A comprehensive review of ambient RF energy harvesting in wireless systems

Radio Frequency Energy Harvesting (RFEH) has emerged as a promising solution to power the next generation of low-power devices in the Internet of Things (IoT), smart cities, healthcare, and industrial monitoring. By converting ambient or dedicated RF signals into usable electrical energy, RFEH enables battery-free, maintenance-free, and sustainable device operation. This review explores the fundamentals and system architecture of RFEH, including rectenna design, impedance matching, energy management, and hybrid harvesting strategies. Advancements in multi-band antennas, metamaterials, and rectifier topologies are analyzed alongside emerging concepts like ambient backscatter communication, AI-driven energy optimization, and wireless information and power transfer (WIPT). Furthermore, we discuss applications across biomedical systems, structural health monitoring, and wearable electronics, while addressing challenges such as low energy density, miniaturization, interference, and standardization. Finally, the review highlights future research directions, emphasizing the role of 5G/6G networks, edge intelligence, and hybrid systems in shaping resilient, self-sustaining wireless ecosystems.