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oai:figshare.com:article/32826296 2026-10-01T16:09:08Z portal_1172 item_type_8 month_year_10_2026

RF energy harvesting for energy autonomous IoT devices Aaron Graham (5325191) PUREID: 684105917 Metamaterials RF energy harvesting superdirectivity RF-to-DC rectification circular polarisation metasurface The rapid expansion of the Internet of Things (IoT) creates an urgent need for sustainable power solutions. Conventional batteries are costly, short-lived, and environmentally unsustainable, motivating research into ambient radio frequency (RF) energy harvesting. Yet rectenna systems face persistent challenges: low incident power densities, sensitivity to polarisation and orientation, and limited directivity. <br><br>This thesis addresses these challenges through two complementary approaches: metamaterial-based rectennas and superdirective arrays. Metamaterial harvesters are developed that provide wideband, wide-angle, and polarisation-tolerant absorption in compact formats. These include tetra-band and circularly polarised designs that achieve milliwatt-level harvested power under low ambient excitations, demonstrating robust performance without the need for active circuitry. With harvesting levels of 1 mW of DC power at 5 μW/cm2 incident power density, and peak DC outputs of 18.75 mW at 60 μW/cm2. Also providing a view of scalable metamaterial based RF harvesting towards Watt harvesting.<br><br>In parallel, new superdirective rectenna arrays are presented that achieve realised gains exceeding 7 dBi from electrically small apertures. Using parasitic loading and phase-only optimisation, these arrays overcome the efficiency and complexity barriers traditionally associated with superdirectivity. A steerable five-element design further enables 360° beam coverage, maximising sensitivity to weak RF sources without bulky matching networks or amplifiers.<br><br>Finally, the work emphasises system-level co-design, integrating radiating structures with rectifying circuits to maintain efficiency at ultra-low input powers, below −20 dBm. Fabricated prototypes validate the concepts experimentally, achieving state-of-the-art performance for ambient RF harvesting. <br><br>Together, these contributions establish new methodologies for compact and practical rectennas. By combining metamaterial absorption with superdirective gain, the thesis demonstrates pathways toward scalable, battery-free IoT devices and autonomous wireless systems, with applications in smart cities, environmental monitoring, industrial automation, and biomedical technology. 2026-10-01T16:09:08Z Text Thesis 10.17034/32826296.v1 https://figshare.com/articles/thesis/RF_energy_harvesting_for_energy_autonomous_IoT_devices/32826296 All Rights Reserved