## 4 The Scanning Procedure  
All the practical experiments were performed with the 3D scanner prototype in Figure 22.  
This system helped obtain, process, and view the voltage signal delivered by the 3D sensor coil. The analog processing of the signals from the coil was carried out in the analog signal processing unit, realized with the following integrated circuits: AD823 [20] for amplification and filtering, 4052 [21] for analog multiplexing, and AD636 [18] for rms-to-dc conversion. The circuit diagrams used were typical, presented in the application notes of the manufacturer. The full circuit diagram of the analog signal measuring path is shown in Appendix A, Figure A1.  
The excitation signal supplied to the WPT emitting coil came from a Protek 9305 sinusoidal generator with 20 VPP voltage and 150 kHz frequency.  
Obtaining data according to the spatial distribution of the scanned EMF involved implementing three tasks:  
1. The preliminary calibration of the measuring system, which included measuring the deviations from the normal directions at the three coil surfaces related to the orthogonal directions represented in Cartesian coordinates, and balancing the signal amplifications (i.e., corresponding to the three orthogonal directions).
2. Performing the measurement of the EMF, which included positioning the 3D field sensor, measuring the induced EMV in the three coils of the sensor, and measuring the WPT emitting coil voltage.  
Figure 21: (a) Error diagram of EMF strength; (b) error diagram of EMF direction.  
Figure 22: Setup of the 3D scanning system: (a) block diagram; (b) bench setup. Here, (1) WPT emitting coil; (2) 3D sensor coil; (3) CNC mechanical arm; (4) analog signal processing unit (5) ADC and controller; (6) generator; (7) CNC driver; (8) power supply; (9) general controlling laptop.  
Making corrections to the measured values (in this work, the corrections were made using software at the end of the scanning process), which included the following for each scanned point--correcting the linearity/slow variations and performing a geometric correction.  
The specific procedure for the spatial measurement of the field followed the chart in Figure 23.  
To exemplify the scanning and correction operations, we used a WPT emitting coil with the following nominal parameters:  
* Inductance: L = 19.5 \(\mu\)H at 125 kHz.
* Q factor: Q = typ. 220 at 125 kHz.
* Rated current: IR = 9.5 A at \(\Delta\)T = 400.
* DC resistance: RDC = typ. 35 m \(\Omega\) at 20 \({}^{\circ}\)C.
* Self-resonant frequency: SRF = 5 MHz.  
The measured values and their corrections for a random point extracted in the space near to the WPT (Figure 24) are shown in Table 1.  
Figure 23: Flowchart of spatial measurement procedure: (**a**) preliminary calibration; (**b**) scanning process; (**c**) corrections.  
Figure 24: The point at which vector \(H\) was measured.  
A reference value (representing the measured output generator voltage) of 16,000 was used for slow variation compensation. We noticed that, following the geometric correction, the value for the X direction became about 0.1% of the Z-direction value, which confirmed the requirement of this correction (see the random point position in the figure).  
Pertaining to the grid density, we took measurements every 2 mm in the half-space above the ferrite base, totalling 106,641 points considered. The results are shown in Figure 25.