## 4 Results
#### 4.3.1 Rectifier Systems and Their RF Energy Harvesting Efficiency
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref.** & \begin{tabular}{c} **Output Power or** \\ **Voltage** \\ \end{tabular} & \begin{tabular}{c} **Gain in** \\ **(dBm)** \\ \end{tabular} & \
\begin{tabular}{c} **Efficiency** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Matching Network** \\ \end{tabular} \\ \hline
[66] & 0.3 V & — & — & Seven-stage Villard voltage multiplier circuit \\ \hline
[30] & 2.63 V & \(-5.8\) & 22 & — \\ \hline
[35] & 1.5 V & \(-15\) & 50 & Standard RFID chips and diplexer \\ \hline
[37] & 200 mV, 2 mW & 3 & 40 & Input open stub matching \\ \hline
[45] & 3 V, 14.4 mW & 11.6 & — & — \\ \hline
[53] & 1.92 V, 0.2 W & \(-15\) & 92.2 & Impedance-matching network \\ \hline
[57] & 2, 2.5 V & \(-15\) & 80, 91 & Impedance-matching circuit \\ \hline
[70] & 3.6 V & 4 & 70 & Four-port hybrid integrated with a differential rectifier \\ \hline
[72] & 0.5, 0.9, 1.1 V & 0 to 10 & 45, 42, 40 & Dual radial stub and transmission line \\ \hline
[73] & 2 V & \(-8\) & 61.7 & L-type matching and LPF \\ \hline
[83] & 1.42 V, 1.1 mW & \(-3\) and 0 & 38 & Parallel stub coupling and transmission line \\ \hline
[91] & 3.7 V & 5 & — & — \\ \hline
[96] & 0.8, 1.6 V & 0 & 2.6 & — \\ \hline
[99] & 63.7 mV & \(-5\) & 45 & — \\ \hline
[101] & 3.09 V & — & 66 & Impedance regulating stub \\ \hline
[102] & 1186 mV & 39 & — & — \\ \hline
[104] & 1.64 mW & 0 & 70 & Stub and dual matching \\ \hline
[105] & 2.17 V, 0.48 mW & \(-8.5\) & 52 & L-section matching network \\ \hline
[108] & 0.35, 0.17, 0.155, 0.085 V & \(-6.9\) & 96 & Coupled impedance network \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Constructive characteristics of rectifiers within the single-step classification. These include coupling network, efficiency, and power or voltage generated by the rectifier. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref.** & \begin{tabular}{c} **Output Power or** \\ **Voltage** \\ \end{tabular} & \begin{tabular}{c} **Gain in** \\ **(dBm)** \\ \end{tabular} & \
\begin{tabular}{c} **Efficiency** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Matching Network** \\ \end{tabular} \\ \hline
[29] & 1.8 V & \(<-20\) & 50 & — \\ \hline
[40] & — & — & — & — \\ \hline
[41] & \(\approx\)2 V & 0 to 23 & 75 & — \\ \hline
[46] & 1.811 V & 2 & 62 & Series inductor and shunt capacitor \\ \hline
[50] & \(3.98\cdot 10^{-7}\) mW & \(-19\) & 97.5 & Stubs. \\ \hline
[77] & 191 mV & \(-20\) & 48 & L-network with short and open stubs \\ \hline
[79] & 1 V & 20 & 40, 80 & Integrated inductive coil \\ \hline
[98] & — & 3 and 14 & 64, 55 & Direct matching network \\ \hline \hline \end{tabular}
\end{table} 
Table 18: Constructive characteristics of rectifiers within the multi-step classification. These include the coupling network, efficiency, and power or voltage generated by the rectifier. \begin{tabular}{c c c c c} \hline \hline
**Ref.** & \
\begin{tabular}{c} **Output Power** \\ **Voltage** \\ \end{tabular} & **Gain in (dBm)** &
\begin{tabular}{c} **Efficiency** \\ **(\%)** \\ \end{tabular} & **Matching Network** \\ \hline
[56] & — & 20 & 81.2 & Split-ring resonators (SRR) and metallic strips \\ \hline
[62] & 900 mV, 150 uW & \(-\)20 & 68 & Matching networks \\ \hline
[64] & 172 mV, 65 uW & 27.5 & 58 & — \\ \hline
[65] & 17.5 mV & \(-\)20 to \(-\)10 & 91 &
\begin{tabular}{c} T-stub in metamaterial, exponential wave \\ coplanar transmission line \\ \end{tabular} \\ \hline
[71] & 1.43 V & \(-\)2.5 and \(-\)1 & 64 & Double-stub matching network \\ \hline
[86] & 1.8 V & 21 & 63.5 & — \\ \hline \hline \end{tabular}   
* Half-wave  
Finally, half-wave rectifiers, while less efficient than full-wave designs, provide a simpler and more cost-effective solution for basic energy harvesting needs. Their minimal component requirements and ease of implementation make them suitable for low-power systems where simplicity and affordability take precedence over peak performance, as shown in Table 21.  
* Microwave  
Conversely, microwave rectifiers are precisely engineered for high-frequency operation.