## 7 Experimental Results  
In this section, the proposed combined information and power transfer system is verified. The WPT transmitter DC voltage is provided by an EA-PS8500-60 power supply. The WPT receiver is terminated on an electronic-load EA-ELR 9750-22. The waves of the WPT and near-field communication were acquired using a Yokogawa DLM4038 oscilloscope. The forward and reverse WPT modes are presented in Figure 12. On the left side, an overview of the NFC transmitter and receiver signals, as well as the WPT voltage and current waves for the forward power transfer, are given. The WPT primary side was synchronized using the communication signal transmitted from the secondary side to the primary side. The primary voltage phase was adjusted about 90\({}^{\circ}\) ahead of the secondary phase for the forward power transfer. The primary parameters (the phase and the duty cycle) were extracted from the communication data packages. On the right side of the figure, the primary voltage phase was set to about 90\({}^{\circ}\) behind the secondary phase; thus, the phase difference of the secondary voltage current was about 180\({}^{\circ}\) shifted. Therefore, the power direction was reversed. Figure 13 shows the measured crosstalk at the WPT power of 700 watts. The receiver signal is acquired without a transmitter signal, the external  
Figure 12: Left side: WPT waves and communication signals of the forward WPT; right side: reversed WPT. applied to the inverter and rectifier, and both operate at a full duty cycle, so pure noise from the WPT system is recorded. As shown in the right figure, the crosstalk magnitudes in the communication frequency band are low, so the communication is well protected. However, with significantly increased WPT power, the crosstalk magnitudes will further increase, which could lead to an error in communication. One potential solution is to reduce the number of subcarriers so the amplitudes of each of the subcarriers can be sufficiently higher than the amplitudes of the crosstalk; therefore, the communication is robust. Besides the signal overview for the aligned position, the effects that resulted from misalignment (a position offset between the primary and secondary coils) are presented in Figure 14. As shown in Figure 14a, due to misalignment in the x and y directions, a sin-wave due to the WPT fundamental was overlaid on the receiver signal (third row). The overlaid noise was well suppressed via the digital filter implemented in the FPGA, and the filtered signal is shown in the second row of Figure 14b1. It ensures that the auto-correlation result not be affected (third row); thus, the synchronization is precise and robust in misaligned positions. Figure 14: The receiver signal with an overlaid WPT fundamental due to misalignment @\(\Delta x\approx 10\) cm and \(\Delta y\approx 10\) cm. **(a)** Measured waves at the misaligned position. **(b.1)** The overlaid WPT fundamental is filtered via the digital filter implemented in the FPGA. The synchronization is generated based on the calculation in (34), and the position is determined as shown in Figure 9. **(b.2)** shows the frequency response of the 150 th-order filter. **(c.1,c.2)** show the indexes, amplitudes, and phases of subcarriers from demodulation signal taps and theory, respectively. Figure 13: The crosstalk from the WPT is measured at the communication receiver. The left side shows the overlaid fundamental and high-frequency oscillation due to MOSFETs switching in the time domain. The right side shows the wavelet verification of the receiver signal with crosstalk, the fundamental noise, and the high-frequency oscillation located outside the communication frequency band. A fixed-point digital bandpass filter with a 150 th order was implemented in the FPGA, and the frequency response is presented in Figure 13(b). The cutoff frequencies are set based on the subcarrier frequencies. In Figure 13(c), four subcarriers with indexes 5, 6, 7, and 8 (frequencies of 1.96, 2.34, 2.73, and 3.13 MHz) from the FPGA signal taps are presented.