An Ambient Energy Harvesting System for Passive RFID Applications

Radio-frequency identification(RFID)is the wireless use of electromagnetic fields to transfer data, for the purpose of automatically identifying and tracking tags attached to objects. It is one of hot topics recently. The power supply is one of key factors restricting the lifetime and performance of RFID. The main focus is to power RFID system with clear power source. In this work, a harvester consisting of a matching network, a rectifier and a load is investigated. The operation of a Schottky diode based rectifier which is the core part inthe harvester is researched seriously. The Schottky diode based rectifier consistingof single-stage or multi-stage of voltage doublers is applied in radio frequency (RF) power harvesting.Analytical modeling of the equivalent circuits composedof a resistor and a capacitor. The resistor and the capacitor from the analytical modeling are applied in the simulation of impedance matching. The design trade-off among the stages of the voltage doubler, load of the harvester, the output voltage and the efficiency is discussed owing to the variation of input impedance with the input power. Moreover, a trade-off betweenthe load inthe harvester and the stages of the voltage doubler is stated based on the analysis of the simulation resultsby Advanced Design System (ADS)with the criteria that the output voltage is higher than 1V.Some conclusions about the harvester are obtained by the simulation and analysis. The sensitivity of the harvester is around -23dBm. Rectifiers with more stages have lower input impedance and lower speeds of variation in input impedance. Larger loading impedance in the harvester leads to higher output voltage but lower conversion efficiency. Four-stage voltage doubler and 5M ohm load should be chosen when the input power ranges from -23 to -20dBm. Two-stage voltage doubler with 500k ohm load is a better choice with input power between -20 and -15dBm. For input power from -15 to -5dBm, single-stage voltage doubler and 50k ohm are utilized. When the input power is larger than -5dBm, two-stage voltage doubler and 50k ohm should be chosen