## 4 Experimental Verification and Discussion
### Voltage Response at Certain Rotation Speeds  
The simulation voltage response and the experimental voltage response were compared when the rotating speed was fixed. As Figures 19 and 20 show, the measured peak-to-peak values are slightly lower than the simulation results. The frequency of the simulated voltage is consistent with the frequency of the experimental voltage.  
Figure 19: Comparison of the simulated and experimental induced voltage response versus time in the coil when the Halbach array was applied at a gap diameter of 2 mm.  
Figure 18: Experiment on the voltage response at certain rotation speeds.  
The experimental data and the simulation data were compared at certain rotation speeds and the results are depicted in Figure 21. The RMS value of the induced voltage has a linear relationship with the rotation speed when the distance between the magnet and the coil is 2 mm. The RMS value of the induced voltage in the coil was the same when either of the two magnet arrays was applied in the REMEH.  
The RMS value of an induced voltage is an important indicator of energy conversion performance. The average power can be directly compared or calculated according to the RMS value of the induced voltage when the coil parameters are determined. The experimental results in Figure 22 show that the RMS value of the induced voltage in the coil of the REMEH using the two kinds of magnet array decreases as the gap increases at a rotation speed of 10 r/s. The advantages of using Halbach arrays in energy harvesting appear gradually as the gap increases. In the experiments, the RMS value of the voltage in the coils of the REMEH formed by the two-directional magnet array or the Halbach array is the same when the gap is 2 mm. The two-directional array has better performance when the gap is less than 2 mm and the Halbach array has better performance when the gap is greater than 2 mm. The simulation value of 1.55 mm and the experimental value  
Figure 21: Comparison of the simulation and experimental RMS value of the open-circuit voltage in the coil when the REMEH adopted the two kinds of arrays at a gap of 2 mm.  
Figure 20: Comparison of the simulated and experimental induced voltage response versus time in the coil when the two-directional array was applied at a gap diameter of 2 mm.  
of 2 mm exhibit a certain deviation, which is affected by multiple factors. The matching value of the gap diameter, which leads to the same RMS value of the voltage in the coil by the two kinds of magnet array, is determined by \(\Delta\)B. The number of magnetic poles of the Halbach array is half that of the two-directional array. Experiments show that although the magnetic flux intensity at the magnetic poles of the Halbach array is higher, the RMS value of the induced voltage in the coil with the two-directional array is larger at a small gap diameter, which is due to the faster change in magnetic flux. The gap between the 16 magnets, the coil, and the cubic magnets in the prototype has a certain deviation that was produced during assembly. In summary, the experimental data are in good agreement with the trend of the simulation data.