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A fluid-filled flextensional device for ocean acoustic tomography

Ocean acoustic tomography (OAT) is primarily concerned with the mapping of an ocean interior by the use of acoustic transponders dotted around the periphery of an ocean basin. By measuring the mean time-of-flight of the acoustic emanations between source and receiver pairs and using suitable inversion algorithms, it is possible to obtain a synoptic view of temperature and current flow over areas extending several hundred kilometres. Central to the success of OAT is the development of a low frequency, low Q, high power, compact projector which is able to operate at great depths. In this paper, a pressure compensation method is applied to a barrel-stave flextensional transducer designed for this application. This method entails filling the internal cavity of the device with a low acoustic impedance fluid and inserting a compliant material within the fluid so that the large depth requirements can be met. Finite element methods are used to predict the effect on performance of this configuration for varying volumes of compliant material. The alternative method of free flooding the device is also investigated.