中文摘要：

为了增加兰姆波测试信号特征提取的精度,降低噪声的影响,信号的预处理是必要的。本文采用一发一收兰姆波测试技术,在含有人工槽型缺陷的3mm厚铝板上进行了实验。选择带通无限长脉冲响应滤波器对兰姆波信号进行降噪。考虑到兰姆波的激发频率为250kHz,IIR滤波器的通带设置为160～330kHz。采用Hilbert变换获取滤波后信号的包络,结果显示,与滤波前兰姆波信号的包络相比,滤波后信号的包络更加平滑和清晰,各个波包的峰值可以唯一确定,为后续兰姆波信号的走时提取提供了方便。在此基础上,根据入射波与S0反射波峰值之间的时间间隔计算S0模式的群速度,结果与理论值较为接近,由此显示了滤波处理在兰姆波测试信号分析中的重要作用。

英文摘要：

In order to enhance the accuracy of feature extraction for Lamb wave test signal and to reduce the influence of noise in experiment,signal pre-processing is necessary.In this paper,an experiment was carried out in a 3mm thick aluminium plate with an artificial slot defect by using pitch-catch Lamb wave testing technique.A bandpass infinite impulse response（IIR） filter was selected for noise reduction of Lamb wave signal.Considering the excitation frequency of Lamb wave signal is 250kHz,the passband of IIR filter is set up at 160-330kHz.Hilbert transform was used to obtain the envelopes of filtered signal.Results show that in comparison with the envelope of unfiltered signal,the envelope of filtered signals are much smoother and clearer,and the peak of each wave packet can be uniquely determined,which are convenient for extraction of subsquent Lamb wave travel time.Moreover,the actual group velocity of S0 mode was consequently calculated by using the interval between incident wave and the peaks of reflected S0 wave.Obtained result is close to theoretical group velocity of S0 mode.Above results demonstrate the importance of filter processing in Lamb wave signal analysis.