Integrated multiband front-end radio frequency energy harvesting system for low-power IOT devices / Lian Wen Xun

Lian , Wen Xun (2023) Integrated multiband front-end radio frequency energy harvesting system for low-power IOT devices / Lian Wen Xun. PhD thesis, Universiti Malaya.

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Abstract

The rapid growth of the Internet of Things (IoT) has driven the expansion of wireless sensor networks (WSNs). However, traditional battery-based power sources for WSNs are impractical due to their physical size and life-cycle limitations. As a result, energy harvesting has emerged as a viable renewable solution by converting ambient energy into usable electrical energy. Among all the energy harvesting sources, such as solar, thermal, kinetic, and Radio Frequency (RF), RF stands out as a suitable choice for WSNs due to its availability, especially when there is data communication; then, there will be RF energy. RF energy harvesting (RFEH) systems, consisting of crucial blocks such as the impedance matching network (IMN) and rectifier, plays a vital role in energy conversion. While most existing RFEH designs are off-chip, on-chip implementations are preferable for biomedical implants and IoT applications. Furthermore, relying solely on a single-band RFEH system limits the practicality when RF energy fluctuates, or the RF at the desired frequency is unavailable. Therefore, the development of multiband RFEH systems becomes crucial to address these challenges. In CMOS rectifier design, achieving high sensitivity for initiating the scavenging process is essential. Current rectifier topologies involve trade-offs such as the number of stages, transistor types, harvesting frequency, and enhancement techniques. The sensitivity of CMOS rectifiers to scavenge RF energy from longer distances requires further improvement. Moreover, extending the power dynamic range (PDR) of CMOS rectifiers presents challenges in performance trade-offs. To address these research gaps, this work aims to develop a novel mathematical design formulation for on-chip multiband IMN, along with a high- sensitivity cross-coupled differential drive (CCDD) rectifier and a wide PDR reconfigurable CMOS rectifier. The proposed mathematical model addresses the gaps in IMN design formulation for multiband RFEH systems. The designed tri-band RFEH system achieves peak power conversion efficiency (PCE) of 42.8%, 37.1%, and 30.4% at 900MHz, 1.9GHz, and 2.4GHz, respectively. The fabricated CCDD rectifier demonstrates a sensitivity of -22dBm and peak PCE of 86% at 900MHz. Furthermore, the novel reconfigurable rectifier achieves a PDR of 23dB with a peak PCE of 88.7%.

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