# A Novel Ropes-Driven Wideband Piezoelectric Vibration Energy Harvester
## 4 Results and Discussion
As shown in Figure 8, based on the structure of individual DB driving the GB, each of these three parameters has been investigated separately by keeping the other two parameters fixed. Figure 8a shows the output peak voltage against excitation frequencies from 40 to 55 Hz with different accelerations for a fixed rope margin (0.25 mm) and stiffness, result in the resonant frequency of 42.6 Hz. In fact, as the base acceleration increases from 0.4 g to 0.6 g, the output voltage and operating bandwidth of the GB increase, since the vibration amplitude of the DB increases. Likewise, for a fixed acceleration of 0.6 g and stiffness of 42.6 Hz, the frequency response with various rope margins is shown in Figure 8b. As can be seen, a lower rope margin results in a wider operating bandwidth at the expense of a reduction in the output voltage. Figure 8c plots the  
Figure 7: Normalized output power corresponding to individual and multi-LFDBs of novel VEH with optimal load resistance. frequency response with different frequency characteristic of the DB at an acceleration of 0.6 g and rope margin of 0.25 mm. It is seen that a lower stiffness of the DB results in a higher output voltage. Further, for a given acceleration, the extractable energy from the beam is inversely proportional to the resonance frequency [4]. Thus, the lower the frequency of the DB is, the higher the output voltage of the GB is. From the above results, it can be seen that the output and wideband behaviors of individual DB driving the HFGB are strengthened by an increase in the input acceleration and a decrease in the stiffness of the DB. There is a tradeoff for the rope margin, since it affects the frequency bandwidth and output behaviors with an opposite trend. As for the structure of multiple DBs driving the HFGB, naturally, the output and wideband behaviors are dependent on the parameters such as acceleration, rope margin, and stiffness of DBs. For example, for the structure of three DBs driving the HFGB, when the acceleration is changed from 0.2 g to 0.3 g (shown in Figure 9a) or the rope margin is adjusted from 2.0 mm to 0.5 mm (shown in Figure 9b), the output performance is improved during the joint frequency range of the DBs. Moreover, the smoother output and wideband behaviors can be achieved by the adjustment of rope margin and stiffness of LFDBs simultaneously at a fixed acceleration of 0.6 g, as shown in Figure 9c. Hence, it is possible to achieve a desirable performance for a given excitation by further optimizing parameters. In addition, due to the fact that there is no piezoelectric material attached to the driving beams, it allows more freedom for the design of the DBs--for example, the DBs can be designed as S-shaped beams, which is helpful to achieve a low-frequency wideband energy harvester [18; 34]. Figure 8: Parameters effects on the frequency response of the proposed wideband VEH system: (**a**) demonstrates the effects due to changing acceleration; (**b**) demonstrates the effects due to changing rope margin; (**c**) demonstrates the effects due to changing stiffness of the driving beam (DB).