## 2 Design of the Energy Harvester
### Simulation  
Based on a simulation, this section describes the process of energy harvesting from piezoelectric devices to obtain the maximum power from piezoelectric modules. This simulation, which was performed using LTspice, included an integrated piezoelectric energy harvesting circuit board (LTC-3588-1). The parameters used to simulate the piezoelectric energy harvesting circuit were an input voltage of 24 V, a frequency of 41 Hz, an internal  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Test Scenarios and Configurations** & **Method** & **Reference** \\ \hline \multirow{6}{*}{Introduced piezoelectric energy harvesting from traffic-induced pavement vibrations} & Comparative analysis of various disclosed piezoelectric harvesting device technology and material configurations was examined using different cover plates. & \\ \cline{1-1}  & Evaluated their application & \\ \cline{1-1}  & Prepared stacked piezoelectric energy harvesting units for pavements and evaluated their performance & performance in terms of electrode structure (resistivity and cost) and technical characteristics (output power and durability) & [56] \\ \cline{1-1}  & Modeled and optimized an underfloor piezoelectric stacked energy harvester utilizing a force amplification frame & Optimized the device to suit a range of typical inputs, including walking, jogging, and multiple other pedestrian load conditions & [57] \\ \hline \multirow{2}{*}{Maximized the benefits from piezoelectric energy harvesting floor in buildings’ interior spaces, despite their being low pedestrian-traffic spaces} & Used various piezoelectric technology types and spreading to correlate between needed power and pedestrian density & [58] \\ \cline{1-1}  & Evaluated energy output and mechanical failure of piezoelectric energy harvester for roadway applications & Experimental testing and numerical modeling (finite element simulation) of energy harvester & [59] \\ \cline{1-1}  & Designed and assessed stacked piezoelectric energy harvesting power-generation devices for pavements & Mechanical testing and simulation (MTS) determined durability and power generation performance. & [60] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Laboratory and field studies of piezoelectric energy harvesting.  
resistance of 119 k\(\Omega\), an output voltage of 3.3 V, and an output current of 30 mA. In addition, the time step using for simulation software was 2 \(\times\) 10\({}^{-6}\) s. The electrical energy obtained via the excitation of the piezoelectric device, which was connected to a rectifier, was transmitted for conversion into a direct current (DC). It was passed through a capacitor to reduce output voltage ripples and subsequently through a synchronous buck converter circuit to realize a desirable, stable voltage level. Finally, the energy received by the battery charging circuit was stored in a lithium-ion battery to support the load demands. A schematic of the energy harvesting circuit using a piezoelectric device, as obtained from LTSpice, is presented in Figure 2.  
The simulation results indicate that an alternating current (AC) voltage was generated when the piezoelectric device was excited by mechanical forces such as vibrations or pressures. The characteristics of the waves varied according to the mechanical force. The resulting voltage was relatively constant, approximately 10-15 V. When the piezoelectric device was continuously subjected to mechanical energy, the input current remained stable at approximately 70-115 uA, while the output side produced a rectified and stabilized voltage of approximately 3.3 V from the synchronous buck converter signal. The output current was characterized as a pulse signal according to the mechanical force obtained under a maximum current of approximately 30 mA, as shown in Figure 3.  
Figure 3: _Cont._  
Figure 2: Schematic of energy harvesting circuit using piezoelectric device, obtained via LTSpice.