RF Energy Harvesting Integrated Circuits for Low-Power Sensors: A Review

Abstract

With the rapid proliferation of the Internet of Things (IoT), billions of distributed sensors have been deployed worldwide, creating overwhelming challenges associated with battery replacement and perpetual maintenance. To address these critical energy bottlenecks, radio frequency energy harvesting (RFEH) has emerged as a transformative solution for enabling battery-less, self-sustaining sensor nodes. In this article, we review the design challenges and recent advances in RFEH front ends tailored for such low-power sensing systems. Specifically, the fundamental limitations imposed by extremely low ambient radio frequency (RF) energy density and nonlinear rectifier impedance are analyzed. To establish the circuit-level foundation of RFEH operation, the cross-coupled differential-drive (CCDD) rectifier is adopted as a representative topology to analyze low-power conduction, cycle-by-cycle charge balance, and reverse leakage mechanisms. Various threshold-voltage compensation strategies, leakage suppression techniques, and tunable matching networks are surveyed to highlight tradeoffs among sensitivity, efficiency, and area. Building on this rectifier-level foundation, the discussion is extended to system-level RFEH design, including multiband energy aggregation, wide-input-range operation, interactions with power-management units (PMUs), energy storage and regulation, and load-aware energy delivery for stable long-term sensor operation. Finally, future research directions and a prospective architecture for enhanced RFEH efficiency are presented.