# Retractable Wireless Charging Windings for Inspection Robots
## 5 Results
Within the operational limits, including a constant resonant frequency, coupling coefficient, consistent parameters, and operating within the thermal range, the input voltage of 50 V is used to demonstrate the misalignment and energy efficiency of the SC-WPT. Figure 15a illustrates the lateral misalignment along the x-axis. The energy efficiency gradually increases as the Rx coil is repositioned laterally away from the Tx coil. The highest energy efficiency achieved is 77.11% at 0.7 m.  
Figure 14: Achieving transmitting power of 100 W using SC–WPT system over 1 m of distance. Figure 13: Waveforms from the experimental verification. Figure 15b shows the experiment conducted to observe the energy efficiency of the SC-WPT under angular misalignment conditions. The recorded data indicate a significant drop in energy efficiency as \(\alpha\) is gradually increased. The highest energy efficiency of 73.23% is observed at 0\({}^{\circ}\), while the lowest energy efficiency of 1.662% occurs when the Rx coil is rotated 90\({}^{\circ}\) about the z-axis. Table 5 summarizes the comparison between simulated and experimental results. The maximum output power shows a minor deviation of \(-\)1.27%, with the experimental value measured at 116.5 W and the simulated prediction at 118.0 W. This close match indicates that the simulation accurately captures the power transfer capability of the square coil winding under ideal and controlled conditions. Similarly, the peak energy efficiency yields a deviation of \(-\)2.39%, with experimental measurements reaching 68.72%, compared to a simulated maximum of 70.4%. These results confirm that losses introduced by non-idealities in real-world components such as switching inefficiencies, resistive losses in connectors, and measurement tolerances. It is reasonably low and does not substantially impair the overall system performance. At specific lateral offsets, the system also demonstrates consistency. At 0.6 m, the efficiency deviation is just +0.16%. This reflects a reasonable correlation between predicted and observed performance under spatial misalignment conditions. This is particularly significant in mobile robotics where consistent performance over variable coil alignment is critical for operational robustness. Finally, a more significant deviation of +16.06% is observed in the self-inductance of the receiver coil. This may result from differences in the construction tolerances, the coil sagging during deployment, or unaccounted-for electromagnetic interactions with nearby  
Figure 15: (a) \(\eta\) of lateral misalignment along the x–axis. (b) \(\eta\) of angular misalignment around the z–axis (distance from Tx to Rx = 1 m). \begin{table}
\begin{tabular}{c c c c} \hline
**Metric** & **Simulation Results 1** & **Experimental Results** & **Deviation (\%)** \\ \hline Max. Output Power (W) & 118.0 & 116.5 & \(-\)1.27 \\ Peak Energy Efficiency (\%) & 70.4 & 68.72 & \(-\)2.39 \\ Efficiency at 0.6 m Offset (\%) & 64.1 & 64.2 & +0.16 \\ Self-Inductance of Receiver (\(\mu\)H) & 74.71 & 86.70 & +16.06 \\ \hline \end{tabular}
\end{table} 
Table 5: Comparison between simulated and experimental results. metallic structures. The simulation assumes an ideal coil geometry with fixed winding positions, whereas the physical system involves a retractable frame subject to slight deformation, spacing variation, and parasitic coupling effects. These geometric factors can substantially impact inductance, especially in multi-turn, air-core coils. This small difference further supports the mechanical accuracy of the fabricated prototype and indicates that the retractable structure maintains a stable inductive profile during deployment.