Research on nonlinear acoustic attenuation coefficients of material based on second harmonic measurement

The material attenuation coefficients under the action of fundamental and second harmonic wave are measured by the finite amplitude method.Based on the quasilinear theory of KZK equation,the nonlinear sound fields are derived and these beam correction terms are extracted.The measured nonlinear sound pressures using tone-burst are adjusted using these extracted diffraction corrections in order to reduce the impact on the measurement of attenuation coefficients from diffractions.The attenuation coefficients of fundamental and second harmonic are calculated precisely from the linear fitting lines of experiment data.Take water for experiment,the frequency-dependent performance of attenuations is researched and it is found that the attenuation coefficients grows linearly with the frequency in nonlinear experiment,which is different from the case in linear condition that attenuation coefficients show a quadratic correlation with frequency.The research gives a useful method to measure nonlinear acoustic attenuation coefficients and will provide a theoretical basis for the effective application of nonlinear ultrasonic test.