# Experiment Investigation of Bistable Vibration Energy Harvesting with Random Wave Environment
## 4 Discussion
### Effect of Amplitude of Periodic Excitation Signal  
In order to generate the stochastic resonance, it is necessary to vibrate with the periodic signal by the mini shaker, however, periodic excitation signals exist in nature and do not necessarily have to be artificially shown in the research results of the literature. In order to investigate the effect of frequency and amplitude on the initial stage of the study, this paper has given a periodic excitation signal using a mini shaker.  
In the previous section, the effect of the frequency of the periodic excitation signal on the stochastic excitation was examined by the measurement experiment; here, in order to examine the effect of the amplitude of the periodic excitation signal, the response vibration of the mass block is set to 0.45 Hz from the most intense frequency, the amplitude is set to 15 mm, 20 mm, and 25 mm, respectively, and the excitation experiment is performed; the measured results are shown in Figures 18-20.  
Figure 19: Measurement results of response vibration displacement and vibration power generation when vibrating with a random signal and a period signal 0.45 Hz of middle amplitude 20 mm. (**a**) Results of response vibration displacement. (**b**) Diagram of displacement velocity of vibration of the support. (**c**) Diagram of displacement velocity of vibration of the mass block.  
Figure 18: Measurement results of response vibration displacement and vibration power generation when vibrating with a random signal and a period signal 0.45 Hz of small amplitude 15 mm. (**a**) Results of response vibration displacement. (**b**) Diagram of displacement velocity of vibration of the support. (**c**) Diagram of displacement velocity of vibration of the mass block.  
In the figure, if the excitation frequency is set correctly, regardless of the amplitude, the resonant resonance is generated in the case of three amplitude excitation. The correlation between response vibration displacement and velocity graph is compared, when the amplitude of the periodic excitation signal is different, the maximum speed of the response vibration of the support stage tends to be a little larger, and the maximum speed of the response vibration of the mass block also becomes larger as the amplitude increases. Moreover, in the three excitation cases, the response vibration of the mass block clearly shows the bistable vibration across both sides of the vibration model, and the stochastic resonance phenomenon is generated.  
However, it can be confirmed that the voltage value of the generated vibration power generation is changed slightly by the difference in the amplitude of the periodic excitation signal. The average voltage value at a small amplitude of 15 mm is 3.27 V, the maximum voltage value is 12.19 V, the average voltage value at the middle amplitude of 20 mm is 3.28 V, the maximum voltage value is 16.63 V, the average voltage value at 25 mm of the large amplitude is 4.17 V, and the maximum voltage value is 16.29 V.  
The results of calculating the average electric power are summarized in Figure 21. As shown in Figure 21, by increasing the amplitude of the periodic excitation signal, the average electric power obtained can be confirmed to be a little larger. Therefore, it is possible to confirm that the amplification effect which changes from the single stable vibration state to the bistable vibration state is large, and that the vibration generation quantity using the amplification effect is larger than the pursuit of the vibration generation quantity by simply increasing the vibration amplitude.  
Figure 21: Results of comparing average electrical power with different amplitude.  
Figure 20: Measurement results of response vibration displacement and vibration power generation when vibrating with a random signal and a period signal 0.45 Hz of large amplitude 25 mm. (**a**) Results of response vibration displacement. (**b**) Diagram of displacement velocity of vibration of the support. (**c**) Diagram of displacement velocity of vibration of the mass block.