| Radio frequency (RF) wireless energy transfer and energy harvesting from external sources promise a battery-free paradigm for resource constrained wireless sensor networks (WSNs). The objective of this thesis is to advance the engineering of these energy harvesting components interfaced with off-the-shelf motes and formulate the design of higher layer link and routing protocols for a WSN composed of such motes. The specific contributions of the thesis include: (i) optimization and implementation of RF energy harvesting circuits, (ii) medium access control protocol for scenarios with multiple energy transmitters, (iii) cross-layer protocol design that includes joint duty cycle determination and routing, and (iv) the impact of mobile energy transmitters and the relative positions of the event locations.;Our hardware design allows the energy harvesting circuit to be more receptive in low input power region over existing commercial solutions. We propose an optimization approach for choosing circuit components that enables operation within ±20 dBm of incident RF signal power. A PCB fabrication of our circuit demonstrates that it can run a commercial Mica2 sensor mote in duty cycle at -6 dBm incident RF power and yield 100% improvement in efficiency over existing designs. In the second contribution, through an experimental study, we demonstrate how the placement, the chosen frequency, and number of the RF energy transmitters affect the sensor charging time. These studies are then used to design a MAC protocol called RF-MAC that optimizes energy delivery to sensor nodes on request, while minimizing disruption to data communication. Our approach reveals 112% average network throughput improvement over the classical unslotted CSMA MAC protocol. Our cross-layer protocol design provides a joint hardware-software optimization by allowing the selection of the energy storage capacitor, apart from the route and duty cycle determination. We adapt AODV for this design, using new route selection metrics and route management mechanisms. Finally, we investigated the impact of mobile transmitters with two different mobility models, and provided guidelines on which of them may be adopted based on the distribution of the events and actors.;In summary, this thesis considers a holistic view of energy harvesting WSNs, from device design to its eventual deployment. |
