The effect of nonlinear distortion of biomedical ultrasound on acoustic cavitation Free

Previous theoretical studies of acoustic cavitation postulated as the driving pressure a Gaussian pulse, a sine wave within a Gaussian envelope, or a pure‐tone sine wave. In this study, the harmonic components of a distorted sine wave are calculated following the method of Blackstock [J. Acoust. Soc. Am. 39, 1019–1026 (1966)]. The magnitudes of these harmonics are attenuated as a function of frequency and distance from the transducer and are summed using a constant phase shift. This produces a waveform quite similar to those seen in the laboratory. Distorted waves produced at 1, 3, 5, and 10 MHz are used to derive Cramer's equations for nonlinear bubble dynamics [Cavitation and Inhomogeneities in Underwater Acoustics, edited by W. Lauterborn (Springer, New York, 1980), pp. 54–63]. Typical bubble radius versus time curves and transient cavitation thresholds (R/R_n, > 2.0) are shown. Due to the shifting of energy from the fundamental to the harmonics and to attenuation, these thresholds are generally higher than for pure sine waves. [Work supported by NIH.]