Bubble Influence on the Behaviour of Sea-Water Plasma-Based Sound Sources

Bubble phenomena in underwater sound sources are studied from a theoretical and experimental point of view. To start an analytical approach to the problem, the formation of vapour bubbles in the liquid during an electrical discharge was studied by implementing and solving a complete set of equations for the description of Joule heating both in time and space. The nonlinear equations governing the temperature and the electric potential in the liquid were solved numerically and validated by a direct comparison with experimental data. These data were obtained by measuring the acoustic pressure pulses as a function of time, for different electrode distances, and measuring voltage and current across the spark gap during the discharge. The bubble contribution to the radiated acoustic energy seems to be governed by geometric and electric parameters, giving a fairly controllable and predictable result in the electrical and acoustic behaviour of sparker sources. Therefore, a careful choice of these parameters is needed to optimize the system performance, namely acoustic efficiency, signal bandwidth and resolution.