## 3 Experimental Setup
In addition, the durability of the sensor was also studied. Three more loading-unloading rounds were carried out at 12, 24, and 48 h after the first round. Experimental data are shown in Table 2 and Figure 1:6 \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Interval** \\ **Time (h)** \\ \end{tabular} } & \multirow{2}{*}{**Force/N**} & \multicolumn{2}{c}{**Left Peak (\(\mathrm{\lambda_{L}}\))/nm**} & \multicolumn{2}{c}{**Split Point (\(\mathrm{\lambda_{S}}\))/nm**} & \multicolumn{2}{c}{**Right Peak (\(\mathrm{\lambda_{R}}\))/nm**} \\ \cline{3-8}  & & **Loading** & **Unloading** & **Loading** & **Unloading** & **Loading** & **Unloading** \\ \hline \multirow{8}{*}{12} & 4.0 & 1546.424 & 1546.444 & 1546.596 & 1546.636 & 1546.716 & 1546.752 \\  & 4.5 & 1546.424 & 1546.442 & 1546.596 & 1546.644 & 1546.732 & 1546.784 \\  & 5.0 & 1546.420 & 1546.440 & 1546.604 & 1546.652 & 1546.748 & 1546.808 \\  & 5.5 & 1546.416 & 1546.438 & 1546.612 & 1546.656 & 1546.764 & 1546.848 \\  & 6.0 & 1546.416 & 1546.438 & 1546.624 & 1546.662 & 1546.796 & 1546.852 \\  & 6.5 & 1546.412 & 1546.436 & 1546.628 & 1546.678 & 1546.812 & 1546.868 \\  & 7.0 & 1546.420 & 1546.436 & 1546.652 & 1546.692 & 1546.864 & 1546.884 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental results of local lateral forces and left peak, split point, and right peak wavelengths for the FBG under different time intervals. Figure 12: Residual distribution of wavelength drift: (**a**) split point, (**b**) right peak. The sensitivities are recorded in Table 3, and residual distribution is shown in Figure 14. It can be noted that there is a slight yet acceptable fluctuation, meaning that the sensing capability will not degrade over time. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Interval** \\ **Time (h)** \\ \end{tabular} } & \multirow{2}{*}{**Force/N**} & \multicolumn{2}{c}{**Left Peak (\(\lambda_{\text{L}}\))/nm**} & \multicolumn{2}{c}{**Split Point (\(\lambda_{\text{S}}\))/nm**} & \multicolumn{2}{c}{**Right Peak (\(\lambda_{\text{R}}\))/nm**} \\ \cline{3-8}  & & **Loading** & **Unloading** & **Loading** & **Unloading** & **Loading** & **Unloading** \\ \hline \multirow{8}{*}{24} & 4.0 & 1546.428 & 1546.428 & 1546.596 & 1546.596 & 1546.696 & 1546.716 \\  & 4.5 & 1546.426 & 1546.424 & 1546.600 & 1546.602 & 1546.728 & 1546.728 \\  & 5.0 & 1546.426 & 1546.424 & 1546.604 & 1546.606 & 1546.744 & 1546.744 \\  & 5.5 & 1546.422 & 1546.426 & 1546.612 & 1546.612 & 1546.756 & 1546.764 \\  & 6.0 & 1546.422 & 1546.426 & 1546.624 & 1546.624 & 1546.780 & 1546.792 \\  & 6.5 & 1546.422 & 1546.422 & 1546.632 & 1546.628 & 1546.808 & 1546.812 \\  & 7.0 & 1546.424 & 1546.424 & 1546.632 & 1546.632 & 1546.824 & 1546.822 \\ \hline \multirow{8}{*}{48} & 4.0 & 1546.431 & 1546.424 & 1546.604 & 1546.600 & 1546.724 & 1546.718 \\  & 4.5 & 1546.424 & 1546.426 & 1546.598 & 1546.602 & 1546.739 & 1546.738 \\  & 5.0 & 1546.429 & 1546.426 & 1546.609 & 1546.611 & 1546.753 & 1546.755 \\  & 5.5 & 1546.425 & 1546.423 & 1546.614 & 1546.619 & 1546.772 & 1546.771 \\  & 6.0 & 1546.417 & 1546.417 & 1546.625 & 1546.627 & 1546.805 & 1546.799 \\  & 6.5 & 1546.412 & 1546.420 & 1546.632 & 1546.629 & 1546.813 & 1546.818 \\  & 7.0 & 1546.422 & 1546.427 & 1546.653 & 1546.652 & 1546.867 & 1546.866 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 13: Response curve of wavelength variation of \(\Delta\lambda_{\text{L}}\), \(\Delta\lambda_{\text{S}}\) and \(\Delta\lambda_{\text{R}}\) for the FBG relative to force variation at the given time intervals: (**a**) loading–12 h, (**b**) unloading–12 h, (**c**) loading–24 h, (**d**) unloading–24 h, (**e**) loading–48 h, (**f**) unloading–48 h.