Examination Committee

Prof Baoling HUANG, MAE/HKUST (Chairperson)
Prof Ross MURCH, ECE/HKUST (Thesis Supervisor)
Prof Yang HAO, School of Electronic Engineering and Computer Science, University of London (External Examiner)
Prof Chi Ying TSUI, ECE/HKUST
Prof Roger CHENG, ECE/HKUST
Prof Ilias DIMITRAKOPOULOS, CIVL/HKUST

Abstract

Ambient RF energy harvesting is a potential technique for alleviating the need for battery replacement or recharging in applications such as the Internet-of-Things (IoT). It is based on extracting energy from the environment by leveraging the RF signals radiated by communication infrastructure such as WiFi, cellular and broadcast systems. A key problem in ambient RF energy harvesting is that the extremely low RF power density of the ambient RF environment significantly limits the power available for harvesting and this results in low RF-to-DC power conversion efficiencies.

In this thesis the use of multiple antenna systems for enhanced ambient RF energy harvesting is investigated. Various impedance matching techniques are proposed to address the concern of mutual coupling in compact multiple antenna systems. Simulation results shows that the proposed impedance matching technique can harvest more RF power while maintaining good bandwidth. Designing the multiport antenna to achieve more harvested RF power in a compact configuration without impedance matching is then focused on. Two examples of rectenna design for ambient RF energy harvesting are presented. The first is a multiport pixel rectenna which is optimized to maximize the harvested power using a new algorithm called successive exhaustive Boolean optimization. The optimized multiport pixel antenna can harvest more energy in a compact configuration compared to other techniques such as impedance matching. The second design combines multiband rectenna with multiport rectenna in ambient RF energy harvesting. A compact dual-port and triple band L-probe patch rectenna is formed which fully utilizes the ambient energy, addressing the problem of low power density. It can be concluded that the use of multiple antennas for ambient RF energy harvesting can provide increased harvested energy and output voltage as compared to a similarly sized single antenna design. Furthermore it is also demonstrated that ambient RF energy harvesting can be a viable approach to powering IoT devices.