## 4 Simulation Analysis of the Designed Probes
### Comparison Analysis of Different Probes  
Figure 18 shows two commonly used probes for CFRP eddy current testing: the single pancake probe and the single rectangular probe. In the simulation experiments, these two probes, along with the designed probe, were used to detect the delamination in the CFRP sample (Figure 5). The dimensions and number of turns of the three probe excitation coils are the same. Figure 19 shows the detection voltage difference signals obtained by the three probes as they scanned the CFRP sample along the scanning path illustrated in Figure 7. The sample contains a delamination with dimensions of 15 mm \(\times\) 15 mm \(\times\) 0.1 mm.  
From Figure 19, it can be seen that the designed probe has a detection voltage difference peak of 0.3324 V. The detection voltage difference for the single rectangular probe is 0.2266 V, which is only 68% of the designed probe's detection voltage difference. The detection voltage difference peak for the single pancake probe is 0.2095 V, which is only 64% of the designed probe's detection voltage difference. It is evident that the designed probe has a larger detection voltage difference peak, making the detection signal less susceptible to being overwhelmed by noise in actual testing. When the dimensions and number of turns of the excitation coils for the three types of probes are the same, the designed probe exhibits stronger detection capability compared with the single rectangular and single pancake probes.  
In order to visually compare the sensitivity of the three probes, each probe was used to simulate the detection of three different dimensions of delamination in the CFRP sample shown in Figure 5 (15 mm \(\times\) 15 mm \(\times\) 0.1 mm, 15 mm \(\times\) 15 mm \(\times\) 0.05 mm, and 10 mm \(\times\) 10 mm \(\times\) 0.05 mm). Calculate the changes in the detection voltage difference peak (\(V_{\text{peak}}\)) of the three probes with the changes in delamination lateral dimension (\(d\)) and delamination thickness (\(l\)). This calculation involves an approximate slope calculation:  
\[Sensitivity1 = \frac{\Delta V_{\text{peak}}}{\Delta d} \tag{14}\] \[Sensitivity2 = \frac{\Delta V_{\text{peak}}}{\Delta l} \tag{15}\]  
Figure 19: Detection voltage differences for different probes.  
Figure 18: CFRP eddy current testing commonly used probe: (**a**) single pancake probe; (**b**) single rectangular probe.  
The calculation results from Equation (14) reflect the sensitivity of the probe to changes in delamination lateral dimension, while the results from Equation (15) reflect the sensitivity of the probe to changes in delamination thickness. Through these calculations, the sensitivity of the probe can be comprehensively evaluated [36]. Table 9 presents the sensitivities of the three probes.  
According to the results in Table 11, when the dimensions and number of turns of the excitation coils for the three types of probes are the same, the novel triple rectangular coil probe exhibits higher detection sensitivity for the defects set in the simulation experiment. When the lateral dimension of delamination changes by 5 mm, the sensitivity of the single pancake probe and the single rectangular coil probe is only 88.24% and 72.55% of that of the novel triple rectangular coil probe. Additionally, the novel triple rectangular coil probe is more sensitive to changes in delamination thickness. When the delamination thickness changes by 0.5 mm, the sensitivity of the single pancake probe and the single rectangular coil probe is only 49.04% and 56.69% of that of the novel triple rectangular probe.