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.

Market-oriented new product development of health promoting foods for the ageing population

Major factors influencing food development and food marketing strategies in global market places at present can be attributable to the changing age structure of the population. The significant shifts in global age structure will inevitably lead to the number of people aged 60 reaching an all-time high of one billion by the year 2020. The rapidly growing population of ageing people globally represents a large, neglected and very much under-developed category within the Food Industry. The primary focus of this study was the integration of knowledge creation techniques at early NPD stages, for the development of market-oriented new health promoting foods for the ageing population. The methodology of this study was centered on an exploratory sequential mixed methods strategy. Stage one of the study involved in-depth semi-structured interviews with 16 Stakeholders to facilitate the need identification stage of the NPD process. The main outputs identified were the need for: the fortification of foods for a preventative nutrition approach, the development of foods that targeted age-related conditions such as cognitive, heart, gut and bone health, the integration of ageing compensatory packaging adaptations and the creation of marketing messages with an active lifestyle message. Stage two consisted of a market-oriented computer assisted NPD technique, a user centered design interaction (UCD) to integrate consumers as co-creators throughout the idea generation stage of the NPD process. The most important product attributes identified in this stage included: products targeted at brain and cognitive health, liquid based beverages, easy to use packaging with environmentally friendly elements, simplistic marketing with a clear focus on health not age and realistic health claims constructed with consumer friendly terminology. Finally, Stage three used an abbreviated means-end chain (MEC) analysis to complete the concept development stage of the NPD process. This stage identified commercial information that could be used by food firms for the development of positioning and communication strategies. Equally, the information generated could be of high strategic importance to governments, policy makers, health professionals and medical professionals. The values and goals listed in this stage included: better overall health, active lifestyle, optimum nutrition and wellbeing feelings. Overall, this research illustrated that knowledge creation techniques can assist firms in the development of market-oriented health promoting foods for the ageing population.