DISTORTION AND HIGH-FREQUENCY GENERATION DUE TO NONLINEAR PROPAGATION OF SHORT ULTRASONIC PULSES FROM A PLANE CIRCULAR PISTON

A numerical finite-difference model for the prediction of nonlinear propagation has been adapted to examine the high-frequency components generated by short ultrasonic pulses. Comparisons are made in both the time and frequency domains between the model predictions and experimental measurements. The experimental measurements were obtained, in water, using a 1-mm-diam membrane hydrophone to sample the pressure field generated by a plane transducer (38 mm in diameter) that was driven by a diagnostic medical ultrasound system. The pulses generated were a few cycles long with a zero-crossing frequency of about 2 MHz and a maximum peak positive pressure of about 300 kPa. It is shown that the theoretical model can be used to provide accurate predictions (typically better than 10%) both on and off the acoustic axis for pulsed pressure fields in water. An important factor in obtaining good agreement is the initial characterization of the transducer and pulse.