## 4 Results and Discussions
### PAUT Guided Wave Method
Table 5 shows the results of PAUT guided wave signal parameters for the CFRP sample. In Table 5, the arrival time of the reflection signal from the plate edge and the defect (hole) are presented (See Figure 2 for reference). The difference between the arrival times from the plate edge and from the defect (hole) was calculated. Considering the wave velocity, which was experimentally determined in a previous work [8], the distance between the plate edge and defect (hole) was determined experimentally. Comparing the distance between the plate and the defect (hole) which was determined experimentally with the actual location (as designed = 30 mm) shows that the location of the defect (hole) can be determined using the proposed technique within an acceptable range. When the size of the defect (hole) is larger, there is a better probability of detection, and the accuracy in determining the location of the defect (hole) is higher. In addition, when there is less interference between wave modes, such as in the case of larger distances, there is higher accuracy of detection. Better accuracy at larger distances occurs because, when the travelling distance for the guided waves is short, these wave modes are not stabilized and have many overlaps and low signal-to-noise ratio which cause higher inaccuracy. Figure 11 shows a typical signal for the experimental result listed in Table 5 for CFRP. Figure 12 shows the change in signal amplitude at different defect (hole) sizes for the experiments in Table 5 for CFRP. The amplitude of the signal from the plate edge is inversely proportional to the hole diameter. However, the amplitude of the signal from the hole is directly proportional to the hole diameter. As the hole diameter increases (i.e., larger defect), a larger part of the ultrasonic energy is reflected by the defect (hole), and consequently a smaller part will hit the edge. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{6}{c}{**Experimental Setup Parameters for PAUT Guided Wave Inspection of CFRP**} \\ \hline \multirow{2}{*}{**Frequency (MHz)**} & **Thickness** & \multirow{2}{*}{**Gain (dB)**} & **Element Qty.1** & \multirow{2}{*}{_fd2_} & **Element** \\  & & **(mm)** & & & & **Step3** \\ \hline
1.5 & 1 & 35 & 4 & 1.5 & 1 \\ \hline \multicolumn{6}{c}{1 Number of active elements at each sequence in phased array ultrasound transducer} \\ \multicolumn{6}{c}{2 frequency \(\times\) plate thickness (MHz.mm)} \\ \multicolumn{6}{c}{3 Incremental steps in terms of number of elements at each sequence} \\ \hline \hline \multicolumn{6}{c}{**Defect Detection Signal Characteristics**} \\ \hline \multirow{2}{*}{**Experimental Trial \#**} & **Hole** & \multirow{2}{*}{**Diameter(mm)**} & **Signal** & **Distance of** & **Arrival Time** & **(us) (Edge/Hole)** & **D\({}_{\text{Time}}\)** & **D\({}_{\text{dist}}\)** \\  & & & **Edge(mm)** & **Edge** & **Hole** & **(us)** & **(mm)** \\ \hline
**1** & & Edge/Hole & 50 & 25.64 & 13.81 & 11.83 & 48.9 \\ \hline
**2** & & Edge/Hole & 100 & 35.6 & 24.54 & 11.06 & 45.7 \\ \hline
**3** & & Edge/Hole & 150 & 46.11 & 37.08 & 9.03 & 37.3 \\ \hline
**1** & & Edge/Hole & 50 & 26.76 & 14.07 & 12.69 & 52.5 \\ \hline
**2** & **1** & Edge/Hole & 100 & 35.62 & 26.11 & 9.51 & 39.3 \\ \hline
**3** & & Edge/Hole & 150 & 45.97 & 37.28 & 8.69 & 35.9 \\ \hline
**1** & & Edge/Hole & 50 & 24.52 & 14.11 & 10.41 & 43.0 \\ \hline
**2** & & Edge/Hole & 100 & 36.24 & 26.89 & 9.35 & 38.6 \\ \hline
**3** & & Edge/Hole & 150 & 46.25 & 37.36 & 8.89 & 36.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Signal parameters for flaw detection for CFRP.