Michel Letiche
Thomson Sintra ASM-525, Route des Dolines, BP157, 06903 Sophia Antipolis Cedex, France
Flextensional transducers consist of a piezoelectric or magnetostrictive driver and a mechanical shell. The shell, excited on its first bending mode, amplifies the acoustic radiation. In a first part, the coupling between the driver and the shell is analyzed. The relative resonance frequency of each element determines the resonance frequency of the transducer and its radiated acoustic power. Furthermore, in most cases, operating depth is a significant limitation in the design of this kind of source---classical flextensional transducers on the work market are typically depth limited at about 200 or 300 m. To avoid the effects of the hydrostatic pressure, mechanical filters have been developed. The aim of these devices is to make the driver and the shell independent under static conditions. An equivalent scheme model is used to understand and to design this filtering element. Theoretical results are presented and a great depth class V flextensional transducer has been developed using this original technology. Its acoustic and static behaviors have been optimized with an axisymmetric B.E.M./F.E.M. numerical code. Finally, theoretical results are discussed in comparison with experimental ones obtained with the CERDSM facilities in Castillon Lake. Finally acoustic performances of this low-frequency, high power, and great depth transducer are shown. [Work supported by DRET.]