Results of a systematic investigation of a high intensity sound beam from a plane circular transducer are presented for a large range of excitation levels. The ratio of the shock formation distance to the Rayleigh distance ranges from 1.7 to 0.06. A detailed description of the experimental setup is given. Problems encountered when calibrating highly intense and highly directive sound sources are discussed, and a novel method of calibration is proposed. Experimental results for the case of cw excitation are presented and compared with a simulation using the Bergen Code, thus allowing to assert the usefulness of the model (Khokhlov–Zabolotskaya–Kuznetsov equation) and of the numerical algorithm (spectral decomposition and finite difference method of the transformed beam equation) for high intensity sound beams. A new effect, nonlinear defocusing of the beam, is uncovered.

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Recently, shock wave generators (electrohydraulic, electromagnetic, or piezoelectric) have become of common use for the treatment of renal calculi and gallstones. In all these generators, the focal zone is fixed. This is a major drawback since it is well known that the stones move according to the respiratory cycle. Consequently, the shock waves are not always well focused on the stone, which results in an increase of the duration of the treatment and the development of lesions in the neighboring tissues. To resolve this problem, a piezoelectric electronically focused shock wave generator has been designed. Measurements of the sound field produced in water by the first prototype of this novel generation of extracorporal lithotripters are presented, which clearly demonstrate the advantages of this type of focusing.

La caractérisation des céramiques piézoélectriques s'effectue habituellement à partir de modèles unidimensionnels décrits dans les normes EEE. Les modes sont supposés découplés ce qui n'est pas le cas pratiquement Le mmodele tridimensionnel de vibration d'un disque épais piézoélectrique prend en compte à la fois les cou~larres élastiaues et ~iézoélectriaues ainsi aue les vertes mécaniaues du matériau. Le but de ce travail est I'utiÎisa2on des t&hniqu& dbptimisaGon pour idêntifier Simultanément les résonances radiales et axiales d'un disque céramiaue. La méthode numériaue mise en oeuvre est la méthode du SIMPLEXE qui est bien adaptée au cas où il y a un gxand nombre de à déterminer. Nous nous sommes particulièremënt intéressés àmontrer l'influence des paramètres de couplage C12, Cl3 et h31 sur la forme des courbes de résonance obtenues.