衍射和衰减修正下材料非线性系数的检测方法

摘要

为提高有限幅值法测量材料非线性系数β的精度，给出了一种基于衍射和衰减修正的测量方法：由 KZK方程入手，以平面波解、衰减修正和衍射修正组合的形式描述有限孔径的探头产生的声场，其中采用25组高斯声束实现衍射修正的准确快速计算；运用非线性最小二乘拟合原理提取基波和二次谐波的衰减系数，并根据实测的衰减系数实现声场的衰减补偿。通过检测声压值的衍射和衰减修正有效抑制声束扩散和声能衰减对β测量结果的不利影响，提高其检测精度。以水的β测量为例进行了实验验证，结果表明采用该方法检测的β值误差＜5％，且不受测量距离的限制，为精确测量材料非线性系数提供一种有效方法。%A more precise approach to determine the nonlinear acoustic parameter of materials using finite amplitude method was proposed based on the diffraction and attenuation corrections.Developed from the KZK equation, the fundamental and second harmonic sound fields generated by finite size transducers were described as the combination of plane wave solutions,attenuation and diffraction corrections,in which,the diffraction corrections could be calculated by using 25 groups of Gaussian beam models quickly and accurately.Attenuation coefficients of the fundamental and second harmonic components were extracted based on a nonlinear least squares curves-fitting method,which can be used to obtain more effective attenuation corrections.With the diffraction and attenuation corrections,the measured fundamental and second harmonic sound pressures were adjusted to reduce the impact on measuring from field spreading and sound energy losing,and the measured results are more accurate.The of water was investigated in experiment,the results show that the errors of the measured values are within 5% by using the proposed approach.In addition,it is also proven that the proposed approach is independent of the measuring distance which is an effective tool to improve the precision of measuring the nonlinear parameter.