## 1 Introduction
In order to understand the full potential of the RF energy harvesting process, in light of the latest developments, it can be useful to consider the evolution of the technology and applications that lies behind the concept. The two key elements in RF energy harvesting systems are the antenna and rectifying circuit, also known as the rectifying antenna. The performance efficiency of each RF energy harvesting system depends on the antenna efficiency and rectifying circuit efficiency. With advancements in technology, researchers and engineers have focused on improving the efficiency of RF energy harvesting systems, miniaturization and the integration of RF energy-harvesting components. This has led to the development of compact and lightweight RF harvesting modules that can be integrated into various devices and systems, including wearables, IoT devices and Wireless Sensor Networks [10]. In light of technology advancements, traditional RF energy harvesting has focused on specific frequency bands. However, recent advancements have enabled the harvesting of energy from multiple frequency bands or even wideband signals [32]. This allows for the better utilization of available RF sources and increases the potential for energy harvesting in various environments. All of these chronological advancements have led to a diversity of applications of RF energy harvesting in various fields, such as Wireless Sensor Networks for environmental monitoring, industrial automation, smart cities, wearable devices, remote monitoring systems and low-power IoT devices, among others [33]. The development of battery-free or maintenance-free IoT devices will contribute to the faster development of the IoT, contributing to several aspects that drive economic growth and innovation [34]. For example, by enabling real-time monitoring, predictive maintenance, and automation, IoT devices will help businesses streamline their operations, reduce costs, enhance productivity [35], improve supply chain management, enhance customer experiences and identify new revenue opportunities [36; 37]. Data-driven decision making facilitated by IoT devices enables businesses to stay competitive in today's fast-paced economy. These devices enable automation, optimization and intelligent decision making, leading to increased efficiency, reduced waste, improved safety and enhanced customer experiences. By optimizing resource utilization, reducing energy consumption and enabling the efficient monitoring and management of assets, IoT devices promote sustainable business practices. This not only reduces costs but also addresses environmental challenges, making businesses more resilient in the face of economic and environmental uncertainties [38; 39; 40]. Along with the development of IoT devices, RF energy harvesting has tremendous implications for WSNs. The development of WSNs itself is closely related to one of the IoT devices presented above. Improved sensing capabilities have expanded the range of applications for WSNs across industries such as agriculture, healthcare, environmental monitoring and smart cities [41; 42; 43]. Most recently, WSNs have started to leverage artificial intelligence (AI) and machine learning (ML) techniques [44; 45; 46; 47]. AI and ML algorithms can analyze sensor data, identify patterns and make intelligent decisions. This integration enables WSNs to adapt dynamically to changing environments, optimize resource allocation and improve system performance. In conclusion, RF energy harvesting holds significant potential for the future development of the IoT and WSNs, providing a sustainable and reliable power source for these devices that can significantly extend their lifetime. Moreover, RF energy harvesting allows for more flexible and scalable deployments, even in remote or hard-to-reach locations, facilitating the expansion of IoT devices and sensors.