## 9 Conclusions  
This paper has provided a comprehensive review of RFEH technologies, covering the fundamental principles, system architectures, recent technological developments, applications, challenges, and future opportunities. Key advancements have been recorded in rectenna design, impedance matching networks, metamaterial-assisted harvesting, and AI-driven energy optimization, resulting in improved RF-to-DC conversion efficiencies and more robust multi-band operation. The applications explored across smart cities, biomedical devices, industrial IoT, smart agriculture, and satellite communications highlight the growing significance of RFEH in enabling self-sustaining, maintenance-free electronic systems. However, the review also identified persistent challenges, including low ambient RF power density, unpredictable energy availability, antenna size limitations, electromagnetic interference, and regulatory constraints, that must be addressed to realize the full potential of this technology. The prospects for RFEH are highly promising, especially as the world moves toward the large-scale deployment of 5G, 6G, and future communication systems. Emerging technologies such as reconfigurable energy-harvesting systems, advanced materials for high-efficiency rectennas, AI-enhanced resource management frameworks, and hybrid energy-harvesting solutions are expected to drive further breakthroughs. To fully harness these opportunities, future research should focus on developing comprehensive implementation roadmaps that encompass pilot-scale deployment, standardization protocols, and cost-effective manufacturing processes. There is a critical need for multidisciplinary approaches combining material science, RF engineering, machine learning, and regulatory policy to design adaptive, environment-aware RF harvesting systems capable of operating efficiently under real-world conditions. The exploration of AI-driven predictive energy management and federated learning in distributed harvester networks can optimize energy capture and consumption dynamically. Additionally, hybrid harvesting architectures, integrating RF with solar, thermal, and vibrational energy sources, will improve reliability and broaden application scenarios. As research and development efforts continue to bridge existing performance gaps, RF energy harvesting is poised to become a cornerstone technology for self-powered IoT ecosystems, resilient smart infrastructures, and sustainable wireless communication networks. Further investigation into large-scale commercialization models, including energy-as-a-service platforms and modular plug-and-play harvesting units, will be vital to accelerate adoption across diverse markets. Moreover, the establishment of global regulatory frameworks, addressing spectrum usage, emission limits, and interoperability standards, is essential to remove current legal and operational uncertainties. By addressing current technical and regulatory barriers, RFEH can unlock a future where millions of devices operate autonomously, contributing to a more intelligent, connected, and energy-efficient world.  
S.N.A.: conceptualization, data curation, validation, writing--original draft. E.R.O.: investigation, formal analysis, writing--review & editing. S.H.E.: visualization, resources, writing--review & editing. A.O.N.: methodology, project administration, funding acquisition, supervision. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Data Availability Statement:** No new data were created or analyzed in this study.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Raysoft AssetAnalytics. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.