# Thermal-Mechanical Behaviour of Road-Embedded Wireless Charging Pads for EVs
## 9 Results
### Complete Pad Energized in Pavement  
In general, there was a good correlation between the predicted and measured temperatures in the embedded pad, although the predictions were not as close as for the suspended pad. Figure 18 shows the temperature on the top surface of the pavement and the flush mounted pad, with an ambient temperature of 50 \({}^{\circ}\)C. The predicted and measured distributions were similar, with the highest temperature on the surface radiating outward in an elliptical manner. The maximum measured and predicted temperatures on the surface differed by 3.7%. There was also a good correlation at the middle of the coil, where temperatures increased linearly. However, the increase in coil temperature with ambient temperature was noticeably higher in the simulations. Because of this, coil temperature was underpredicted by 9% at 13 \({}^{\circ}\)C ambient temperature and predicted almost exactly at 50 \({}^{\circ}\)C ambient temperature to be 99.8 \({}^{\circ}\)C.  
The temperatures on Ferrite 4 of the embedded pad are shown in Figure 19. As with the thermal results on the top surface and the coil, there was higher deviation between the measured and predicted temperatures in the ferrite, compared to those of the suspended pad. The gradient of simulated ferrite temperature with an increasing ambient temperature was also slightly higher than the measured gradient. Hence, the correlation was better at higher temperatures. The average deviation between measured and predicted temperature was 27% at 13 \({}^{\circ}\)C ambient temperature and 9% at 50 \({}^{\circ}\)C ambient temperature. Despite these larger differences, the 1-2 \({}^{\circ}\)C increase in temperature from the outside (Location A) to the inside (Location C) was still observed in both the experiment and simulations. Figure 18: (**a**) FE-predicted surface temperature of embedded pad inside environment at 50 \({}^{\circ}\)C. (**b**) Temperature measurement, using thermal camera, of the top pavement surface under the same conditions. The FE-predicted X-strain distributions on the ferrites in the embedded pad are presented in Figure 20. It is clear that the distribution of the embedded pad is significantly different to that of the unconstrained pad. Strains were still predominately in tension on top and compression on the bottom; however, because of the lateral constraints imposed by the pavement, the magnitude of the strains were highest closer to the outer edges (i.e., at Sensors 1A-4A). A snapshot of the predicted and measured strains is presented in Figure 21. Here, the results at 50 \({}^{\circ}\)C ambient temperature were omitted, due to irregularities in the recorded peaks of the FBG sensors, which may have occurred due to de-bonding between the pavement and pad. Looking at just the FEA results, it can be seen that, unlike all previous tests, strains did not increase linearly with temperature. The maximum predicted strains were similar in the embedded and suspended pads at 13 \({}^{\circ}\)C ambient temperature but, at 40 \({}^{\circ}\)C, the predicted strains of the embedded pad were around 50% lower. This non-linearity was due to the large change in the stiffness of embedment material with temperature, which significantly changed the pad boundary conditions. The presence of the pavement  
Figure 19: Comparison of measured and predicted temperatures on Ferrite 4 when the pad is embedded. Figure 20: FE-predicted X-strain distributions on ferrites in the embedded pad at 20 \({}^{\circ}\)C ambient temperature. (a) Top view. (b) bottom view. around the pad confined its thermal expansion, and therefore, slightly reduced the average magnitude of strains relative to the suspended condition. In general, there was a reasonable experimental-numerical correlation, in terms of both the change in strains with temperature and the change in strains along the ferrites. At 40 \({}^{\circ}\)C ambient temperature, the strain was underpredicted by 20% at 2A and overpredicted by 52% at 4A.