## 4 Experiment
Wireless communication and MCRWPT technologies are adopted in the uniaxial rotation module to avoid cable winding and wear of slip ring. The MCRWPT system powers the load on the rotating unit, and the data of the inertial sensors (gyroscopes and accelerometers) is output to the upper computer through wireless communication. The maximum input voltage of the DC-DC converter used in the experiment is 40 V, and the output voltage is 5 V, so the ratio of \(V_{WPT}/V_{OUT}\) cannot exceed 8. When the  
Figure 14: The prototype of the uniaxial rotation module used the MCRWPT system. Figure 13: The main circuit components and parameters used in the experimental prototype. load resistance \(R_{OUT}\) is 2.5 \(\Omega\), the equivalent load resistance \(R_{L}\) is 160 \(\Omega\), calculated by Equation (11). When the output power is reduced to 1.6 mW, the load resistance is 15.625 k\(\Omega\), and the equivalent load resistance is 1 M\(\Omega\). When the load power is more than 1.6 mW and the output voltage is 5 V, the excitation frequency working range of the system can be obtained through the excitation frequency design method in Section 3.2.2. Considering that when the input voltage of the DC-DC converter is about 22.4 V, the output power is 10 W, and the equivalent load resistance of the system is calculated by Equation (11) to be 50 \(\Omega\). It is reasonable to choose 50 \(\Omega\) as equivalent load resistance in circuit design to analyze the characteristics of the circuit. System characteristic parameters include output voltage, output power, and TTE, and their relationship with excitation frequency is shown in Figure 15a. When the excitation frequency is 138.7 kHz, 143.35 kHz, and 145.3 kHz, the effective value of output power is 10 W, the output voltage of the MCRWPT system decreases, and the TTE increases gradually. The effectiveness of simulation analysis is verified. The excitation frequency is 145.3 kHz, and the output load voltage is 5 V. The output power varies with the load resistance. Furthermore, the TTE decreases with the decrease of output power, and the results are shown in Figure 15b, which is consistent with the simulation analysis. The output voltage ripple measured with an oscilloscope is shown in Figure 15c. The output voltage ripple is 34.75 mV, which is less than 50 mV, which meets the requirements of the inertial sensor for the supply voltage. Figure 15d shows the accelerometer data when the rotating unit rotates at a constant speed in the uniaxial rotation module. Experiments prove that the proposed MCRWPT method can be successfully applied to a uniaxial rotation module of a URMINS. At the same time, the effectiveness of the proposed design method is proved. The TTE of the MCRWPT systems is 74.6% at the output power of 10 W. The advantage of the approach in this article is that it is simple to  
Figure 15: (**a**) System characteristic parameters at different excitation frequencies measured by experiment; (**b**) The relationship between TTE and output power under \(f\) = 145.3 kHz; (**c**) The ripple of output load voltage; (**d**) An accelerometer’s measurement with the motor continuously rotating. implement and does not require any feedback. The shortcoming of this paper is that the PTE of the MCRWPT system gradually decreases with the decrease of the output power.