Underwater impulsive acoustical generation from steam bubbles

Abstract

One of the most common techniques to generate impulsive sound underwater is through the use of sparkers. The sound is generated through high-voltage arcing across two electrodes. Research at NCCOSC, RDT&E division has shown that modest sound levels can be produced from electrodes operated at nonarcing voltages. In this mode the main products in the electrode spacing are steam bubbles. The expansion and subsequent collapse of a single steam bubble is what generates the underwater sound. The advantages to the use of nonarcing electrodes are longer electrode life, greater reproduciblity, and the use of light-weight components. The disadvantages include lower electroacoustical conversion efficiency and lower electrical power input. The electroacoustical conversion efficiencies measured reached 0.7%. Extrapolation of efficiency data show that 1% or better efficiency may be achievable. A high-speed imaging was developed to capture the history of events in the electrode spacing. Images of various bubble events are shown and interpreted. [Work supported by ONR.]