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PhD Oral Preliminary Examination – Kamala Raghavan Sadagopan


Wednesday, April 18, 2018 10:00 AM - 12:00 PM

WiFi-Backchannel Wireless Energy Harvester with Antenna-Rectifier-Boost Converter Co-design for Wireless Sensor Networks

Wireless sensor networks (WSN) for the Internet of Things require long lifetimes with small formfactors for easy deployment in myriads. The need for small formfactors precludes the use of large batteries. Further, battery replacement is undesirable considering the large numbers. Energy autonomy coupled with ultra-low power (ULP) circuits constitute a low cost, area-efficient solution for WSN. With WiFi device shipments expected to surpass 20 billion in 2018 (WiFi Alliance), the ubiquity of these device transmissions can be leveraged by wireless energy harvesters to power WSN applications. However, state-of-the-art wireless energy harvester sensitivities are in the -30dBm range whereas ULP wireless receiver sensitivities in are in the -45dBm to -60dBm range. Bridging this gap in sensitivity can enable longer ranges of operation for WSN, not limited by wireless energy harvesting. However, achieving excellent harvester sensitivities in area-constrained applications is a significant challenge due to small antenna sizes.

In this work, we present an ultra-low quiescent power WiFi-backchannel wireless-energy harvester with antenna-rectifier-boost-converter co-design for area-constrained applications. The antenna-rectifier output is boosted using a DC-DC converter to achieve a higher cold-start sensitivity. The converter's input impedance is optimized to extract maximum power from the antenna-rectifier and the converter switches are optimized to minimize losses at sensitivity for low quiescent power operation.

This harvester - fabricated in 65nm CMOS - achieves a high sensitivity of -33dBm in cold start and -36dBm in the primary mode with a continuous-wave source with a low quiescent power consumption of 960pW and occupies 1.97cm2 including the antenna. The harvester also demonstrates WiFi-backchannel charging from a commercially available WiFi 802.11b/g/n TX configured as an access point. The WiFi TX radiates 14dBm at 1% duty-cycle and is placed 1.25m away from the harvester. A harvesting range of up to 7.5m is achievable at an equivalent-isotropically-radiated-power (EIRP) of 30dBm (ISM limit for an isotropic antenna); therefore demonstrating ambient WiFi as a viable source of wireless power for WSN.

Major Advisor: Arun Natarajan
Committee: Matthew Johnston
Committee: Un-Ku Moon
Committee: Andreas Weisshaar
GCR: Yun-Shik Lee


Kelley Engineering Center (campus map)
3114
Calvin Hughes
1 541 737 3168
Calvin.Hughes at oregonstate.edu
Sch Elect Engr/Comp Sci
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