Wide-band, Quasi-isotropic, km-range RF Energy Harvesters for Perpetual IoT
Jung, Eui Min
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This research demonstrates, through real-world field-tests, an ambient RF (radio frequency) energy harvesting system, fabricated on low cost FR4 (flame retardant 4), capable of harvesting from all surrounding UHF-TV (ultra high frequency television) and FM (frequency modulation) towers across km ranges in all UHF-TV and FM frequencies simultaneously to perpetually power a WSN (wireless sensor node). The broader impact of this research is to encourage researchers in the field to focus their efforts on real-world usability, thereby advancing ambient RF energy harvesting towards widespread adoption. The system achieves -10 dB matching across the entire frequency bands. The FBW (fractional bandwidth) is as wide as 31 % for the UHF-TV portion and 23 % for the FM portion. For UHF-TV, front and rear antenna gains combined is 1 or greater across all θ and ϕ, allowing isotropic harvesting (omnidirectional for FM). The RF-dc efficiency is as high as 70 % (56 % for FM). The system is as sensitive as -18 dBm (-17 dBm for FM). The UHF-TV portion harvested as much as 231 μW across 5.83 km (885 μW across 1.53 km for FM). The alignment-free, channel-agnostic nature demonstrates potential for ambient RF energy harvesting's adaption by users outside of the RF community who are not expected to be familiar with antenna alignment and frequency selection.