Modeling of RF energy scavenging for batteryless wireless sensors with low input power

RF energy scavenging enables batteryless operation of wireless sensors. In particular, a system with a central controller that transfers wireless energy to and exchanges information with RF energy scavenging sensors is very suitable for a wide range of applications. State-of-the-art analysis of RF energy scavenging is mostly based on RF-DC rectifier models operating with relatively high input power to achieve high rectification efficiency. However, to enable larger distance between the central controller and sensors and/or to increase the operating frequencies, which can lead to small and low-cost smart dust like sensors, a good model describing the RF-DC rectification with low input power is needed to aid system design and optimization. In this paper, we develop such a model. Using the model, we derive closed-form solutions for the equilibrium voltage and the input resistance of the rectifier. We further propose a quasi-static model to describe the dynamic charging of the capacitor in the rectifier. A comparison with circuit simulations using Cadence Virtuoso Spectre circuit simulator shows good match between our model and the circuit simulation.