: N/A


Question:
Can cavitation or a similar effect be created in a substance (water)with the use of sound waves that come from a source other than the mechanical disturbance from surfaces such as the prop or other parts that are highly frictional? (in other words can sound waves transmitted through a surface ((of a submarine for instance)) with little friction produce cavitation?)



Replies:
Yes, an object vibrating with enough amplitude at the correct (typically ultrasonic) frequency will also cause cavitation in a liquid. The amplitude of vibration does not have to be very large - less than an millimeter will do.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois


Yes. Anything that can make a big enough local reduction in pressure can cause cavitation.

Tim Mooney


Ultrasonic transducers are commonly used in laboratories to produce cavitations for many applications, especially for making dispersions and for breaking open cells of various types.

The U.S. Navy is conducting research for using cavitations to "encapsulate" entire submarines in a cavitations bubble that would allow much faster speeds than presently available, maybe 100 mph. See:

http://www50.dt.navy.mil/facilities/LCC.html

In the last year, maybe two, Scientific American described the use of ultrasonic reverse echo technology to produce highly amplified and concentrated beams of acoustic energy for precision non-invasive surgery. Roughly the principle is: from a focus point generate a weak signal of acoustic energy. This is picked up by an array of transducers surrounding the patient. Store the signals digitally, amplify them, then send them back to the focus reversed "first-in-last-out" fashion, rather than the "first-in-first-out" way conventional echoes occur. This refocuses the acoustic energy precisely at its original source, but with much higher amplitude that kills the cells at the source, but not in nearby tissue because the convergence in not sufficient to cause cell damage except at the precise point where the acoustic wave originated.

Vince Calder



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