Acoustic Nonlinearity in the Derating Problem for HIFU Sources

Abstract

Numerical simulations of focused acoustic beams are performed in water over a wide range of linear gains and source amplitudes, in order to demonstrate the combined effect of acoustic nonlinearity, diffraction, and focusing on extrapolation (derating) of the main parameters of high intensity acoustic fields at the focus from the linear theory. It is shown that nonlinear corrections to the focusing gain are different for different parameters of the acoustic field and for different values of the linear gain. Nonlinear enhancement of the focusing gain is found to be more pronounced for the peak positive pressure and for higher linear gains. The levels of nonlinear saturation for various parameters of the field at the focus are obtained for very high source amplitudes. The results of simulations give higher saturation levels compared to the approximate analytic predictions.