ASA 124th Meeting New Orleans 1992 October

1aEA5. A systematic experimental investigation of a highly intense pressure field generated by a plane circular transducer.

Sylvain Nachef

Technomed International S. A., Bron, France

INSERM unite 281, Lyon, France

Dominique Cathignol

INSERM unite 281, Lyon, France

Jacqueline Naze Tjotta

Univ. of Bergen, 5007 Bergen, Norway

This work is part of a study of highly intense sound beams with application to medical therapy in mind. A systematic experimental investigation of a sound beam propagated into water from a plane circular transducer was for the first time, it is believed, performed for a large range of cw excitation levels. The fundamental frequency was 1 MHz and the on-source pressure ranged from 0.8 to 24 bar (shock formation distance to Rayleigh distance ratio ranging from 1.8 to 0.06). The pressure amplitude distributions of the five first harmonic components, along and across the acoustic axis, are presented and discussed. New nonlinear effects are uncovered: a nonlinear self-defocusing of the beam and an alteration of the near-field structure of the harmonic components.