## 3 Simulated and Measured Results
By connecting the receiving antenna to the matching network on the measured PCB, the multimeter measures the output voltage of approximately 1.702 V by setting a distance of 2.45 m between the Powercast transmitter and PCB, with an input power of 0.0 dBm. Figure 20 shows the measured setup of the proposed RF-energy-harvesting IC. Figure 17: Matching network used to obtain an input impedance of approximately 50 \(\Omega\). Figure 18: Measured results in the Z-smith chart at an input power of 0 dBm and RF of 915.0000 MHz. Table 3 summarizes the results for the designed RF-DC rectifier with the over-voltage protection circuit. Because the distance between the Powercast transmitter and test PCB was provided, the input power \(P_{in}\) (dBm), input return loss \(S_{1I}\) (dB), and DC output voltage \(\mathrm{V_{dc}}\) (V) were measured after the input impedance \(Z_{in}\) (\(\Omega\)) and its corresponding matching circuits [L (nH) and C (pF)] were completed. The results showed that the DC output voltage \(\mathrm{V_{dc}}\) varied from 0.291 V to 1.725 V with respect to the distance from 5.45 m to 0.55 m. The measured output voltages were lower than the simulated  
Figure 19: Measurement platform of the designed RF-energy-harvesting IC with capacitor. Figure 20: Measured setup of the proposed RF-energy-harvesting IC. results. A stable charging voltage \(\mathrm{V_{dd}}\) can be obtained through the LDO regulator. Figure 21 shows the measured DC output voltage \(\mathrm{V_{dc}}\) of the designed RF-DC rectifier with the over-voltage protection circuit with respect to the input power \(P_{in}\) from \(-20\) dBm to \(+10\) dBm. Please note that the measured DC output voltages were limited from \(1.682\) V to \(1.725\) V with respect to the input power from \(-2\) dBm to \(+10\) dBm in Figure 21.  
Finally, the simulated rectifier \(PCE\) was \(43.601\%\) at an input power \(P_{in}\) of \(-7\) dBm, and the simulated system \(PCE\) was \(29.873\%\) at an input power \(P_{in}\) and a load resistor of \(-12\) dBm and \(1\) M\(\Omega\)  
Figure 21: Measured DC output voltages of the RF-DC rectifier with over-voltage protection with respect to the input power. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Distance (m)**} & \multirow{2}{*}{\(Z_{in}\) (\(\Omega\))} & \multicolumn{3}{c}{**Matching Circuits**} & \multirow{2}{*}{\(P_{in}\) (dBm)} & \multirow{2}{*}{\(S_{II}\) (dB)} & \multirow{2}{*}{\(V_{dc}\) (V)} \\ \cline{3-3} \cline{5-7}  & & **Parallel (L)** & & & & \\ \hline  
respectively. The limitation of system integration is the reduction of the _PCE_ from 43.601% to 29.873%. The improvement of the system _PCE_ is a crucial concern. This study focused on increasing the system _PCE_ by changing the load resistor from 20 k\(\Omega\) to 38 k\(\Omega\). Figure 22 exhibits the measured system _PCE_ with respect to the input power \(P_{in}\) (dBm) and load resistor. The larger the load resistor is, the smaller the input power is. A large load resistor reduces load current, whereas it increases charging current \(\mathrm{I_{bat}}\) for the abrupt charging of the battery. This phenomenon provides the maximum system _PCE_ at a low input power. A trade-off was observed between the load resistor and the maximum system _PCE_. Moreover, the results indicate that the largest system _PCE_ of 40.556% was observed at a load resistor of 30 k\(\Omega\) and an input power \(P_{in}\) of \(-\)6 dBm. Table 4 shows the measured electrical characterizations of the proposed RF-energy-harvesting IC, which includes the power consumption, power delivery, and other electrical characterization facts. Table 5 summarizes the performance and compares the performance with that of other RF-DC rectifiers and RF-energy-harvesting ICs. The maximum rectifier _PCE_ obtained in this study was superior to that in [30], and the maximum _PCE_ of the RF-energy-harvesting IC was superior to that in [31].