Underwater low frequency Helmholtz bubble resonator

Abstract

Low-frequency sound sources have found application in oceanology and geoacoustic methods of remote sensing. An underwater low-frequency sound source with a pneumatically driven bubble resonator covered with an elastic membrane effectively provides a very high source level. However, it has a narrow bandwidth, and its resonant frequency is difficult to change without changing the size of the original system. Internal acoustic resonators included in a bubble filled with gas can change the frequency response of the entire source and expand its bandwidth. Internal resonant systems can be designed so that the bubble resonator can be tuned over a wide frequency range. Other systems may add one or more internal resonances and spread the emitted spectrum over a very wide frequency band. It is possible to consider various multipole resonant systems in combination with an underwater bubble. A simple and efficient system consists of a bubble resonator and an internal Helmholtz resonator. The addition of a Helmholtz resonator converts the single resonant bubble into a double resonant system and extends its bandwidth. The theory of the underwater bubble Helmholtz resonator and various applications of these resonators for practical systems are considered. The results of the experimental verification are discussed.