DGA--DCN--DCN Toulon CERDSM, Le Brusc, 83140 Six-Fours-Les-Plages, France
In this paper, a one-sided flextensional projector, which has been designed and constructed, is presented. Roughly, it looks like a class IV flextensional transducer but with only a partial aluminum shell defining the radiating part. Inside the shell, longitudinal piezoelectric stacks are tightly inserted, with regular spacing, parallel to the shell pseudo-major axis. Steel inserts are fixed at both ends of these stacks and conventional tie rods are used for prestressing. A steel housing situated behind the shell as well as top and bottom caps ensure watertightness. Under an electrical drive, the stacks undergo a longitudinal vibration that is transmitted to the shell and converted into flexural motion with a larger mechanical displacement. Nevertheless, despite the similarities, the operating mode of this projector is very different from the conventional flextensional operating principle. Such an original behavior has been obtained by a careful design of the transducer. A trial-and-error procedure has been carried out with a numerical analysis tool to optimize the main electromechanical parts. Fairly accurate comparisons with experimental results have been obtained for the transmitting voltage response as well as for directivity patterns. It is confirmed that this one-sided flextensional transducer is directive, leading to a front-to-back ratio equal to about 10 dB in the frequency range of interest. Close-packed arrays can be easily realized with the one-sided flextensional transducer type. Some new array designs are discussed and illustrated with theoretical results.