## 2 Analysis of MCRWPT System for RMINS
### Characteristics of MCRWPT for the RMINS  
The MCRWPT system applied to power a single-axis RMINS is shown in Figure 4. The principle of the single-axis RMINS is that the motor drives the rotating unit to perform  
Figure 3: The relationship between output power and coupling coefficient.  
Figure 2: The relationship between output voltage, PTE and excitation frequency, equivalent load resistance, and coupling coefficient. (**a**) Output voltage changes with equivalent load resistance. (**b**) Output voltage changes with excitation frequency. (**c**) Output voltage changes with coupling coefficient. (**d**) PTE changes with equivalent load resistance. (**e**) PTE changes with excitation frequency. (**f**) PTE changes with coupling coefficient.  
periodic rotation to suppress the error from inertial sensors. The IMU mounted on the rotating unit is the load for the receiver of the MCRWPT system. The IMU consists of three gyroscopes, three accelerometers, and an information processing PCB, where the gyroscopes and accelerometers are mounted orthogonally. The transmitter and receiver form the MCRWPT system. Both the transmitter and receiver include corresponding PCBs and coils. The DC power supply powers the transmitter of the wireless power.  
According to the structure of the RMINS, the MCRWPT system needs to be designed and implemented with the following characteristics: First, the magnetic shielding structure is needed to reduce the leakage of the magnetic field because the inertial sensors and the framework are sensitive to the alternating magnetic field. Second, a suitable gap between the primary and secondary sides is needed due to the rotating unit's rotation. Third, the output voltage of the MCRWPT system is stable, and the output voltage ripple should be less than 50 mV. Otherwise, the accuracy of the inertial sensor will be affected. However, as the IMU operating time grows and the inertial sensor temperature gradually increases, the input power required by the IMU changes, causing a change in the output voltage in the MCRWPT system. Accordingly, the MCRWPT system reflects the following characteristics from the circuit principle in supplying power to the rotating unit of the RMINS.  
1. The coupling coefficient \(k\) is increased. Shielding the wireless power supply coil with soft magnetic material will increase the mutual inductance coupling coefficient k. Theoretical analysis shows that with the increase of \(k\), the efficiency of the MCRWPT system will increase, but the output power may decrease.
2. A variable load resistance exists in the MCRWPT system. The input power required by the IMU from startup to normal operation is different. With the increase in the working time of the RMINS, the temperature change will also affect the system's input power. This paper equates the change in input power to the change in load resistance since the input voltage is constant. Variable load resistance affects the output voltage and PTE.  
A simple design method for the MCRWPT system will be given in this paper, integrated with the above two points. This method focuses on the following two core issues in designing an MCRWPT system for an RMINS: (1) According to the structural characteristics of the RMINS system, the magnetic shielding structure of the wireless power supply coil is designed, and the magnetic leakage is analyzed. (2) The excitation frequency is designed to reduce the impact of load resistance changes on output voltage and PTE.