## 6 Experimental Verification  
To verify the feasibility and effectiveness of the proposed topology and method, a SWIPT system with air gap of 10 cm and 60 W output power is constructed, as shown in Figure 12, The coupling coil disc has a diameter of 8 cm. There are four signal processing boards, two of them are signal transmitting boards, and the other two are signal receiving boards. The system is designed to achieve simultaneous bidirectional transmission of power and data through a shared channel. The system parameters are shown in Table 1.  
In order to verify the feasibility of circuit principle and control mode, the current and the voltage in the primary and secondary sides are measured in the process of the experiment. At the same time, for the information transfer, the information transmission at different frequencies and the simultaneous power and information transmission are also measured in the experimental processing, respectively. In order to verify the impact of the value of \(\alpha\), \(\beta\) and \(\phi\) in this SWIPT system, let \(\alpha=3\pi/4\) and \(\beta=5\pi/6\), \(\phi\) is switched between \(-\pi/2\) and \(\pi/2\). When \(V_{1}\) is 48 V, \(V_{2}\) is 30 V, and the output power is 60 W, Figure 13 shows the voltages and currents of the primary  
Figure 11: The schematic circuits of modulation and demodulation model. (**a**) Modulation circuit. (**b**) Forward information demodulation circuit. (**c**) Backward information demodulation circuit. and secondary sides in power transfer loop. Figure 13 displays the power transmitted from the primary side to the secondary side and Figure 13 is the backward power transfer. The voltages and the currents are in the same phase. Among them, \(V_{p}\) and \(V_{s}\) are output three-level square wave voltages of the primary side and secondary side. \(I_{p}\) and \(I_{s}\) output the sine wave currents on the primary side and the secondary side, respectively. From Figure 13,b, it can be seen that the voltage and current are in phase. Therefore, both forward and reverse power transmission are normal. In addition, the operating state of the system is resonant. When \(\alpha=\pi\) and \(\beta=\pi\), there are only two-level existed in the waveform of \(V_{p}\) and \(V_{s}\). If \(\alpha\
eq\pi\) and \(\beta\
eq\pi\), three-level waveforms appear. As shown in Figure 14, when the phase shift angle \(\phi\) between the primary and secondary bridge arms changes, the direction of power transmission also changes. When the phase shift angle \(\phi\) between the primary and secondary bridge arms changes from \(-\pi/2\) \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable** & **Value** & **Variable** & **Value** \\ \hline \(L_{1},L_{2}\) & 124 \(\mu\)H & \(L_{71}\)–\(L_{74}\) & 3 \(\mu\)H \\ \(C_{1},C_{2}\) & 250 nF & \(C_{41},C_{44}\) & 2.2 nF \\ \(R_{1},R_{2}\) & 0.05 \(\Omega\) & \(C_{42},C_{43}\) & 2.2 nF \\ \(f\) & 28.6 kHz & \(f_{dp}\) & 1.7 MHz \\ \(V_{1}\) & 48 V & \(f_{ds}\) & 1 MHz \\ \(V_{2}\) & 30 V & \(d\) & 10 cm \\ \(M\) & 36 \(\mu\)H & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of The Proposed WPT System. Figure 12: Experimental setup. Figure 13: Measured voltage and current waveforms of the primary and the secondary side during bidirectional power transfer. (**a**) Forward power transfer. (**b**) Backward power transfer. to \(\pi/2\), the direction of the output current I2 changes too. According to the experimental results, by changing the value of \(\phi\), the forward transmission of the power is changed to the reverse transmission, that is, the bidirectional transmission is completed, which verifies the previous theoretical analysis. Both the information modulation and demodulation cells are connected in series. The full-duplex information transfer adopts frequency shift keying (FSK) control method via a shared channel with power carrier. The signal extracted by the _LC_ frequency selection enters the high-pass filter or band-pass filter to remove the influence of the power carrier and other harmonics.