材料非线性衰减系数的二次谐波测量方法研究

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

采用有限幅值法测量材料在基波和非线性引起的二次谐波作用下的衰减系数:利用准线性下的KZK方程推导基波和二次谐波的声压分布,并提取波束修正系数;采用短纯音信号进行非线性实验,对检测得到的基波和二次谐波声压进行衍射修正处理,有效抑制衍射对衰减系数测量的不利影响,继而通过线性拟合的方法计算得到更精确的基波和二次谐波的衰减系数。以水为例进行实验,研究了实验测量所得衰减系数的频率依赖关系,结果表明在非线性条件下水的衰减系数与频率间存在较强的线性关系,而线性条件下衰减系数随频率呈现二次方增长的特性则不适用于非线性条件。该研究提出了准确测量非线性声波衰减系数的方法,为更有效地应用非线性超声检测提供理论依据。

The material attenuation coefficients under the action of fundamental and second harmonic wave are mea- sured 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 correla- tion 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.