Finite amplitude ultrasound beams

Finite amplitude effects occurring in ultrasound beams with a moderate to high level of excitation are reviewed. Experimental evidence is shown, based on results from investigations that involve ultrasound transducers at various levels of excitation. Comparison with theoretical predictions from existing models for nonlinear propagation of a diffracting sound beam in a dissipative fluid, shows that the Bergen Code, which represents a numerical implementation of the Khokhlov-Zabolotskaya-Kuznetsov and related equations, provides an excellent simulation for ultrasound beams produced by transducers of various shapes when the level of excitation is low to moderate. Discrepancies observed between experiment and theory when the level of excitation is high are discussed. Preliminary estimates are given of nonlinear effects that are not accounted for in the above mentioned models, as the mean motion (acoustic streaming), rise in ambient temperature, and related forces induced by sound waves in a dissipative fluid. New model equations that account for cubic order terms and include the above mentioned finite amplitude effects of ultrasound are presented. Problems encountered when calibrating highly intense ultrasound transducers are also addressed