## 2 Related Work
In their review, they analyzed difficulties in designing efficient antennas for low-power environments. Subsequently, they reviewed rectifier circuits and impedance-matching networks, underscoring how losses in these modules affect total efficiency. Finally, they proposed a general design framework for ambient RFEH systems, identifying key considerations for optimizing each stage (antenna/matching network/rectifier/power management). This work provides engineering lessons: for example, it highlights that to maximize captured energy, exact conjugate impedance matching between the antenna and rectifier must be achieved at the nanowatt-microwatt power level, and that Schottky diode design is critical for weak signal reception. Although the review is systematic in identifying design \"issues\" and even includes a table of recommendations, once again there is no consolidated quantitative analysis. [PERSON] et al. [24]--published late 2020 but commonly cited as 2021--conducted a systematic and taxonomic review of the energy harvesting field in WSNs. They considered 137 articles (1998-2020) selected from databases (Web of Science, Scopus) using explicit criteria: peer-reviewed publications, relevance, and high impact. Unlike previous, more narrative works, this study applied some bibliometric analysis and classified energy harvesting solutions along multiple axes. In particular, they proposed a taxonomic classification of EH systems in WSNs, segmenting them by source type, transducer type used, and storage methods. This taxonomy allowed them to highlight recent trends in self-powered WSNs, such as an increase in hybrid proposals combining various sources, and to identify underexplored areas. The results, presented in a structured manner, aid in understanding the distribution of efforts in the field up to 2020. However, despite its more systematic methodology, the nature of the collected data remains qualitative/descriptive. The authors neither experimentally evaluated any technique nor provided performance metric comparisons between studies. Furthermore, their focus was on classifying knowledge rather than drawing conclusions about absolute efficiency; therefore, it did not address in detail the performance of specific antenna and rectifier designs. [PERSON] et al. [5] offered a specialized review of antenna designs for RF rectennas, covering both ambient energy harvesting and directed wireless power transfer (WPT). This review acknowledges that the rectenna (antenna \(+\) rectifier) is a key element in any RFEH/WPT system, as it determines how much incident RF energy is ultimately converted into usable direct current (DC) power. The authors compiled numerous rectenna designs reported in the literature and categorized them according to two main criteria: (1) the impedance bandwidth between antenna and rectifier, and (2) the antenna's radiation properties. For each category, they identified an appropriate figure of merit and compared different prominent designs along that dimension. They provided comparative tables with characteristics of relevant designs, helping readers understand design trade-offs. An important finding was that no single optimal design exists; the optimal choice depends on whether the application is ambient harvesting or dedicated WPT. Regarding limitations, this review deliberately focuses on the antenna portion: advanced rectifier circuit aspects or energy management architectures are outside its scope. Likewise, although they compare reported parameters, they do not unify test conditions, thus precluding a cross-sectional statistical meta-analysis. [PERSON] et al. [25] published a review focused on multi-source energy harvesting techniques incorporated into antennas. Unlike other reviews centered solely on RF, this work encompassed multiple energy harvesting modalities (RF, solar photovoltaic, thermoelectric, piezoelectric) and their integration with antenna systems.