# Retractable Wireless Charging Windings for Inspection Robots
## 5 Results  
Figure 11a,b show the experimental results of energy efficiency during lateral and angular misalignment where the WPT system is operating in resonance frequency of 535 kHz and input voltage of 80 V. Figure 12a depicts the transmitted power when the half-bridge driver board is gradually supplied with input voltage up to 80 V. The Tx and Rx coils are tested with distance variations. The result shows the capability of the SC\(-\)WPT to transmit 35.76 W of power at a distance of 1 m apart from each coil. The highest transmitted power is when the distance is at 0.8 m (54.09 W). Figure 12b shows the corresponding output voltage measured across a load resistance of 10 \(\Omega\) with the highest at the distance of 0.8 m (32.4 V). These results validate the simulation conducted where the energy efficiency would be reduced significantly when lateral and angular misalignments are introduced between Tx and Rx coils. At 1 m of distance in terms of lateral misalignment, energy efficiency is recorded at 54.35%. Angular misalignment at 90\({}^{\circ}\) shows the lowest energy efficiency with 3.92%. Figure 10: Experimental setup using the half-bridge driver board connected to the SC\(-\)WPT system with a retractable Rx coil. The input voltage is gradually increased to achieve a level of transmitted power comparable to that of the octagonal coil WPT system [26]. Figure 13 shows the captured waveforms from the experimental verification, and Figure 14 illustrates the transmitted power as the input voltage is incrementally raised. The SC-WPT achieves an output power of 116.5 W when supplied with an input voltage of 140 V. The output voltage measured across the same load resistance of 10 \(\Omega\) is 45.38 V, with an energy efficiency of 68.72%. 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 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. The energy efficiency reported in this study refers to the end-to-end DC-to-DC efficiency of the WPT system. Specifically, it accounts for the total electrical power measured at the DC output of the rectifier (receiver side) relative to the DC input supplied to the inverter (transmitter side). This includes the losses associated with the inverter, coil coupling (AC-AC), and rectification stages. Measurements are performed using calibrated probes and oscilloscopes to capture RMS values at both the input and output sides, ensuring an accurate representation of the full-system efficiency. The input voltage is gradually increased to achieve a level of transmitted power comparable to that of the octagonal coil WPT system [26]. Figure 13 shows the captured waveforms from the experimental verification, and Figure 14 illustrates the transmitted power as the input voltage is incrementally raised. The SC-WPT achieves an output power of 116.5 W when supplied with an input voltage of 140 V. The output voltage measured across the same load resistance of 10 \(\Omega\) is 45.38 V, with an energy efficiency of 68.72%. Figure 12: (**a**) \(P_{out}\) from lateral misalignment along x–axis. (**b**) \(V_{out}\) from lateral misalignment along x–axis.