Embedding small wireless sensors into the environment allows for monitoring physical processes with high spatio-temporal resolutions. Today, these devices are equipped with a battery to supply them with power. Despite technological advances, the high maintenance cost and environmental impact of batteries prevent the widespread adoption of wireless sensors. Battery-free devices that store energy harvested from light, vibrations, and other ambient sources in a capacitor promise to overcome the drawbacks of (rechargeable) batteries, such as bulkiness, wear-out and toxicity. Because of low energy input and low storage capacity, battery-free devices operate intermittently; they are forced to remain inactive for most of the time charging their capacitor before being able to operate for a short time. While it is known how to deal with intermittency on a single device, the coordination and communication among groups of multiple battery-free devices remain largely unexplored. For the first time, the present thesis addresses this problem by proposing new methods and tools to investigate and overcome several fundamental challenges.

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Balises are transponders installed in railways. These devices are nowadays powered by means of a radiofrequency signal emitted by each running train that passes above them. It is only during this moment that the health state of the balises is checked. Hence, there is currently no way to check whether the balises are properly working before the train passes by them. With the aim of executing regular health checks to the balises, an additional source of energy to monitor the balises should be contemplated. Energy harvesting is observed as a suitable solution for this issue. However, a lack of suitability studies is contemplated which englobes the available energy harvesting solutions in railway environments. Therefore, this thesis presents an exploratory work that uses the health monitoring of the balises as a test case for the study of the compatibility of different energy harvesters in diverse railway environments. Hazardous and remote areas are identified as locations of interest for the implementation of the technology, as cabling in those areas is costly and health checks to balises that are not constantly active are of outmost interest. Thus, the addition of wireless communication networks is also studied, due to the need of sending the information obtained in the health checks to monitoring control units. After an initial research study is performed, requirements in railway environments are defined, and three railway scenarios are selected for a suitability study. Then, the investigated energy harvesters and wireless communication networks are compared analytically, and possible technologies for the storage of the harvested energy are presented. It is found that no energy harvester exists that suits all the environments and shows a sufficient power output to make constant checks in remote areas. Nonetheless, piezoelectric and wind harvesters are proposed, because of the commercial availability of the former and the potential of the latter. In terms of wireless communication networks, LoRaWAN shows a low power consumption, while it offers a wide communication range and global coverage. It is, therefore, proposed as the best framework for the wireless communication networks. / Baliser är transpondrar installerade i järnvägar. Dessa enheter drivs numera med hjälp av en radiofrekvenssignal som sänds ut av varje tåg som passerar ovanför baliserna. Det är först i detta ögonblick som balises hälsotillstånd kontrolleras. Därför finns det för närvarande inget sätt att kontrollera om baliserna fungerar korrekt innan tåget passerar dem. I syfte att utföra regelbundna hälsokontroller på baliserna bör en ytterligare kraftkälla för att övervaka baliserna övervägas. Energy harvesting observeras som en lämplig lösning för denna fråga. Det råder dock brist på lämplighetsstudier som förenar de tillgängliga energy harvesting lösningarna i järnvägsmiljöer. Därför presenterar denna avhandling ett undersökande arbete som använder hälsoövervakningen av baliserna som ett testfall för att studera kompatibiliteten hos olika energiskördare i olika järnvägsmiljöer. Farliga och avlägsna områden identifieras som platser av intresse för genomförandet av tekniken, eftersom kablar i dessa områden är kostsamma och hälsokontroller till baliser som inte ständigt är aktiva är av yttersta intresse. Således studeras också tillägget av trådlösa kommunikationsnätverk på grund av behovet av att skicka den information som erhållits vid hälsokontrollerna till övervakningskontrollområdena. Efter att en inledande forskningsstudie genomförts definieras krav i järnvägsmiljöer och tre järnvägsscenarier väljs ut för en lämplighetsstudie. Sedan jämförs de undersökta energiskördarna och trådlösa kommunikationsnätverk analytiskt, och eventuell teknik för lagring av den skördade energin presenteras. Det konstateras att det inte finns någon energiskördare som passar alla miljöer och visar en tillräckligt effekt för att göra konstanta kontroller i avlägsna områden. Ändå föreslås piezoelektriska och vindskördare på grund av den förstnämnda kommersiella tillgänglighet och den senare potentialen. När det gäller trådlösa kommunikationsnätverk visar LoRaWAN en låg strömförbrukning, medan det erbjuder ett brett kommunikationssortiment och global täckning. Det föreslås därför som den bästa ramen för de trådlösa kommunikationsnäten.

