The effect of receiver size on nonlinear pressure field measurements

The nonlinear pressure field generated by an ultrasonic source many wavelengths in diameter is studied experimentally and theoretically using two different size receivers. One receiver is sufficiently small to be considered infinitesimal at most positions in the pressure field while the other receiver has a diameter equal to that of the source. Theoretical predictions are made using a numerical solution of the KZK equation and these show that the large receiver virtually eliminates the pressure field fluctuations normally observed with a small receiver along and across the acoustic axis. To a large extent the axial field observed with the large receiver resembles a plane-wave field. The predictions are compared with experimental measurements obtained with a plane piston transducer (38-mm-diam, 2,25-MHz center frequency) as a source, and hydrophones 1 mm and 38 mm in diameter. Good agreement is seen between experiment and theory. (C) 1996 Acoustical Society of America.