## 5 Discussion  
A WPT generator coil produces a constant magnetic field if it is excited with a direct current. This field can be measured with chips currently available on the market, for example, QMC5883L [22]. Unfortunately, the field structure thus obtained does not correspond to the normal operating situation of the WPT, mainly due to the magnetic remanence of the ferrite.  
The compensation of the slow variations in the electromagnetic field due to the generator was achieved in [8] by measuring the field in a fixed position and applying the corrections accordingly. However, as we demonstrated in Section 3.5, for this purpose it is sufficient to measure the voltage excursion at the coil terminals. The obtained information is similar--for the specific case of the WPT field--to that generated by a separate sensor, with the advantage of methodical simplicity.  
The magnitude of the EMF intensity produced by the WPT depends on the supply current in the emitting coil. The field lines do not change. In other words, the \(H\) vector direction at any point in the near-WPT space (or the ratio of the vector projections on the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Measured Value** & **Measured Value** & **After Linearity Correction** & **After Geometrical Correction** \\ \hline WPT emitting coil voltage & 15,987 & 16,000 & 16,000 \\ X sensor coil & \(-2541\) & \(-2507\) & \(-244\) \\ Y sensor coil & 10,420 & 10,416 & 9886 \\ Z sensor coil & 25,798 & 24,976 & 24,475 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Measured values and their correction results.  
Figure 25: Magnetic field intensity vector map in a plane parallel to the emitting coil, 4 mm from the coil: (**a**) Y component; (**b**) Z component. The maximum value of the field corresponding to the reference was the value measured in the center of the coil. The X-direction component of the magnetic intensity vector had a similar evolution to that of the Y-direction component (and is not shown in the map). Different colors used to differentiate the x coordinate of the measured points.  
three orthogonal axes) does not change if the current excitation is different. Additionally, the ratio between the intensities of the EM field generated at any two points does not change.  
To conclude, to ascertain the spatial field configuration for a given excitation of a WP generator coil, it is enough that the ratios of the measured EMF values between adjacent points are correct.  
By applying the above corrections, the accuracy of the measured value ratios is ensured, provided that the currents in the WPT coil are correctly measured.  
Having obtained correct values, the measured EMF structure (the modulus, direction, and orientation of the EMF intensity vector at all points) corresponds to the real structure.  
Consequently, measurement validation with certified equipment (which, in fact, would only be used to confirm the ratios between intensities) is not necessary.  
In [4], the authors calculated the errors when measuring the electromagnetic field generated by a long line or two parallel lines. They demonstrated that by reducing the ratio between the radius of the sensor coil and the distance at which it was located, the errors were reduced. They concluded that these calculation methods could be adapted for other topologies.  
Our research aimed to measure the field generated by any WPT emitter coil, so the error calculation methods should be adapted for each case. However, for the sensor coil radius of 2.5 mm used herein and a WPT emitting coil with a radius of tens of millimeters, the errors estimated by [4] were less than 1%. Reducing the radius of the sensor coil unfortunately reduces the induced electromagnetic voltage, affecting the signal-to-noise ratio. That is why it will be necessary, in subsequent research, to improve the analog signal processing unit.