固体板背覆薄层特性的低频超声反演方法研究

研究了应用低频超声的反射频谱对固体板厚度及背覆薄层的各特征参数(包括厚度、声速、密度、衰减、声阻抗率、声时)进行反演的方法。从灵敏度函数、目标函数及误差传递方程的角度,对应用反射频谱的谐振频率或幅度谱反演模型系统的单参数和双参数的方法进行了分析讨论。实验使用中心频率为7MHz的探头检测铝板/聚合物薄层样品,在同样的条件下,谐振频率法和幅度谱法反演的单参数反演效果相当,谐振频率方法的双参数反演效果优于幅度谱方法,前者薄层声阻抗率和声时同时反演的平均误差为3.4%和4.7%,而后者没有得到结果。

Research on two inverse methods for characterization of an inaccessible thin film under a plate by low-frequency ultrasound

Two ultrasonic methods for determining the parameters of a composite consisting of a soft thin film attached to a hard plate substrate were studied,by resonance spectra in low frequency region,using its resonant frequencies and amplitude spectra,respectively.An analysis of the sensitivity function,the objective function and the error transfer function were presented for discussing the effect of the two methods for both one parameter and two-parameter inversion. In experimental study,the two techniques were employed to characterize a composite consisting of a film attached beneath to an Al plate substrate with a broadband 7 MHz center frequency transducer.It was observed that the two methods' results were similar for single parameter inversion and the method based on resonant frequencies got better result for two-parameter inversion under the same experimental condition.The relative errors of the method based on resonant frequencies for inversing acoustic impedance and time-of-flight were 3.4% and 4.7%,respectively,and the method based on amplitude spectra got no results.