## 4 Results and Discussion
### Analysis of Output Voltage  
Figure 7 plots the variations in the voltage output of the \(PZT\) patch with respect to the excitation frequency at different embedment depths of \(PZT\) in the vertical direction (\(f\) = 10-50 Hz, \(H\) = 40 cm, \(h_{r}\) = 0.5-1). The variation in maximum output voltage at varied excitation frequencies is due to the displacement of granular soil. Compared with the other excitation frequency, it is found that maximum voltage output in the vertical direction was obtained for the depth ratio of 0.5 at resonance. Thus, a greater output voltage is obtained if the \(PZT\) patch is arranged at an appropriate depth from the surface of the granular soil. In other words, the \(PZT\) patch cannot be placed at a greater depth ratio and shallow depth in granular soils, as this reduces the voltage output efficiency. The efficiency of voltage output for the \(PZT\) patch embedded in a vertical direction at various excitations is shown in Table 6. The efficiency of the voltage output at varied excitation frequencies is analysed using the formula  
\[\left[\eta=\big{(}V_{f_{1}}-V_{f_{2}}\big{)}/\big{(}V_{f_{3}}\big{)}\right] \tag{11}\]  
where \(V_{f_{1}}\) is voltage output of \(PZT\) patch at 10 Hz frequency and \(V_{f_{2}}\) is the voltage output of the \(PZT\) patch at various frequencies (20-50 Hz). Figure 6: Cone resistance obtained from digital SCP data for confined granular fill with and without excitation frequency of (**A**) 10–30 Hz; (**B**) 40–50 Hz. \begin{table}
\begin{tabular}{c c c c} \hline
**Exciting Frequency (Hz)** & \(\alpha\) & \(\beta\) & \(\mathbf{R^{2}}\) \\ \hline
10 & \(-3\times 10^{-5}\) & 0.1157 & 0.9976 \\
20 & \(-3\times 10^{-5}\) & 0.1035 & 0.9988 \\
30 & \(-7\times 10^{-5}\) & 0.1539 & 0.9978 \\
40 & \(-6\times 10^{-5}\) & 0.1439 & 0.9946 \\
50 & \(-8\times 10^{-5}\) & 0.1432 & 0.9814 \\ \hline \end{tabular}
\end{table} 
Table 5: Fitting parameters \(\alpha\) and \(\beta\) for the confined granular fill at varying excitation frequency. Figure 8 shows the voltage output variation of the _PZT_ patch with respect to the excitation frequency at different embedment depths in the transverse direction (_f_ = 10-50 Hz, \(H\) = 40 cm, _h\({}_{r}\)_ = 0.5-1). This attempt was made to analyse the effect of vibration on _PZT_ patch embedded at a distance in lateral direction from the centreline. Table 6 shows the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Depth** & **Input Excitation** & **Voltage Output in** & **Efficiency (\%)** & **Voltage Output in the** & **Efficiency (\%)** \\
**Ratio (hr)** & **Frequency (Hz)** & **Vertical Direction (V\({}_{\textbf{v}}\))** & **Transverse Direction (V\({}_{\textbf{t}}\))** & **Efficiency (\%)** \\ \hline \multirow{4}{*}{0.5} & 10 & 2.6 & & 2.3 & \\  & 20 & 1.2 & 54 & 2.2 & 4.3 \\  & 30 & 1.7 & 35 & 2.4 & 4.3 \\  & 40 & 1.4 & 46 & 1.9 & 17.4 \\  & 50 & 2.1 & 19 & 2.2 & 4.3 \\ \hline \multirow{4}{*}{0.6} & 10 & 2 & & 2.4 & \\  & 20 & 1.1 & 45 & 1 & 58 \\  & 30 & 1.3 & 35 & 2.6 & 8 \\  & 40 & 1.3 & 35 & 0.9 & 63 \\  & 50 & 1.5 & 25 & 1.7 & 29 \\ \hline \multirow{4}{*}{0.7} & 10 & 2.4 & & 1.9 & \\  & 20 & 1.3 & 46 & 1.2 & 37 \\  & 30 & 1.1 & 54 & 1.5 & 21 \\  & 40 & 1.5 & 38 & 1.6 & 16 \\  & 50 & 1.7 & 29 & 1 & 47 \\ \hline \multirow{4}{*}{0.8} & 10 & 1.6 & & 2.4 & \\  & 20 & 1.5 & 6 & 2.8 & 17 \\  & 30 & 1.4 & 13 & 2.2 & 8 \\  & 40 & 2.3 & 44 & 2.3 & 4 \\  & 50 & 2.2 & 47 & 2 & 17 \\ \hline \multirow{4}{*}{1} & 10 & 3.2 & & 2.2 & \\  & 20 & 2.3 & 28 & 2.5 & 14 \\ \cline{1-1}  & 30 & 2.1 & 34 & 2.2 & 9 \\ \cline{1-1}  & 40 & 2.1 & 34 & 2.1 & 5 \\ \cline{1-1}  & 50 & 3.0 & 6 & 1.9 & 14 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Voltage output efficiency of _PZT_ patch embedded in poorly graded soil for various excitation frequencies. Figure 7: Output voltage for _PZT_ patches embedded at varying depths in the vertical direction. voltage output efficiencies of _PZT_ patches at various exciting frequencies embedded in a lateral direction.