超声兰姆波的时频分析

声-超声方法在被测板件厚度较小时,板中传播的超声波模式主要是多模式的兰姆波。由于兰姆波的复杂性,声-超声方法回避了对信号进行进一步深入的分析,而采用所谓“应力波因子”对材料中能量耗散进行相对度量。当多模式与频散同时存在时,信号的识别异常困难,本文采用时-频分析的方法对声-超声信号进行了分离,只需一次测量就可满足分析要求。通过对兰姆波信号的伪Wigner-Ville分布进行时频重排和图像特征提取,能够精确地获得兰姆波的局部群速度频散曲线。

Time-frequency analysis of Lamb waves

It is multimode Lamb waves that compose the Acousto-ultrasonic (AU) signals when the thin plate is tested by AU method. Because of the complication of Lamb waves, AU method avoids the further analysis for signal components, and constructs so-called'Stress Wave Factor' instead to measure the dissipation of the energy. It is very hard to recognize the signals with both multiple modes and dispersion. In this paper, time-frequency analysis is used to separate the AU signals and only a single measurement is required. By combining the pseudo Wigner-Ville distribution with reassignment technique and feature extraction, portions of dispersion curves of Lamb waves can be obtained accurately.