Graduate Thesis Or Dissertation
 

A Wireless Energy Harvester for Powering Event-driven Internet-of-things Applications and Battery Charging

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7p88cp598

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  • The need for sustainably powering unobtrusive internet-of-things applications has led to an interest in energy harvesting. Particularly, the proliferation of wireless communication and devices in the 2.4 GHz Industrial Scientificc Medical (ISM) band creates an opportunity to leverage commonly used devices for RF powering. This dissertation presents a low-quiescent-power energy harvester architecture and techniques for enhancing wireless powering range and demonstrates long-range RF-powered sensor operation and chip-scale battery charging in 65nm CMOS. First, the challenges in long-range RF-powering at 2.4 GHz are presented in the context of the Federal Communications Commission (FCC) regulations. Techniques and rectifier architectures employed to improve harvester sensitivity are then discussed followed by trade-offs of long-range powering on system design. The design of a cm-scale RF-energy harvester for RF powering in the 2.4 GHz ISM band is described. The harvester includes a loop antenna, rectifier and boost converter. The antenna and rectifier are codesigned to maximize passive gain for a small constrained antenna area. The boost converter is designed while considering cold-start operation and nanowatt-scale available power from the rectifier for RF incident power <-33 dBm. Low-power design in the power management unit and converter leads to 960pW quiescent power. The harvester implementation in 65-nm CMOS occupies 1.6 sq. mm while the antenna occupies 1.27 sq. cm. The proposed design optimization approach leads to a sensitivity of -33dBm in cold start and -36dBm in the primary mode for 1V output. Measurements using a commercial WiFi TX demonstrate ranges of up to 1.25m for 14dBm output power with 1.3% TX duty-cycling in WiFi access-point mode, demonstrating the feasibility of powering sensors from RF power beacons in the 2.4 GHz ISM band as well as from background WiFi transmissions. A 2.4GHz pH-sensor radio for wireless biomedical and environmental sensing demonstrating the feasibility of long-range RF-powered sensors is presented. A 960 pW-quiescent-power harvester combined with a MIMO RF-powering approach is used to further enhance RF powering range by 40% without handshaking between MIMO TX and sensor node. The harvester achieves -36dBm cold-start sensitivity with respect to each MIMO TX element corresponding to 4m range with 16dBm TX. The 65nm CMOS harvester powers a 400nW wake-up RX, 1.45mW Class-D TX and 30 microwatt sensor interface, and the complete SoC occupies 1.9 sq. mm. An end-to-end 2.4 GHz, RF-powered FCC-compatible battery-charger IC for long-range miniature chip-scale battery charging is presented to achieve sustainable powering for IoT sensors. A bulk-connected rectier is used to improve efficiency by reducing leakage and an integrated rectifier resonant-frequency tuning loop is employed to maximize passive gain by tracking input RF frequency for frequency-hopped source. A boost converter placed in cascade with the rectifier harvests efficiently across -27dBm to -17dBm RF available power and cold-starts without drawing any power from the battery, achieving state-of-the-art net positive charging for -21.5dBm incident power and 4.18% duty-cycled FCC-compliant frequency-hopped RF input assuming a steady-state 100 nA load.
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  • Pending Publication
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  • 2020-09-21 to 2022-10-22

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file details SadagopanKamalaRaghavan2020.pdf 2020-09-21 Público Baixar