A swept-frequency implosive source

Abstract

Implosive underwater sound sources, such as the 20-liter single-shot device we have constructed, generally emit a rarefaction followed by a compression when the implosion is complete. Some purposes, however, are better served by a swept-frequency, rather than an impulsive, signature, since the lower peak pressures of the swept source are less likely to cause environmental damage. Our current plan for a repeating implosive source operates by venting a bubble (initially at ambient pressure) into a low-pressure receiver through a control valve. Performing this process in steps with abrupt pauses induces oscillations characteristic of the several sizes of the evolving bubble. From modeling the bubble oscillations using the Gilmore bubble equation, it appears feasible to produce a range of a factor of 2 in frequency, with a peak pressure of a megapascal. The design of the control valve, however, is challenging, as it was for the single-shot version. The repeater, however, operates on air, whose density and viscosity are lower.