<p>We examine energy harvesting sensor networks, more specifically, a sensor network using the Geographic Routing with Environmental Energy Supply (GREES) algorithm. We start with a discussion of other sources of energy conservation both in energy harvesting and non-energy harvesting sensor networks. Ideas presented in these works are combined where possible with the GREES algorithm. A sensor network was actually built to test and (if possible) improve the algorithm. There were problems along the way, but they were overcome to produce a functioning energy harvesting sensor network that used solar cells as the energy harvesting unit. Tests were run on the network by giving a consistent light and battery supply, and then changing parameters of the algorithm to see their effect on the lifetime of the network, indicating the network's sensitivity to individual parameters. These results are presented, along with their interpretation, as well as an error analysis detailing the behaviour of the algorithm. We discuss how sensitive the network is to each parameter, indicating which parameters are more important to calibrate or measure correctly.</p> / Master of Applied Science (MASc)

The resilience of power infrastructure against environmental challenges, particularly wind-induced vibrations, is crucial for ensuring the reliability and longevity of overhead power lines. This dissertation extends the development of the Mobile Damping Robot (MDR) as a novel solution for mitigating wind-induced vibrations through adaptive repositioning and energy harvesting capabilities. Through comprehensive experimental and numerical analyses, the research delineates the design, optimization, and application of the MDR, encompassing its dynamic adaptability and energy harvesting potential in response to varying wind conditions. The study begins with the development and validation of a linearized model for the MDR, transitioning to advanced nonlinear models that more accurately depict the complex interactions between the robot, cable system, and environmental forces. A global stability analysis provides crucial insights into the operational limits and safety parameters of the system. Further, the research explores a multi-degree-of-freedom system model to evaluate the MDR's efficacy in real-world scenarios, emphasizing its energy harvesting efficiency and potential for sustainable operation. Findings from this research show the clear promise for the development of the MDR with the consideration of the nonlinear dynamics in play between the robot, the cable, and the wind. This work lays a foundational framework for future innovations in infrastructure maintenance, paving the way for the practical implementation of mobile damping technologies in energy systems. / Doctor of Philosophy / Across the United States, over 160,000 miles of power lines crisscross the landscape, powering everything from small homes to large industrial complexes. These critical infrastructures, however, are constantly battered by the elements, particularly by strong winds capable of inducing Aeolian vibrations. Such vibrations lead to oscillations in the power lines due to wind forces, potentially causing severe structural damage, compromising public safety, and incurring considerable economic costs. In response to these challenges, various mitigation strategies have been employed. Traditional methods include regular inspections carried out by foot patrols, helicopters, or sophisticated inspection robots, though these approaches are notably resource-intensive and costly. Additionally, mechanical devices like Stockbridge dampers are utilized to dampen the vibrations, but they suffer from efficiency issues when misaligned with the vibration nodes. This dissertation extends the study to an innovative solution to overcome these limitations: a mobile damping robot designed to navigate along power lines and autonomously position itself at the points of highest vibration amplitude, thereby optimizing vibration dampening. This study delves into the feasibility and effectiveness of such a solution, supported by thorough numerical simulations. The aim is to demonstrate how this advanced approach could redefine maintenance strategies for power lines, enhancing their resilience against wind-induced vibrations and reducing the reliance on laborious inspection methods and static damping devices with limited efficiency.

This study deals with a general method for the analysis of a semi-active control technique for a fast-shunt switching system. The benefit of the semi-active system is the reduction in power consumption, which is a significant disadvantage of a fully active system compared with a passive system. A semi-active system under consideration is a semi-actively shunted piezoelectric system, which converts the strain energy into electrical energy through strong electromechanical coupling achieved though the piezoelectric phenomenon. Our proposed semi-active approach combines a PZT-based energy harvesting with a fast switching system driven by a Pulse-Width Modulated (PWM) signal. The fast switching system enables continuous adaptation of vibration energy control/harvesting by varying the PWM duty cycle. This contrasts with a conventional capacitance switching system that can only change the capacitance at discrete values. The analysis of the current piezoelectric system combined with a fast-switching system poses a considerable challenge as it contains both continuous and discrete characteristics. The study proposes an enhanced averaging method for analyzing the piecewise linear system. The simulation of the averaged system is much faster than that of the time-varying system. Moreover, the analysis derives error bounds that characterize convergence in the time domain of the averaged system to the original system. The dissertation begins with the derivation of the equations governing the physics of a piezostructure combined with an electrical switching shunt network. The results of the averaging analysis and numerical simulation are presented in order to provide a basis for estimating the structural responses that range between open- and short-circuit conditions which constitutes two limiting conditions. An experimental study demonstrates that the capacitive shunt bimorph piezostructure coupled with a single switch can be adjusted continuously by varying the PWM duty cycle. And the behavior of such hybrid system can be well predicted by the averaging analysis. / Ph. D.

