## 5 Experimental Results and Discussion
### Experiments of 2# Piezolectric Brick  
The experiment arrangement for this section is as below: firstly, 2#1 and 2#3 PZT4 patches were pasted tightly on upper surfaces of PCS1 and PCS2 shown as Figure 2, and tests about the output voltages/average powers from 2#1 and 2#3 PZT4 patches were conducted by considering changes of the force arm length, amplitude and frequency of footstep excitation (_f_ = 1 Hz/2 Hz), and the load resistance; secondly, 2#2 and 2#4 PZT patches, same as 2#1 and 2#3, were pasted on lower surfaces of PCS1 and PCS2, and the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Amplitude of Footstep Excitation/N** & **250** & **300** & **350** & **400** & **450** & **500** \\ \hline
19.5 mm & 32 & 41 & 54 & 61 & 68 & 77 \\
1\#1 unimorph & 26.5 mm & 60 & 81 & 96 & 107 & 117 & 131 \\
33.5 mm & 118 & 133 & 155 & 167 & 183 & 198 \\
19.5 mm & 40 & 76 & 101 & 131 & 153 & 165 \\
2\#1 unimorph & 26.5 mm & 94 & 130 & 164 & 196 & 217 & 238 \\
33.5 mm & 170 & 219 & 261 & 304 & 331 & 355 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Peak-to-peak voltages (V) from 1#1 and 2#1 PZT4 patches (_f_ = 1 Hz). Figure 9: Average powers from PZT4 patch of 1#1 on unimorph PCS of 1# piezoelectric brick versus the load resistance and the force arm length (_F_ = 500 N, \(f\) = 1 Hz). average powers from 2#2 and 2#4 PZT4 patches are measured by thinking of the influence of the foresaid factors. 2.1 Peak-to-Peak Voltages from PZT4 Patches of 2#1 on Unimorph PCS1 and 2#3 on Unimorph PCS2 (Open-Circuit)  
The peak-to-peak voltages from PZT4 patches of 2#1 on unimorph PCS1 and 2#3 on unimorph PCS2 are displayed in Figure 10a,b respectively. Specifically, for the force arm length of 19.5 mm, 26.5 mm and 33.5 mm, the peak-to-peak voltages from 2#1 PZT4 patch on unimorph PCS1 are (40 V, 76 V, 101 V, 131 V, 153 V, 165 V), (94 V, 130 V, 164 V, 196 V, 217 V, 238 V), and (170 V, 219 V, 261 V, 304 V, 331 V, 355 V), the peak-to-peak voltages from 2#3 PZT4 patch on unimorph PCS2 are (47 V, 81 V, 108 V, 135 V, 157 V, 173 V), (99 V, 137 V, 173 V, 200 V, 224 V, 244 V), and (179 V, 226 V, 269 V, 308 V, 339 V, 363 V) corresponding to amplitude of footstep excitation of 250 N, 300 N, 350 N, 400 N, 450 N and 500 N, respectively. The corresponding voltage densities from 2#3 PZT4 patch on unimorph PCS2 are computed as (0.019 V/mm\({}^{3}\), 0.032 V/mm\({}^{3}\), 0.043 V/mm\({}^{3}\), 0.054 V/mm\({}^{3}\), 0.063 V/mm\({}^{3}\), 0.069 V/mm\({}^{3}\)), (0.04 V/mm\({}^{3}\), 0.055 V/mm\({}^{3}\), 0.069 V/mm\({}^{3}\), 0.069 V/mm\({}^{3}\), 0.08 V/mm\({}^{3}\), 0.089 V/mm\({}^{3}\), 0.097 V/mm\({}^{3}\)) and (0.072 V/mm\({}^{3}\), 0.09 V/mm\({}^{3}\), 0.108 V/mm\({}^{3}\), 0.123 V/mm\({}^{3}\), 0.136 V/mm\({}^{3}\), 0.144 V/mm\({}^{3}\)) corresponding to amplitude of footstep excitation of 250 N, 300 N, 350 N, 400 N, 450 N and 500 N, respectively. It can be found that the peak-to-peak voltages from PZT4 patches of 2#1 on unimorph PCS1 and 2#3 on unimorph PCS2 all display an increasing trend with the increases in the amplitude of footstep excitation and the force arm length. This is because the increases in the two factors aforesaid leads to the increase in the surface strain and the output voltage of the PCSs. This phenomenon also can be theoretically explained by Equations (9)-(11), (14) and (15). To compare the energy harvesting ability of unimorph PCSs 1 and 2 of 2# piezoelectric brick, the peak-to-peak voltages from PZT4 patches of 2#1 on unimorph PCS1 and 2#3 on unimorph PCS2 were extracted and displayed in Figure 11a-c corresponding to the force arm length of 19.5 mm, 26.5 mm, and 33.5 mm, respectively. Obviously, in the same excitation and force arm, the output voltage from 2#3 PZT4 patch on unimorph PCS2 was slightly larger than the corresponding one from 2#1 PZT4 patch on unimorph PCS1. This is because there is a weakly internal energy dissipation in the energy transmission of exerted force from PCS2 to PCS1.