Determination of nonlinear parameter in liquid based on diffraction correction using multi-Gaussian beam model

It is significant to determine nonlinear parameter β using nonlinear ultrasonic test for the evaluation of material characteristics, such as mechanical properties and early fatigue damages. A measurement method of β independent of the measuring distance is proposed in order to improve the performance that the present finite amplitude method only works in the near-field region of finite-size transducers. Attenuation and diffraction corrections for measured fundamental and second harmonic wave displacements are taken into account to reduce the impact on sound energy losing and field spreading, in which a more accurate diffraction correction for second harmonic wave using multi-Gaussian beam is conducted. Determining nonlinear parameter β with considerations of diffraction and attenuation can reduce the difference between the measured value and theoretical one and improve the accuracy in different measuring distances. Determination of β in water is simulated in theory and verified with experiment, and the results both show the developed method has the advantage of high precision over other methods. It is also proved that the proposed method is independent of the measuring distance and provides the theoretical basis for application of nonlinear ultrasonic test in less strict conditions.