Michalakis A. Averkiou Mark F. Hamilton
Dept. of Mech. Eng., Univ. of Texas, Austin, TX 78712-1063
Measurements are reported for finite amplitude acoustic pulses radiated by plane circular pistons in water. Pulses with center frequencies of several megahertz, peak sound pressures up to 1 MPa, durations ranging from approximately 2 to 20 cycles, and different amplitude and frequency modulations were investigated. Measurements of short pulses were made very near the source, where the center wave and edge wave can be separated. Pulse envelope distortion that accompanies shock formation in frequency-modulated tone bursts is demonstrated. Acoustic saturation of pulsed sound beams is also investigated. All measurements are compared with theoretical predictions obtained from a computer code that solves the KZK equation in the time domain [Lee and Hamilton, Ultrasonics International 91 Conference Proceedings (Butterworth--Heinemann, Oxford, 1991), pp. 177--180]. Very good agreement between theory and experiment is obtained both in the near field and the far field, on and off axis. Artifacts in measurements of waveforms containing shocks, which are attributed to bandwidth limitations of membrane hydrophones, are discussed. [Work supported by the Packard Foundation and the Office of Naval Research.]