Low-grade heat, either in the form of waste heat or natural heat, represents an extremely promising source of renewable energy. A cost-effective method for recovering the low-grade heat will have a transformative impact on the overall energy scenario. Efficiency of heat engines deteriorates with decrease in hot-side temperature, making low-grade heat recovery complex and economically unviable using the current state-of-the-art technologies, such as Organic Rankine cycle, Kalina cycle and Stirling engine. In this thesis, a fundamental breakthrough is achieved in low-grade thermal energy harvesting using thermomagnetic and thermoelectric effects. This thesis systematically investigates two different mechanisms: thermomagnetic effect and thermoelectric effect to generate electricity from the low-grade heat sources available near ambient temperature to 200°C. Using thermomagnetic effect, we demonstrate a novel ultra-low thermal gradient energy recovery mechanism, termed as PoWER (Power from Waste Energy Recovery), with ambient acting as the heat sink. PoWER devices do not require an external heat sink, bulky fins or thermal fluid circulation and generate electricity on the order of 100s μW/cm3 from heat sources at temperatures as low as 24°C (i.e. just 2°C above the ambient) to 50°C. For the high temperature range of 50-200°C, we developed the unique low fill fraction thermoelectric generators that exhibit a much better performance than the commercial modules when operated under realistic conditions such as constant heat flux boundary condition and high thermally resistive environment. These advancements in thermal energy harvesting and waste heat recovery technology will have a transformative impact on renewable energy generation and in reducing global warming. / PHD / Energy is essential to life. While most living organisms utilize natural resources directly to meet their energy requirements, humans need electricity. Unarguably, electricity has made our lives easy; however, it is an expensive form of energy. Every year, a tremendous amount of fossil fuels is burnt to meet the ever-growing energy demand. While we are concerned due to the escalating energy prices, depleting fossil resources, and negative environmental impact, it is devastating to know that more than half of the useable energy generated from various renewable and non-renewable sources are ultimately discarded to atmosphere as byproduct, mostly in form of wasted heat. Utilizing waste heat, particularly when it occurs at low temperature, is usually complex and cost-ineffective. A cost-effective method for recovering the low-grade heat will have a transformative impact on the overall energy scenario. In this thesis, a fundamental breakthrough is achieved in developing the new/improved thermal energy harvesting methods to generate electricity from low-grade heat.

As human dependence on electronic devices grows, there is an emerging need on finding sustainable power sources for low power electronics and sensors. One of the promising possibilities in this space is the human body itself. Harvesting significant power from daily human activities will have a transformative effect on wearables and implantables. One of the main challenges in harvesting mechanical energy from human actions is to ensure that there is no effect on the body itself. For this reason, any intrusive mechanism will not have practical relevance. In this dissertation, novel non-intrusive energy harvesting technologies are investigated that can capture available energy from body, motion, and surroundings. Energy harvesting from the body is explored by developing a wrist-based thermoelectric harvester that can operate at low-temperature gradients. Energy harvesting from motion is investigated by creating a backpack and shoe sole. These devices passively store kinetic energy in a spring that is later released to a generator when it is not intrusive to the user kinematics. Lastly, energy harvesting from immediate surroundings is investigated by designing a two degree of freedom vibration absorber that is excited by electromagnetic fields found in common household appliances. These novel solutions are shown to provide consistent electrical power from wasted energy. Harvester designs are extensively modeled and optimized device architectures are manufactured and tested to quantify the relevant parameters such as output voltage and power density. / Doctor of Philosophy / Energy harvesting is the action to transform energy in the form of heat, relative motion, light, etc. into useful electrical energy. An example of an energy harvester is a solar cell which converts energy in the form of light to electricity. Our body consumes a considerable amount of energy to maintain our body temperature and achieve everyday movements, i.e., walking, jumping, etc. The purpose of this research was to fabricate, model and test wearable energy harvesters in the form of a backpack, a shoe sole, a watch, and a cantilever beam to charge mobile electronics on the go. Electrical energy is harvested from human motion by using the relative displacement between the human torso and a payload. Similarly, the ankle joint is used to produce electricity by using the relative rotation between the foot and shank. The difference in temperature between the ambient air and the human body is used to generate enough electricity to power a wrist watch. Finally, energy is harvested from everyday surroundings by using a cantilever beam which absorbs magnetic fields coming from power cords and able to power sensors.