## 4 Results
#### 4.3.1 Rectifier Systems and Their RF Energy Harvesting Efficiency  
Figure 18 showcases various rectifier types, each possessing unique strengths and inherent trade-offs. Optimizing energy harvesting performance hinges on selecting the rectifier that best aligns with an application's specific operational requirements. Figure 18: Types of rectifier designs: (**a**) schematic half-wave rectifier, (**b**) half-wave rectifier, (**c**) ground half-wave rectifier; (**d**) schematic microwave rectifier, (**e**) microwave rectifier, (**f**) ground microwave rectifier; (**g**) schematic Schottky rectifier, (**h**) Schottky rectifier, (**i**) ground Schottky rectifier; (**j**) schematic single-step rectifier, (**k**) single-step rectifier, (**l**) ground single-step rectifier; (**m**) schematic full-wave rectifier, (**n**) full-wave rectifier, (**o**) ground full-wave rectifier; (**p**) schematic multi-step rectifier, (**q**) multi-step rectifier, and (**r**) ground multi-step rectifier. Each design has unique characteristics related to energy harvesting applications. These are representative figures of rectifiers, intended as a visual reference for design type but not necessarily functional with current dimensions. Analysis of the literature under review reveals the percentage distribution for each type of rectifier studied, as presented in Figure 19. Additionally, Table 16 offers a detailed classification of the articles included in this schematic review, providing further insight into the emphasis placed on different rectifier designs within energy harvesting applications. The results highlight that Schottky rectifiers dominate the research landscape, with a considerably higher presence in the literature compared to other rectifier types. Rectifier design significantly impacts the performance of energy harvesting systems, with each type offering distinct advantages tailored to specific applications. * Schottky  
Schottky rectifiers, characterized by their fast switching speeds and low forward voltage drop, are a cornerstone of high-efficiency energy conversion. These rectifiers excel in scenarios where minimizing power loss is crucial, such as in low-power wireless devices. Their performance is particularly advantageous in applications operating at high frequencies, where traditional diodes often fall short, as summarized in Table 17.  
* Multi-step  
Multi-step rectifiers are renowned for converting high-frequency signals into usable DC power with exceptional efficiency. Their cascaded architecture allows for enhanced voltage conversion, making them particularly suitable for applications requiring high output voltage at moderate power levels. This design is ideal for systems where maintaining high efficiency across a range of operating conditions is paramount, as shown in Table 18. \begin{table}
\begin{tabular}{c c} \hline
**Rectifiers** & **References** \\ \hline Schottky & [31; 32; 33; 34; 36; 39; 31; 33; 34; 47; 48; 51; 52; 55; 58; 60; 61; 63; 67; 75; 76; 78; 81; 82; 87; 91; 95; 100; 103; 107] \\ \hline Multi-step & [30; 35; 37; 45; 53; 57; 66; 70; 72; 73; 83; 91; 96; 99; 101; 104; 105; 108] \\ \hline Without & [38; 42; 49; 54; 59; 68; 74; 85; 88; 89; 90; 97] \\ \hline Single-step & [29; 40; 41; 46; 50; 77; 79; 98] \\ \hline Full-wave & [56; 62; 64; 65; 71; 86] \\ \hline Half-wave & [69; 84; 106] \\ \hline Microwave & [80] \\ \hline \end{tabular}  
* Multi-step rectifiers are renowned for converting high-frequency signals into usable DC power with exceptional efficiency. Their cascaded architecture allows for enhanced voltage conversion, making them particularly suitable for applications requiring high output voltage at moderate power levels. This design is ideal for systems where maintaining high efficiency across a range of operating conditions is paramount, as shown in Table 18.  
\end{table} 
Table 16: Article classification by rectifier. Figure 19: Percentage distribution of reviewed bibliography according to the type of rectifier analyzed.