# A Novel Piezoelectric Energy Harvester Using a Multi-Stepped Beam with Rectangular Cavities
## 5 Experimental Results and Discussion  
The harvester with the dimensions given in Tables 1-3 were fabricated and tested. The 2 mm thickness rectangular cavity in the center of the beam was formed by a wire cut EDM tool. To validate the analytical model and results, experimentation was conducted. A photograph of the experimental set up is shown in Figure 9. The function generator was used to apply the required input to the electromagnetic exciter and the output from the patches were observed using DSO (Agilent DSO1002A). The applied excitation signal had a 10 V peak-to-peak amplitude. The dimensions mentioned above were arrived at by simulation of the structure using COMSOL Multiphysics software.  
Initially the fabricated harvester was tuned to the first resonant frequency and the open circuit output voltage across the series connected piezoelectric patches were observed. Then, the load resistance was connected and the variation in load voltage with the variation in load resistance was measured. The same steps were repeated by making the harvester vibrate in the second mode frequency. The power was computed using Equation (43) for both the modes. Figure 10 shows a comparison between the harvester output with load in analytical and experimentation.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Proposed Harvester**} & \multicolumn{4}{c}{**First Mode**} & \multicolumn{4}{c}{**Second Mode**} \\ \cline{2-11}  & **F\({}_{1}\) (Hz)** & **V\({}_{0}\) (V)** & **R\({}_{\text{target}}\) (Kf)** & **V\({}_{\text{R}}\) (V)** & **P (mW)** & **F\({}_{2}\) (Hz)** & **V\({}_{0}\) (V)** & **R\({}_{\text{target}}\) (Kf)** & **V\({}_{\text{R}}\) (V)** & **P (mW)** \\ \hline with step and cavity & 21.02 & 61.55 & 181 & 34.46 & 6.6 & 35.58 & 48.85 & 122 & 27.69 & 6.13 \\ \hline with step and & 21.83 & 55.66 & 174 & 31.18 & 5.56 & 35.77 & 48.63 & 116 & 27.74 & 6.15 \\ \hline Conventional & & & & & & & & & & \\ \multicolumn{11}{c}{} & & & & & & & & & & \\ \multicolumn{11}{c}{} & & & & & & & & & & \\ \multicolumn{11}{c}{} & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Results from the analytical model.  
Figure 9: Photograph of the harvester; (**a**) multi stepped beam with cavity and (**b**) view of step with the cavity.  
Figure 10: Performance of the proposed energy harvester with variation in load resistance (analytical and experimental); (**a**) variation of voltage in the first mode, (**b**) variation of voltage in the second mode, (**c**) variation of power in the first mode and (**d**) variation of power in the second mode.  
Table 5 shows the comparison of the harvester's performance such as resonance frequency, open circuit output voltage, voltage across load resistance and the power obtained through experimentation and analytical modeling. In both the modes, the error computed was less than 5.47%. The results obtained from analytical modeling were in good agreement with experimentation. It was also validated in experimental investigation that the proposed harvester generated higher output wide operating frequency, that is, both in the first and second mode of vibration. Therefore, the energy harvester can be used to power self-sustainable consumer electronics, wireless sensor networks, industrial condition monitoring systems, etc.