## 6 Prototype and Experimental Setup  
A prototype was implemented based on the WPT and near-field communication components outlined in the previous sections. A system overview is shown in Figure 11. For the WPT part, both the primary and secondary sides are equipped with full-bridge circuits to provide the functionality of a bidirectional power transfer. The primary full bridge was implemented using four 600 V GaN FETs from Texas Instruments with part number LMG3422R030. The secondary full bridge is powered with four 650 V enhancement mode power transistors from GaN Systems, part number GS66508B. Using GaN technology, the inverter and rectifier have more potential to be downsized and can achieve lower hard switching losses than some conventional semiconductor technologies.  
The LCC compensation networks of both sides were implemented in Print Circuit Board (PCB), and the resulting values of each component are given in Table 2. Multilayer ceramic capacitors from TDK with C0G as dielectric elements were surface-mounted on the PCB. And ferrite cores with part number 495-5501-ND from TDK were used for the filter inductors \(L_{1f,2l}\).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Primary filter inductance \(L_{1f}\) & 12.22 \(\mu\)H \\ Secondary filter inductance \(L_{2f}\) & 7.99 \(\mu\)H \\ Primary filter capacitance \(C_{1f}\) & 288.87 nF \\ Secondary filter capacitance \(C_{2f}\) & 452.21 nF \\ Primary series capacitance \(C_{1s}\) & 123.75 nF \\ Secondary series capacitance \(C_{2s}\) & 193.29 nF \\ Primary coil inductance \(L_{1}\) & 40.39 \(\mu\)H \\ Secondary coil inductance \(L_{2}\) & 26.05 \(\mu\)H \\ Coupling factor at aligned position \(k_{\text{align}}\) & 0.21 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Values of compensation components and coil-system.  
Figure 11: The implemented test bench for a communication-based bidirectional WPT system.  
The coil system was designed according to the SAE J2954's Z1 class with a coil distance of about 130 mm. On top of the primary WPT coil and on the bottom of the secondary WPT coil, the communication coils were installed. Both communication coils were designed as double-D coils, as shown in Figure 6. The outside dimensions of the communication coils on both sides are about 28 mm \(\times\) 28 mm. Only one turn of winding was used for each coil. The position of the communication coil with reference to the WPT coil was adjusted so that the coupling between them was minimized. For the near-field communication, each side has an analog front end. An amplifier and filters were integrated into the PCB to protect the frequency band of communication from crosstalk due to the WPT. A non-inverting amplifier using LM7171 from Texas Instruments and ICL7662 from Analog Devices for dual supply were implemented. The secondary amplifier gain was configured at about 16 dB, the primary amplifier is about 0 dB, and the measured gain of the communication coil system in the frequency band is less than \(-\)16 dB. The transmitter signal, which is modulated on the secondary FPGA, is filtered and amplified via both amplifiers and finally received and demodulated via the primary FPGA. The FPGA board (DE10-Standard with Intel Cyclone(r) V SE 5 CSXFC6D6F31C6N) on each side is used for modulation and demodulation for the near-field-based communication, as well as the generation of control signals for the full bridge.