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.