Directivity and Radiation Impedance of a Transducer Embedded in a Lossy Medium
For many reasons in underwater acoustics there is a need for in-situ measurement methods that describe the local acoustical properties of the sea floor. Knowledge of these properties enables one to derive the complex reflection factor under arbitrary angles of incidence, which is an important quantity in modelling sound propagation. Though preference has been given to all methods that operate remotely, no successful breakthrough has yet been achieved in providing a shipborne method that is reliable and easy to handle. In 1977 D. J. Shirley demonstrated that when an acoustical transducer is driven while embedded in the sediment, its radiation impedance depends on the specific acoustical properties of the surrounding environment. Though he gave only laboratory results and did not take into account the attenuation of the sediment, this proposal seems to offer a basis for the development of an appropriate shipborne in-situ measurement method. A prerequisite for such a development is the detailed knowledge of the relationship between the specific complex acoustic data of the sediment and the radiation impedance of the transducer. An analytical treatment of this problem is rather complicated, even under the assumption of compressional waves only. A mixed method of analysis and numerical evaluation is presented.
KeywordsCharacteristic Impedance Directional Pattern Loss Angle Underwater Acoustics Radiation Impedance
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