## 6 Applications of RF Energy Harvesting
### Smart Cities  
In smart city infrastructure, RF energy harvesting plays a critical role in achieving sustainable urban development. By embedding RF energy harvesters into streetlights, security cameras, and IoT sensors, cities can establish large-scale wireless networks without relying on extensive cabling or frequent battery replacements. A recent study demonstrated the deployment of RF-powered streetlights capable of continuous operation by harvesting ambient energy from nearby 5G base stations, significantly reducing maintenance costs and enhancing environmental sustainability [87]. For instance, Seoul, South Korea, has initiated the installation of multifunctional smart poles that integrate street lighting, Wi-Fi access points, and CCTV cameras. These poles are designed to support various smart city applications, including environmental monitoring and public safety enhancements. While the primary power source is the electrical grid, the integration of energy-efficient technologies and the potential for incorporating energy-harvesting methods are being explored to further reduce energy consumption and maintenance costs [88]. Security cameras and environmental sensors equipped with RFEH capabilities can operate autonomously, improving urban surveillance and environmental monitoring while minimizing human  
Figure 10: RFEH applications [86].  
intervention. This approach lowers operational expenses and supports the deployment of the vast sensor networks necessary for real-time data collection within smart city infrastructures. EnOcean GmbH has developed battery-less wireless sensors that harvest energy from their environment, such as motion, light, and temperature differences. These sensors have been implemented in various smart building projects across Europe, enabling maintenance-free operation and reducing electronic waste. Their applications include occupancy detection, temperature monitoring, and energy management, contributing to the efficiency of smart city infrastructures [89]. Notably, security surveillance systems powered by RF harvesters have achieved uninterrupted functionality, even during grid failures, thereby strengthening public safety initiatives [90]. In Milan, Italy, research initiatives have focused on deploying autonomous RF-powered security cameras in metro stations. These systems are designed to operate without external power sources, maintaining real-time video feeds under varying electromagnetic conditions. This implementation aims to enhance public safety while reducing infrastructure costs associated with power supply and maintenance [91]. Furthermore, recent developments have introduced self-powered environmental sensors designed to monitor air quality, traffic flow, and energy consumption. These sensors, enabled by RF energy-harvesting technologies, form the foundation of data-driven decision-making in modern smart cities, allowing for optimized urban management and sustainable growth [92; 93]. Singapore's Cooperative and Unified Smart Traffic System (CRUISE) exemplifies the integration of AI with real-time data from sensors to optimize traffic flow and enhance pedestrian safety. While CRUISE primarily relies on data from various sensors, the potential incorporation of energy-harvesting technologies could further improve the sustainability and maintenance efficiency of such smart traffic systems [94].