The nonlinear pressure field of a plane circular piston: Theory and experiment

The measured nearfield pressure levels of a plane circular piston are compared with a numerical solution of the parabolic approximation to the nonlinear wave equation under conditions of high nonlinearity (100 kPa at the piston face). The solution allows for nonlinearity, diffraction, and absorption in continuous wave pressure fields. The measurements were made in water, using a transducer (38-mm diameter) driven at 2.25 MHz and a 1-mm-diam membrane hydrophone. Comparisons are made along and across the acoustic axis for the amplitudes of the fundamental, second, and third harmonics and the phases of the second and third harmonics. Good agreement is shown between experiment and theory within the known limitations of both.