## 3 Results and Discussions
### Energy Harvesting Study
#### 3.3.2 Energy Harvesting Results  
During the energy harvesting studies, experimental measurements are taken to determine the electrical properties of porous EVA. To validate the proposed modeling approach provided in the preceding part, the three compositions are examined in order. More examples are provided to demonstrate the feasibility and usefulness of EVA porous piezoelectric polymers in the situation of complex mechanical conditions and realistic energy harvesting devices. Figures 8-10 present the evolution of the electrical parameters (current and voltage harvested) as a function of time according to the applied strain using the three compositions of EVA. After analyzing the figures, it is clear that the electrical parameter increases by increasing the rate of deformation. For example, to obtain a value of the recovered current of 371 pA, it is necessary to apply a deformation of 0.75% in the case of EVA 0%; on the other hand, for porous structures (EVA 37%), it suffices to apply only 0.25%. For a strain of 0.75%, we can obtain a current of 320 pA by the EVA 0% instead of 1027 pA by the EVA 37% or 1692 pA by the EVA 65%. These results clearly show that increasing the porosity represents one of the best solutions for improving the electromechanical conversion of polymers in the pseudo piezoelectric mode. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material Proprieties** & **EVA 0\%** & **EVA 37\%** & **EVA 65\%** \\ \hline Young Modulus (MPa) & 29 & 25 & 20 \\ Depolarization Temperature (\({}^{\circ}\)C) & 74 & 67 & 61 \\ Strain limit (\%) & 24 & 27 & 31 \\ Piezoelectric Coefficient d\({}_{33}\) (pC/N) & 2.2 & 4.2 & 5.1 \\ Time after deionization & 30 h & 33 days & 59 days \\ Relative Permitivity & 3.6 & 5.1 & 5.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Synthesis of materials’ physical properties. Figure 8: Electrical characteristics harvested by EVA 0% as a function of time under a transverse displacement with various values of strain \(S_{M}\). (**a**) current harvested with \(S_{M}\): 0.25%, (**b**) voltage harvested with \(S_{M}\): 0.25%, (**c**) current harvested with \(S_{M}\): 0.50%, (**d**) voltage harvested with \(S_{M}\): 0.50%, (**e**) current harvested with \(S_{M}\): 0.75%, (**f**) voltage harvested with \(S_{M}\): 0.75%. In the case of EVA 65%, the current delivered is well multiplied by a factor of 8 compared to EVA 0%. This suggests that the higher the porosity, the greater the current that can be harvested. The results obtained clearly show that increased strain has a remarkable influence on the voltage and current in the case of porous piezoelectric materials. The properties of the internal gas of porous films directly influence the electrical properties. Figure 11 illustrates the dependence of current and voltage harvested using three compositions of porous EVA. The simulation behavior predicted by the proposed model  
Figure 10: Electrical characteristics harvested by EVA 65% as a function of time under a transverse displacement with various values of strain \(S_{M}\). (**a**) current harvested with \(S_{M}\): 0.25%, (**b**) voltage harvested with \(S_{M}\): 0.25%, (**c**) current harvested with \(S_{M}\): 0.50%, (**d**) voltage harvested with \(S_{M}\): 0.50%, (**e**) current harvested with \(S_{M}\): 0.75%, (**f**) voltage harvested with \(S_{M}\): 0.75%. Figure 9: Electrical characteristics harvested by EVA 37% as a function of time under a transverse displacement with various values of strain \(S_{M}\). (**a**) current harvested with \(S_{M}\): 0.25%, (**b**) voltage harvested with \(S_{M}\): 0.25%, (**c**) current harvested with \(S_{M}\): 0.50%, (**d**) voltage harvested with \(S_{M}\): 0.50%, (**e**) current harvested with \(S_{M}\): 0.75%. Equation (12) has been compared with the experimental setup of the power harvested by cellular polymers. In this figure, the points present the experimental results, and the curve presents the developed theoretical model.