## 3 Finite Element Modeling and Probe Parameter Determination
### Determination of Probe Parameters
#### 3.2.2 Determination of Detection Coil Parameters  
The designed probe is aimed at detecting delamination with sizes ranging from 10 mm to 30 mm and thicknesses between 0.05 mm and 0.15 mm. This size range is commonly encountered for delamination, demonstrating a certain level of generality [31, 32]. Therefore, when determining the parameters of the detection coil, we chose to simulate the detection of a delamination with dimensions of 15 mm \(\times\) 15 mm \(\times\) 0.1 mm, which represents a size that is relatively central within the range. That means an alternating current is applied to the excitation coils with the parameter combination of \(D_{\rm e3}H_{\rm e3}K_{\rm e4}S_{\rm e1}\) in Table 2, and simulation \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Impact Factors** & **Level 1** & **Level 2** & **Level 3** & **Level 4** \\ \hline \(D_{\rm e}/\)mm & 2 & 4 & 6 & 8 \\ \(H_{\rm e}/\)mm & 0.6 & 0.8 & 1 & 1.2 \\ \(K_{\rm e}/\)mm & 0.6 & 0.8 & 1 & 1.2 \\ \(S_{\rm e}/\)mm & 1 & 2 & 3 & 4 \\ \hline \hline \end{tabular}  
To validate the rationality of the experiment, \(X\)e is chosen as the reference factor to conduct a 4-factor 4-level orthogonal experiment L16 (4\({}^{\rm t}\)), which requires a total of 16 trials. That is, simulation detection was carried out on the CFRP sample shown in Figure 5 under different parameter combinations of the excitation coils, analyzing and studying magnetic flux density at the point on the sample surface directly beneath the probe. The results are shown in Table 2.  
\end{table} 
Table 1: Factors and levels of orthogonal tests of excitation coils. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**NO.**} & \multicolumn{4}{c}{**Evaluated Parameters**} & **Reference** & **Results** \\ \cline{2-5}  & \(D_{\rm e}/\)mm & \(H_{\rm e}/\)mm & \(K_{\rm e}/\)mm & \(S_{\rm e}/\)mm & \(X_{\rm e}\) & \(B/\)T \\ \hline \#1 & 2 & 0.6 & 0.6 & 1 & \(X_{\rm e1}\) & 0.00593 \\ \#2 & 2 & 0.8 & 0.8 & 2 & \(X_{\rm e2}\) & 0.00765 \\ \#3 & 2 & 1 & 1 & 3 & \(X_{\rm e3}\) & 0.00772 \\ \#4 & 2 & 1.2 & 1.2 & 4 & \(X_{\rm e4}\) & 0.00308 \\ \#5 & 4 & 0.6 & 0.8 & 3 & \(X_{\rm e4}\) & 0.00836 \\ \#6 & 4 & 0.8 & 0.6 & 4 & \(X_{\rm e3}\) & 0.00437 \\ \#7 & 4 & 1 & 1.2 & 1 & \(X_{\rm e2}\) & 0.01468 \\ \#8 & 4 & 1.2 & 1 & 2 & \(X_{\rm e1}\) & 0.01538 \\ \#9 & 6 & 0.6 & 1 & 4 & \(X_{\rm e2}\) & 0.00669 \\ \#10 & 6 & 0.8 & 1.2 & 3 & \(X_{\rm e1}\) & 0.01538 \\ \#11 & 6 & 1 & 0.6 & 2 & \(X_{\rm e4}\) & 0.01227 \\ \#12 & 6 & 1.2 & 0.8 & 1 & \(X_{\rm e3}\) & 0.01474 \\ \#13 & 8 & 0.6 & 1.2 & 2 & \(X_{\rm e3}\) & 0.01156 \\ \#14 & 8 & 0.8 & 1 & 1 & \(X_{\rm e4}\) & 0.01361 \\ \#15 & 8 & 1 & 0.8 & 4 & \(X_{\rm e1}\) & 0.00956 \\ \#16 & 8 & 1.2 & 0.6 & 3 & \(X_{\rm e2}\) & 0.01054 \\ \hline \(A_{Z1}\) & 0.00609 & 0.00813 & 0.00828 & 0.01224 & 0.01156 \\ \(A_{Z2}\) & 0.01070 & 0.01025 & 0.01008 & 0.01171 & 0.00989 \\ \(A_{Z3}\) & 0.01227 & 0.01106 & 0.01085 & 0.01050 & 0.00960 \\ \(A_{Z4}\) & 0.01132 & 0.01094 & 0.01118 & 0.00592 & 0.00933 \\ \hline \(T_{Z}\) & 0.00617 & 0.00292 & 0.00289 & 0.00578 & 0.00167 \\ \hline \hline \end{tabular}  
\end{table} 
Table 2: Orthogonal experiment table for the excitation coils. detection is conducted on the CFRP sample as shown in Figure 5. The sample contains a delamination with dimensions of 15 mm \(\times\) 15 mm \(\times\) 0.1 mm. The study will investigate the impact of detection coil size on the rate of change in detection voltage. The factors that need to be determined for the detection coil are \(D_{\rm r}\), \(H_{\rm r}\), \(K_{\rm r}\), and \(N_{\rm r}\). Similar to the excitation coil, the detection coil also uses enameled wire with a diameter of 0.1 mm for winding.