Rectifier design for radio frequency energy harvesting system

Abstract

This thesis presents the development of rectifying circuits suitable for Radio Frequency (RF) energy harvesting application with dual-band capabilities. The main contribution of this thesis is the development of compact dual-band two-stage rectifier with high efficiency. Firstly, a voltage doubler rectifying circuit is designed to get a compact size. A source-pull simulation of matching circuit is used to find the optimal load impedance and enhance the conversion efficiency over the frequency range. The accuracy of the design has been justified by the simulation and measurement results. Secondly, a dual-band impedance matching network based on transmission line is developed. A short stub and general impedance transformer are designed to match different complex impedance at the two operating frequencies. Measurement results have fully demonstrated. Thirdly, a new rectifier circuit is proposed. It employs a dual-band multi resonant matching network and a high efficiency modified quadruplor rectifier for harvesting the ambient RF power at both 2.45 GHz Global System for Mobile Communications (GSM) and 5.8 GHz Wireless Local Area Network (WLAN). An attempt was made for matching network with a series of combination of a capacitor and inductor with a parallel LC tank. For rectifier circuit part, low power harvested from the RF is boosted up using two-stage of voltage multiplier and the input capacitor is rearranged to be in parallel connection to get smaller size and uniform pressure on diode. The prototypes are developed, and simulation results are obtained. The proposed rectifier is proven to exhibit greatly higher output voltage and efficiency compared to the conventional circuit. The rectifier is designed on the FR-4 board. Its capability of working within two frequency bands at 2.45 GHz and 5.8 GHz is verified by measurement. The proposed rectifier has met the requirement of high conversion efficiency (79.1% and 78.4% at the respective 2.45 GHz and 5.8 GHz), and able to boost up to the maximum voltage level of 14V at 20 dBm input power. Hence, the aims of this research have been achieved and are practically suitable for the use in wireless sensor networks and low power devices.