Saturation Work

The maximum value of acoustic pressure within an ultrasonic beam is limited by acoustic saturation. The theoretical basis for acoustic saturation has been analyzed previously. In this work, a high-power pulse source is used to drive acoustic pressure levels from an ultrasonic beam to saturation. An automatic procedure determines the field's beam axis using a calibrated Marconi PVDF hydrophone. The hydrophone measured RF waveforms are recorded along the beam axis and analyzed off-line. The peak compressional pressure is evaluated as a function of distance along the beam axis. The overall maximum pressure is compared to theoretical predictions. Three-, six-, and nine-MHz center frequency, 19-mm-diameter transducers were analyzed. The longer focal length transducer saturation level was comparable to a theoretical prediction. However, the theoretical saturation level for the shorter focal length transducers underestimated experimental results. Below is a plot of peak compressional pressure vs. applied voltage for a 9-MHz f/2 and 9-MHz f/3 transducer. Also indicated is the theoretical prediction P_sat.