基于宽频激励的管型结构导波检测

Pipe Structure Detection Based on Broadband Guided Wave Excitation

在对管型结构的导波检测过程中，需要预先选定导波模态，并确定激励频率，这个选择的过程存在一定的盲目性，而在多次反复试验中确定最佳激励模态和频率也会带来精力、时间、硬件资源的耗费问题。介绍一种信号处理方法，在宽频信号作为激励产生响应的基础上，采用该算法可获得其频带范围内任意单频激励信号对应的响应，有效解决了预先选定模态及频率的问题。同时，引入时频分析技术，根据缺陷反射回波能量的分布情况快速确定具有低模态转换响应的导波频率区间。通过对比各频率计算结果的模态和缺陷反射信号幅值，发现缺陷管中理想的激励导波频率在140～180 kHz，且缺陷反射回波幅值随激励信号周期增加而增加，但这种特点在低频表现得不明显。这为根据管中缺陷大小及类型，选择不同激励频率和周期提供了理论依据。

Pre-selecting mode and frequency of excitation signal is very important in guided wave inspection for pipe structures. The method by repeating trials to determine the optimum mode and frequency will enhance the consumption of energy, time and hardware resources. It shows a signal processing method to analysis the propagation property of various guided waves in pipes. Any response of single-frequency component contained in the broadband of the chirp signal could be obtained by this method. Simultaneously, the time-frequency analysis method is used to select the desired tone burst excitation through comparing the energy distribution of defect reflection signals. Verified by the finite element simulation, it is effective solution to find the guided wave that with lower mode conversion in propagation in pipe structures. After comparing the mode purity and the reflection amplitude, the results show that the frequency band between 140 kHz and 180 kHz is more suitable for using as excitation. In contrast to low frequency band, the reflection amplitude of signals obtained in this band increases along with the increase of excitation cycles. This provids a theoretical basis for the defects in accordance with the size and types chooses a suitable excitation frequency and period in nondestructive testing.