## 3 Results
### Linearity Study and Distribution of Forces on the Platform  
Ten piezoelectric transducers, in a row on the platform, were employed to study the distribution of tread forces on the platform. The first piezoelectric corresponds to the heel area of the foot. The fifth piezoelectric corresponds to the arch of the foot. The seventh piezoelectric correspond to the metatarsal area and, finally, the tenth piezoelectric correspond to the tips of the toes (Figure 5).  
The difference in the voltage of each piezoelectric terminal was directly measured. An 80 kg person took five steps with each foot. The voltage generated by each piezoelectric is shown in Figure 6, and allows one to estimate the distribution of forces along the row of transducers. Figure 6 shows that, in this arrangement, the heel of the foot is the area that exerts the greatest pressure on transducers 1\({}^{\circ}\), 2\({}^{\circ}\), and 3\({}^{\circ}\), and, afterwards, the pressure is considerably reduced. The reduction of the output voltage is because this area coincides with the arch of the foot, or fascia; therefore, less pressure is exerted in this area. Then, there is a slight increase in the voltage of transducers 7\({}^{\circ}\) and 8\({}^{\circ}\), corresponding to the metatarsal part, and this exerts a slightly higher pressure.  
Figure 4: Output power of the platform for different piezoelectric transducers arrangement.  
Figure 5: Location of transducers in a row on the platform.  
Energy Harvested by the Platform with Lead Zirconate Titanate (PZT) Disks Considering Different Conditions  
The experiments were conducted considering different conditions to measure the energy harvested in real case studies. Three persons with different weights were employed for the platform experiments to check the influence of weight on the energy generation by the platform. The weights of each person were 85, 70, and 55 kg.  
Moreover, the platform was stepped on in three different positions, see Figure 7, to measure the effect of the footfall direction on power generation:  
* First Position: Standing with one foot on the vertical axis.
* Second Position: Standing with one foot on the horizontal axis.
* Third Position: Standing with one foot on the diagonal axis.  
Each test consists of a person stepping on the platform in a specific position. Then, the voltage in the capacitor is measured. Once the voltage of the capacitor is known, the energy stored in the capacitor is obtained by Equation (1). Table 4 shows the voltage generated by the platform by the footfall of persons with different weights and positions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Position**} & **Voltage (V) Generated** & **Voltage (V) Generated** & **Voltage (V) Generated** \\  & **by Person 1 (55 kg)** & **by Person 2 (70 kg)** & **by Person 3 (85 kg)** \\ \hline
1 & 5.16 & 8.805 & 12.508 \\
2 & 4.635 & 9.176 & 13.338 \\
3 & 4.861 & 8.953 & 13.134 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Output voltage generated by the footfall of different persons with different positions.  
Figure 6: Voltage of each piezoelectric in a row along a footprint.  
Figure 7: Step positions. 1 st Position (**left**); 2 nd Position (**center**); and 3 rd Position (**right**).  
Table 4 shows that the step does not have a great effect on the output voltage of the platform. However, the voltage generated by the platform is directly related to the weight according to Figure 8.  
The power generated by the platform in each step at the output of the rectifier can be obtained by Equation (2) and is shown in Table 5.