## 3 Methodology  
### Experimental Datasets  
In this paper, we utilize the datasets provided by the Open Guided Waves (OGW) platform [28]. Two carbon fibre plates having dimensions of 550 mm \(\times\) 550 mm and a thickness of 2 mm are used. The thickness of each layer within the plates is 0.125 mm. Prepreg material Hexply M21/34%/UD134/T700/300, a particular kind of carbon fibre prepreg material from Hexel\({}^{\text{\textregistered}}\), is used for the plates. A quasi-isotropic (QI) layup pattern is used to organize the layers within the plates, which means that the layers are angled differently to offer balanced strength in various directions. The omega stringer, a separate component, is also composed of Hexply M21/34%/UD194/T700/IMA-12K carbon fibre prepreg material. The stringer features a [45/0/90/45/90/45]S quasi-isotropic layup pattern. The nominal thickness of the stringer is 1.5 mm, and each layer within the stringer has a thickness of 0.125 mm. The complete experimental setup is given in Figure 6a.  
The plate has 12 piezoceramic transducers, surrounded by the stringer. These sensors are split evenly, with six on each side of the plate. Out of these sensors, six on one side act as actuators or exciters at a time, which are activated one by one, while the remaining 11 sensors receive the signals. So, each experiment collects a total of 66 separate signals from the decentralized and dispersed array of transducers' actuator-sensor pairs in a round-robin method, Figure 6b. The position of these transducers is given in Table 1.  
Figure 5: MODWT of damage Lamb wave signals.  
For anomaly detection, we consider 60 kHz Lamb wave excitation frequency. A Hann-windowed five-cycle excitation pulse was generated. For the measurement, the author of [28] considered seven different phases. For phase 1, five measurements were recorded on the pristine structure. In phase two, reference defects were attached to the plate at position \(D1\). An electromagnet with a metal block pressed the reference damage to the structure for maximum reliability. The electromagnet was then removed, leaving only the reference damage in contact with the structure. This process was repeated five times for each of the 13 damage sizes and positions. In the next phase, the author recorded another five baseline measurements after removing the reference damage. The author followed the same procedures for other damage positions in the next phases. Overall, 20 baseline and 520 damage measurements were recorded. Note that originally the author used three damage conditions present at different locations; however, in this study, we only considered two damage locations on the plate.  
The stringent significantly impacts guided wave propagation, resulting in considerable signal changes. Here, the real challenge is used for raw signals and to extract useful information related to the state of the structure. To simplify the analysis, we focus only on the signals that traverse the plate and are received by sensors on the opposite side. As a result, out of the total 66 signals, we narrowed our attention to 36 signal paths. Moreover, we considered only 2048 sampling points as we were interested in the first-arriving waves and reflections from the damage and stringer. There are 720 datasets, of which 90% were  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Transducer/Sensor ID** & **Coordinates** \\ \hline
1 & (450, 470) \\
2 & (370, 470) \\
3 & (290, 470) \\
4 & (210, 470) \\
5 & (130, 470) \\
6 & (50, 470) \\
7 & (450, 30) \\
8 & (370, 30) \\
9 & (290, 30) \\
10 & (210, 30) \\
11 & (130, 30) \\
12 & (50, 30) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Transducer/sensors position on pate.  
Figure 6: (**a**) Experimental Setup, (**b**) visualization of two damaged positions D1 and D2, and twelve transducers [28].  
used for the training purpose while 10% were used for validation. Some of the waveforms are given in Figure 7.