Energy harvesting embedded wireless sensor system for building environment applications

For many wireless sensor networks applications, indoor light energy is the only ambient energy source commonly available. Many advantages and constraints co-exist in this technology. However, relatively few indoor light powered harvesters have been presented and much research remains to be carried out on a variety of related design considerations and trade-offs. This work presents a solution using the Tyndall mote and an indoor light powered wireless sensor node. It analyses design considerations on several issues such as indoor light characteristics, solar panel component choice, maximum power point tracking, energy storage elements and the trade-offs and choices between them.

Hybrid energy storage for energy harvesting powered wireless sensor networks

Science Foundation Ireland (CSET - Centre for Science, Engineering and Technology, grant 07/CE/I1147); Scientific Foundation Ireland (ITOBO (398-CRP))

Energy harvesting system design and optimization for wireless sensor networks

Wireless sensor networks (WSN) are becoming widely adopted for many applications including complicated tasks like building energy management. However, one major concern for WSN technologies is the short lifetime and high maintenance cost due to the limited battery energy. One of the solutions is to scavenge ambient energy, which is then rectified to power the WSN. The objective of this thesis was to investigate the feasibility of an ultra-low energy consumption power management system suitable for harvesting sub-mW photovoltaic and thermoelectric energy to power WSNs. To achieve this goal, energy harvesting system architectures have been analyzed. Detailed analysis of energy storage units (ESU) have led to an innovative ESU solution for the target applications. Battery-less, long-lifetime ESU and its associated power management circuitry, including fast-charge circuit, self-start circuit, output voltage regulation circuit and hybrid ESU, using a combination of super-capacitor and thin film battery, were developed to achieve continuous operation of energy harvester. Low start-up voltage DC/DC converters have been developed for 1mW level thermoelectric energy harvesting. The novel method of altering thermoelectric generator (TEG) configuration in order to match impedance has been verified in this work. Novel maximum power point tracking (MPPT) circuits, exploring the fractional open circuit voltage method, were particularly developed to suit the sub-1mW photovoltaic energy harvesting applications. The MPPT energy model has been developed and verified against both SPICE simulation and implemented prototypes. Both indoor light and thermoelectric energy harvesting methods proposed in this thesis have been implemented into prototype devices. The improved indoor light energy harvester prototype demonstrates 81% MPPT conversion efficiency with 0.5mW input power. This important improvement makes light energy harvesting from small energy sources (i.e. credit card size solar panel in 500lux indoor lighting conditions) a feasible approach. The 50mm × 54mm thermoelectric energy harvester prototype generates 0.95mW when placed on a 60oC heat source with 28% conversion efficiency. Both prototypes can be used to continuously power WSN for building energy management applications in typical office building environment. In addition to the hardware development, a comprehensive system energy model has been developed. This system energy model not only can be used to predict the available and consumed energy based on real-world ambient conditions, but also can be employed to optimize the system design and configuration. This energy model has been verified by indoor photovoltaic energy harvesting system prototypes in long-term deployed experiments.

Characterization of the degradation of wild-type and mutant HFE proteins during stress signalling in the endoplasmic reticulum

HFE is a transmembrane protein that becomes N-glycosylated during transport to the cell membrane. It acts to regulate cellular iron uptake by interacting with the Type 1 transferrin receptor and interfering with its ability to bind iron-loaded transferrin. There is also evidence that HFE regulates systemic iron levels by binding to the Type II transferrin receptor although the mechanism by which this occurs is still not well understood. Mutations to HFE that disrupt this function, or physiological conditions that decrease HFE protein levels, are associated with increased iron uptake, and its accumulation in tissues and organs. This is exemplified by the point mutation that results in conversion of cysteine residue 282 to tyrosine (C282Y), and gives rise to the majority of HFE-related hemochromatoses. The C282Y mutation prevents the formation of a disulfide bridge and disrupts the interaction with its co-chaperone β2-microglobulin. The resulting misfolded protein is retained within the endoplasmic reticulum (ER) where it activates the Unfolded Protein Response (UPR) and is subjected to proteasomal degradation. The absence of functional HFE at the cell surface leads to unregulated iron uptake and iron loading. While the E3 ubiquitin ligase involved in the degradation of HFE-C282Y has been identified, the mechanism by which it is targeted for degradation remains relatively obscure. The primary objective of this project was to further our understanding of how the iron regulatory HFE protein is targeted for degradation. Our studies suggest that the glycosylation status, and the active process of deglycosylation, are central to this process. We identified a number of additional factors that can contribute towards degradation and explored their regulation during ER stress conditions.