基于声压反射系数幅度谱匹配分析的薄层厚度和超声纵波声速双参数反演

Simultaneous Inversion of Thickness and Ultrasonic Longitudinal Velocity for Thin Layered Structure Based on Ultrasonic Reflection Coefficient Amplitude Spectrum Matching Analysis

针对薄层材料超声测厚过程中回波信号混叠、超声纵波声速未知导致薄层厚度无法测量的问题,提出一种基于声压反射系数幅度谱（Ultrasonic Reflection Coefficient Amplitude Spectrum,URCAS）匹配分析技术同时测量薄层厚度和超声纵波声速的方法。采用相关系数法对薄层试样实测声压反射系数幅度谱和理论声压反射系数幅度谱在超声检测有效频带范围内逐一进行匹配分析,通过反演计算得到相关系数最大值点对应的超声检测参数,最终实现薄层厚度和超声纵波声速的同时表征。利用该方法对铝合金基体上的雷达吸波涂层（Radar Absorbing Coatings,RAC）进行实验测试及信号分析。结果表明：该方法可以有效实现混叠信号中超声特征参量的提取,反演得到吸波涂层厚度与千分尺测量厚度间相对误差为2.53%-3.72%、纵波声速测量相对误差为2.51%-3.75%。

For the overlapped signal and unknown longitudinal velocity leading to difficulty in measur-ing the thickness of thin layers, a method based on ultrasonic reflection coefficient amplitude spectrum （URCAS） matching analysis technique was proposed to characterize thickness and ultrasonic longitu-dinal velocity of thin layered structure simultaneously. An inverse algorithm based on the correlation coefficient method was introduced. The thickness and velocity were then determined by matching the theoretical and experimental URCAS within the effective frequency band of ultrasonic probe and inversing the ultrasonic testing parameters which corresponding to the maximum correlation coefficient. Experimental validation was conducted on the radar absorbing coatings （RAC） on the aluminum alloy substrates. The results show that this method can realize extraction of the ultrasonic parameters from the overlapped signal effectively, the relative errors between ultrasonic and micrometer measurement are in the range of 2. 53%-3. 72% for the thickness, and 2. 51 %-3. 75% for the longitudinal velocity.