High level, low-frequency, plasma-induced bubble transducer

Conventional low-frequency transducers are rather bulky, of limited efficiency, and may suffer from cavitation at high source levels. Plasma-induced bubble transducers may offer improvement in some of these limiting factors. An implementation method for these devices that has demonstrated precise energy control into the plasma has been developed. This has resulted in the ability to produce high level, high spectral efficiency sound at low frequency in a very compact geometry. Results are presented for sustained oscillations of a large plasma-induced bubble which has produced transient sound levels as high as 215 dB. This offers the opportunity to produce very high sound levels on a cw basis. Our experiments have demonstrated the ability to stabilize bubble motion due to buoyancy, reexcite bubble oscillations with high efficiency, and the use of closed-loop feedback control for timing of energy injection. Experimental results of the acoustic output and bubble motion are presented. [Work supported by the U. S. Navy.]