Topology-Driven Insights Into Rectifier Circuits for RFEH-Enabled Low-Power Wireless Sensors

Radio-frequency energy harvesting (RF-EH) and wireless power transfer (WPT) are emerging as enabling technologies for powering low-power, battery-constrained wireless platforms such as Internet of Things (IoT) nodes, RFID tags, biomedical implants, and biotelemetry systems. These applications demand reliable, maintenance-free power sources because battery replacement is often impractical, costly, or infeasible. Among the key circuit blocks in RF-EH/WPT systems, the rectifier is particularly critical, as it converts incident RF energy into usable DC power and directly governs the achievable power-conversion performance. Despite substantial progress, rectifier design remains challenging under practical operating conditions owing to ultra-low available input power, strong input-impedance variation with power level and load, and inherent trade-offs among sensitivity, efficiency, output voltage, number of stages, and complexity in multi-stage architectures. This paper presents a comprehensive, topology-driven review of rectifier circuits for sub-6-GHz RF-EH/WPT applications, covering series, shunt, voltage-doubler, and major voltage-multiplier/charge-pump topologies. Their operating mechanisms, performance characteristics, and design trade-offs are critically analyzed with respect to RF-to-DC power conversion efficiency (PCE), output voltage, load dependence, input power, and stage count. Special emphasis is placed on the influence of the number of stages, showing that rectifier performance is governed by an application-dependent optimum rather than by simply increasing the number of stages. The review also highlights emerging design strategies, including adaptive impedance matching, multiband rectification, and antenna-rectifier co-design, to improve robustness under realistic operating conditions. The resulting framework provides practical guidance for selecting and optimizing rectifier topologies in energy-autonomous, low-power wireless systems.