Nonlinear parameter measurement and transient acoustic field imaging using the parametric interaction in liquids

The parametric interaction of two ultrasonic waves having a high frequency ratio is exploited for measuring the nonlinear parameter of liquids and for plotting the velocity field of transducers. Assuming a weak nonlinearity, we show that the interaction of a high frequency continuous wave with a low frequency pulse is equivalent to a phase modulation of the high frequency wave. Consequently the information on the non-linearity of the medium and the low frequency velocity field are extracted by demodulating the continuous wave phase. The advantage of this original method is that measurements are not disturbed by the nonlinear diffraction effects. We also use a comparison method to measure the nonlinear parameter without any transducer calibration