Guided wave (GW) plays an important role in nondestructive testing and structural health monitoring. In the general Lamb wave inspection, difference between the baselines and the measured signals are used for structural damage evaluation. However, the baselines are unavoidably influenced by operational and environmental conditions leads to an increased error during inspection. To deal with this issue, this paper presents a base-line free method based on the mode conversion and reciprocity principle of Lamb wave. Once the defect is asymmetrical with respect to the transducer pair (two identical piezoelectric transducers used as actuator and receiver respectively), the elastic wave path length of the converted mode will be different, resulting in failing of the reciprocity principle. By processing the signals received by the transducer pair and extracting the time parameters of the wave packets in mode conversion signals, the defect can be localized. Results from the signals generated by numerical simulation are presented to verify the feasibility of the method, and the effectiveness of the proposed baseline-free method is demonstrated with experimental results.

中文翻译：

---

基于模式转换和兰姆波互易原理的无基线缺陷定位方法

导波 (GW) 在无损检测和结构健康监测中发挥着重要作用。在一般的兰姆波检查中，基线和测量信号之间的差异用于结构损伤评估。然而，基线不可避免地受到操作和环境条件的影响，导致检查过程中的错误增加。针对这一问题，本文提出了一种基于兰姆波模式转换和互易原理的无基线方法。一旦缺陷相对于换能器对（两个相同的压电换能器分别用作执行器和接收器）不对称，转换模式的弹性波路径长度将不同，导致互易原理失效。通过对换能器对接收到的信号进行处理，提取模式转换信号中波包的时间参数，可以定位缺陷。给出了数值模拟产生的信号结果以验证该方法的可行性，并通过实验结果证明了所提出的无基线方法的有效性。