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A new measurement method for evaluating underwater acoustic materials is proposed. It is based on a two-hydrophones technique and allows the determination of the complex reflection coefficient for size-limited acoustical panels. The results are shown to be independent of the incident plane wave amplitude and the distance between the hydrophones and the panel. Therefore, this technique involves direct and quick measurements so that it is possible to reduce the effects of scattered waves from the edges of the sample by averaging. Simulations have been made to check the stability of the method versus noise. The experiment covered the frequency range 1–12 kHz. Techniques (intensity, impedance, and pressure measurements) tested at G.E.R.D.S.M. (Groupe d'Etudes et de Recherches en Détection Sous-Marine) using surfacic sensors are also presented. Their accuracies are discussed through a mathematical model based on Helmholtz integral equation. Results obtained by the various methods on finite panels are compared.

The air-backed flextensional transducer is particularly sensitive to static pressure stresses. The main limitations are due to shell mechanical resistance and electromechanical bar (or ring) driver amplified stresses. Generally, the design starts with a stress analysis of the shell and driver that yields the relative dimensions of both, according to frequency and power specifications. In spite of optimizated designs, presently most uncompensated flextensional transducers are limited to several hundred meters of immersion. The problem of the static pressure for a class IV and V flextensional transducer is analyzed. A new concept of a specific filtering mechanism for a deeply submerged transducer is presented. Theoretical prediction and experimental results are compared for a 1000-m submerged class IV transducer. Then prospects for future developments are discussed.

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