Cognitive RF energy harvesting: from design to applications.

• Online Access: http://hdl.handle.net/2047/D20323959

Radio frequency energy harvesting (RF-EH) allows powering low-power electronic devices without wires, and batteries, and promises self-sustainable and energy-neutral paradigms for Internet of Things (IoT) and wireless sensor network (WSN) applications. The objective of this dissertation is to advance the design of RF energy harvesting circuits interfaced with commercial-available IoT and wireless sensor motes, and design specialized circuit variants applicable for example selfpowered (battery-free) and wireless charging applications. The distinguishing contributions of the dissertation include: (i) spatio-temporal and multi-frequency study of RF signal strength distribution, (ii) design, optimization and application of re-configurable multiband RF energy harvesting circuit, (iii) distributed RF beamforming for wireless charging of IoT, (iv) design and implementation of capacitive touch energy harvesting system, (v)design of battery-less Bluetooth Low Energy Beacon (BLE) device. Our study of RF signal strength distribution conducted in Boston, USA, indicates locations and associated RF bands for practical outdoor deployment of RF-EH technology. Our design incorporates an adjustable circuit for harvesting from multiple spectrum bands, including LTE 700MHz, GSM 850MHz, and ISM 900-MHz bands using one single circuit. Our design is fabricated on printed circuit board with comprehensive evaluations at each associated frequency for the power conversion efficiency (PCE). In addition, we characterize the charging performance and demonstrate powering COTS sensors outdoors. Results reveal more than 45% PCE for our prototype design. We introduce a new architecture for next-generation wireless charging systems that acts as an integrated hardware and software solution. It consists of a software controller, programmable energy transmitters with distributed energy beamforming, and multi-band energy harvesting circuits. Our system realizes a software-defined wireless charging system through separation of controller, energy, and hardware planes. We demonstrate the working our indoor prototype with extensive experimental measurements leading to insights on how to design other closed loop-based wireless charging architectures and systems. We explore the feasibility of capacitive touch-screen as an energy source and show possibility of energy harvesting using the electric field created on the touch-screen surface by prototyping new circuit designs. Finally, we design a new BLE beacon device powered by an adjustable and miniature RF-EH circuit taking into account the power consumption profile of BLE beacon device, and energy harvesting range.