## 7 Conclusions  
In view of the low output power density of the existing footstep harvesters, two pairs of distinctive LPCBs and the corresponding piezoelectric brick models are developed to improve the utilization efficiency of the piezoelectric patches used in the bricks. A theory model of the aforesaid LPCB is established to analyze its dynamic performance. Two pairs of LPCBs and two piezoelectric brick specimens are customized and a series of experiments are carried out. Some numerical computations based on the theory model of LPCB are conducted. According to the experiment and simulation results, some valuable conclusions can be drawn as follows:  
1. The force amplification factor increases with the increase of amplitude of footstep excitation and the energy harvesting ability of the piezoelectric brick can be improved by using the substrate material with a small young's modulus;
2. For any PZT4 patch bonded on LPCB in 1# or 2# piezoelectric brick, the output peak voltage in forced vibration period is far greater than that in the free vibration period, because the strain amplitude of the PZT4 patch in the forced vibration period is much bigger than that in free vibration period;
3. The average powers from PZT4 patches bonded on upper surfaces in PCSs are slightly larger than the corresponding ones from PZT4 patches bonded on lower surfaces in PCSs, which is because the strain energy in PCS transfers from stretching surface to pressing surface in the vibration process and there is a bigger energy dissipation in the transaction from upper surface to the lower surface compared to from lower surface to upper surface;
4. The output voltages and powers from PZT4 patches of 2# piezoelectric brick are notably larger than the corresponding ones from PZT4 patches of 1# piezoelectric brick in the same excitation; the main reason is the bending rigidity of 2# piezoelectric brick is less than that of 1# piezoelectric brick;
5. For 2# piezoelectric brick, the output voltages and powers from PZT4 patches on PCS2 are slightly larger than the corresponding ones from PZT4 patches on PCS1, because there is energy dissipation of exerted force in the transmission from PCS2 to PCS1;
6. The measured voltage (voltage density) and the output average power (power density) from 2# piezoelectric brick can reach up to 376 V (0.15 V/mm\({}^{3}\)) and 94.72 mW (37.89 \(\mu W/\)mm\({}^{3}\)) for a PZT4 patch with a dimension of 50 mm \(\times\) 50 mm \(\times\) 1 mm.  
Figure 21: RMS of voltages and average powers from 1#1 PZT4 patch of 1# piezoelectric brick with Babbitt metal substrate versus the force arm length of LPCB and the footstep excitation amplitude. (**a**) RMS of voltages; (**b**) Average powers.  
**Author Contributions:** [PERSON] and [PERSON] incepted the research. [PERSON] and [PERSON] designed the experiments. [PERSON] and [PERSON] conducted the experiments. [PERSON] and [PERSON] analyzed the data. [PERSON], [PERSON], [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was partially funded by Major Project for Special Technology Innovation of Hubei Province [2019 AAA011] and PetroChina Innovation foundation [2017 D-5007-0604].  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** All data details about this research have been displayed in the manuscript.  
**Conflicts of Interest:** The authors declare no conflict of interest.