# Multi-Unit Coupled Motion Hybrid Generator Based on a Simple Pendulum Structure
## 3 Results and Discussion
### Structural Design and Optimization of MCM-HG  
Since the MCM-HG integrates eight power generation units with diverse output characteristics, it is necessary to study and optimize the structural parameters of each unit. To avoid the issues of large volume, heavy weight, and limited portability associated with traditional coils, specially designed spiral PCB coils were used in this study. The size of the PCB coils was determined to be 50 mm\(\times\)50 mm, and the output performance of the P-EMG unit was investigated for different numbers of turns, ranging from 100 to 500 turns in increments of 100 turns. Figure 2a shows the changes in voltage and current of the P-EMG unit under different numbers of turns. Given the same magnetic field variation, the open-circuit voltage and short-circuit current increase with the number of turns. For example, at 100 turns, the open-circuit voltage of the P-EMG is 0.11 V, and the short-circuit current is 1 mA. When the number of turns reaches 400, these values increase to 0.62 V and 2 mA, respectively. However, with a fixed size of the PCB coil, more turns result in finer wire diameters and smaller currents. At 500 turns, the values are only 0.2 V and 0.4 mA. Therefore, to ensure the best output performance of the P-EMG, the number of turns in the PCB coil was chosen to be 400. To validate the performance of the PCB coils, a linear motor was used to control the magnetic field variation and investigate the output performance. The experimental parameters were set as follows: acceleration range from 1.0 to 5.0 m/s\({}^{2}\) with an increment of 1.0 m/s\({}^{2}\); distance between the magnet and the PCB coil ranging from 1 to 9 cm with an increment of 2 cm. Figure 2b,c show the changes in voltage and current of the P-EMG unit. As the acceleration increases, the magnetic flux variation increases, and the output of the P-EMG also increases. The open-circuit voltage rises from 0.7 V to 2 V, and the short-circuit current increases from 0.22 mA to 0.62 mA. As the distance between the magnet and the PCB coil increases, the change in magnetic flux decreases, and the output of the P-EMG follows the same trend. The open-circuit voltage decreases from 1.2 V to 0.6 V, and the short-circuit current decreases from 0.37 mA to 0.19 mA as the distance increases from 1 cm to 9 cm. Considering the device design, an acceleration of 2 m/s\({}^{2}\) and a distance of 5 cm between the magnet and the PCB coil were selected to achieve optimal output performance. The swing of the simple pendulum significantly influences the output performance of the MCM-HG, making it essential to study and optimize the pendulum. Due to the track length limitation of the upper power generation units, the swing amplitude of the simple pendulum is fixed. Therefore, this paper only discusses the impact of the pendulum mass on the device output. Hollow trapezoidal acrylic structures were placed on both sides of the magnet block to expand the swing amplitude of the simple pendulum and serve as carriers for the counterweight blocks. As the mass of the simple pendulum increases from 110 g to 510 g, the force exerted on the S-TENG during swinging increases, and the contact between the friction layers becomes tighter. Consequently, the open-circuit voltage and short-circuit current of the S-TENG increase significantly, as shown in Figure 2d. However, when the pendulum mass increased from 410 g to 510 g, the improvement in S-TENG output performance was not significant. Moreover, the 510 g pendulum could not complete a reciprocating motion under the same excitation conditions due to its excessive mass. Therefore, we ultimately selected the 410 g pendulum. Additionally, for the S-TENG, the opening angle directly affects the output performance. If the angle is too small or too large, the S-TENG will not open fully, resulting in a significant reduction in electrical output. Therefore, this paper investigates the angle of the ramp that the S-TENG relies on.