Demonstration of an Efficient Ambient Radio-Frequency and Microwave Energy Harvesting System with High Sensitivity and DC Output

The great potential to harvest and utilize ambient Radio-frequency and microwave power has led to much research as the occurrence of a worldwide coverage of radio waves during the past decade. However, RF harvesting circuits have already been proved for more than a half century, only a small number of them have been able to be activated freely without dedicated sources and harvest available ambient RF energy that typically has a power density ranging from 0.001 to 0.1 µW/cm2.
This thesis presents a detail description of each element of an RF energy harvesting system operating at 2.45 GHz, including an antenna, an RF-to-DC conversion rectifier and an integrated module of DC-DC up-conversion and power management. This thesis does not focus on the design of the antenna and the integrated module, both of which are products designed by Texas Instruments.
The key section of this thesis is concerned about the RF-to-DC rectifier, which is the core part that converts collected RF power to applicable DC power. In this section, the reasons that only a small number of rectifiers can work efficiently with ambient RF power levels are presented based on nonlinear model analyses of a diode, the dominant rectifying device in RF and microwave power harvesters. And the mechanism of overall power conversion efficiency (PCE) of the rectifier is explained in this analysis. Besides, a prototype of a modified rectifier is designed, fabricated and measured to demonstrate the potential ability to work in ambient power regions.
The entire RF energy harvesting system is tested with an RF signal generator at the end of this thesis. The overall efficiency of the harvester can reach 5.17% to deliver a DC output voltage of 1.8 V with an incident power of -10 dBm. And it can have an estimated efficiency of 13% to output a high DC voltage of 4.2V when charging a rechargeable battery MS920SE with the same power. At last, a comparison among power harvesters is given, showing a performance of high sensitivity and DC voltage output of this work in the mode of battery charging. Potential solutions to some unsolved issues in this thesis have been discussed and can be further studied in future works.