Metamaterial rectenna based RF energy harvesterTools Olule, Lillian Joyce Among (2019) Metamaterial rectenna based RF energy harvester. PhD thesis, University of Nottingham.
AbstractIncreasing energy demands have fuelled research into alternative, green energy harvesting methods such as Radio Frequency Energy Harvesting (RF EH). RF EH can be implemented using metamaterials; artificially engineered periodic structures with unique properties that are not found in nature. In most approaches, metamaterials are usually added to the antenna to improve the performance of the RF EH system. In this research, however, two metamaterials namely the Electromagnetic Bandgap (EBG) and Spiral Resonator (SR) have been used exclusively as novel RF collectors (metamaterial antennas) in place of the conventional microstrip patch antenna (MPA). Four novel metamaterial antennas are proposed and used to demonstrate RF EH. The first antenna operates at 5.8 GHz and uses the surface wave suppression ability of the EBG to achieve a 3 dB higher gain than a similarly resonant MPA. An empirical model is developed for predicting the antenna’s S-parameters and input impedance. The second antenna also utilizes EBG, has even higher gain, and has dual resonances at 5.36 GHz and 5.82 GHz. The third antenna operates at 2.45 GHz, and utilizes the miniaturization property of the SR to provide a 60 % size reduction as compared to an MPA. The final antenna utilizes arrays of both EBG and SR to achieve triple band resonance. It exhibits a higher gain and is a more compact solution as compared to the single band antennas employing a single metamaterial type. Single band, dual band and triple band rectifier circuits are fabricated and combined with the respective antennas to form RF EH devices. For low power environments (-20 dB to 0 dB), the single band devices give output voltages of over 0.2 V, and the multiband devices, due to the concurrent harvesting from the individual frequency bands, give higher output voltages of over 1.2 V. These solutions present improved RF EH designs for charging low power devices.
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