The locations of peak pressures and peak intensities in finite amplitude beams from a pulsed focused transducer.

Abstract

The effect of finite-amplitude distortion on the positions of peak pressures and peak intensities in beams generated in water by pulsed focused transducers has been investigated experimentally. The pulses generated by three single-element, circular, focused transducers with nominal frequencies of 2.25, 3.5, and 5.0 MHz have been investigated with pressures at the transducer P0 being varied over the range 10 kPa to 1.4 MPa. Measurements were made using a 9 micron thick polyvinylidene difluoride membrane hydrophone. In all cases the locations of peak pressures were not stationary as the field strength was altered. As P0 increased, the distance from the transducer to the positive peak initially increased, and then decreased. The distance to the negative, or decompression peak decreased monotonically with increasing P0. The location of peak pulse intensity integral was found to alter slightly with power, taking a position between the peak positive and negative pressures.