キャビテーションを伴うパルス超音波の音圧波形

抄録

Pressure waveforms of pulsed ultrasonic waves by which cavitation is produced in aerated water are observed by a miniature barium titanate microphone. A laminated nickel transducer with a simple vibration pickup attached on its back surface is used at its resonant frequency of 24 KC to radiate the pulsed ultrasonic waves. At the pulse width of 0. 3ms, only a few cavitations are produced, so that individual shock waves caused by the collapse of cavities are observed as sharp impulses of about 0. 5 μs width during the decreasing phase of pressure waves. At the intensified pulse of 1. 5 ms width, the pressure waveform is no longer sinusoidal owing to the production of many cavitaitons, but is turned into saw-toothed form with large positive peaks instead. When the ultrasonic pulse is built-up, the first cavitation occurs at the decreasing phase subsequent to the second pressure maximum. The production of cavitation continues over several successive periods at nearly the same pressure phase as the first one, and the intensity of cavitation becoming less violent at every other period. Thus the subharmonic component appears on the pressure waveform, and, simultaneously, on the vibration of the transducer, too. As the generation of remarkably distorted wave is localized near the center of the radiating surface where the violent cavitation occurs, the saw-toothed waveform fades out rapidly as the distance increases from the transducer, and the waveform at a distance becomes similar to the velocity waveform of the transducer.