Tesis sobre el tema "Harvesting"

This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

Ubiquitous computing and pervasive networks are prevailing to impact almost every part of our daily lives. Convergence of technologies has allowed electronic devices to become untethered. Cutting of the power-cord and communications link has provided many benefits, mobility and convenience being the most advantageous, however, an important but lagging technology in this vision is the power source. The trend in power density of batteries has not tracked the advancements in electronic systems development. This has provided opportunity for a bridging technology which uses a more integrated approach with the power source to emerge, where a device has an onboard self sustaining energy supply. This approach promises to close the gap between the increased miniaturisation of electronics systems and the physically constrained battery technology by tapping into the ambient energy available in the surrounding location of an application. Energy harvesting allows some of the costly maintenance and environmentally damaging issues of battery powered systems to be reduced. This work considers the characteristics and energy requirements of wireless sensor and actuator networks. It outlines a range of sources from which the energy can be extracted and then considers the conversion methods which could be employed in such schemes. This research looks at the methods and techniques for harvesting/scavenging energy from ambient sources, in particular from the motion of human traffic on raised flooring and stairwells for the purpose of powering wireless sensor and actuator networks. Mechanisms for the conversion of mechanical energy to electrical energy are evaluated for their benefits in footfall harvesting, from which, two conversion mechanisms are chosen for prototyping. The thesis presents two stair-mounted generator designs. Conversion that extends the intermittent pulses of energy in footfall is shown to be the beneficial. A flyback generator is designed which converts the linear motion of footfall to rotational torque is presented. Secondly, a cantilever design which converts the linear motion to vibration is shown. Both designs are mathematically modelled and the behaviour validated with experimental results & analysis. Power, energy and efficiency characteristics for both mechanisms are compared. Cost of manufacture and reliability are also discussed.

Improvements in embedded electronics which have effectively reduced power consumption requirements as well as advancements in IC technology allowing utilization of low power inputs have made Energy Harvesting a popular power solution for low power applications such as WSNs. In many implementation areas, we can see solar, thermal, and vibration energy harvesting techniques have taken the role of batteries as power source. Now that Energy Harvesting is a popular and considerably mature technology, with proper design and installation, any object exposing energy has the ability to be promoted as a power source. We are currently living in Internet age where we connect to the world through network packets. Ethernet, by far, is the most popular LAN technology which allows us to plug and play. Therefore, on an Ethernet link, billions of packets where our data are encapsulated in are traversing every hour. We assume each of these packets exposes some level of energy on an Ethernet link. The challenge here is harvesting the energy available from Ethernet packets and transforming it into useful energy so that it can be used to power devices such as WSNs. In this thesis work, we have revealed how much energy is available from Ethernet packets, and how much of it can be made usable. We have also designed a system where a WSN is generating all of its operating power solely from Ethernet packets and consuming this energy in communication with a base station.

The concept of harvesting electrical energy from ambient vibration sources has been a popular topic of research in recent years. The motivation behind this research is largely due to recent advancements in microelectromechanical systems (MEMS) technology - specifically the construction of small low powered sensors which are capable of being placed in inaccessible or hostile environments. The main drawback with these devices is that they require an external power source. For example, if one considers large networks of low powered sensors (such as those which may be attached to a bridge as part of a structural health monitoring system) then one can envisage a scenario where energy harvesters are used to transfer the vibration energy of the bridge into electrical energy for the sensors. This would alleviate the need for batteries which, in this scenario, would be difficult to replace. Initial energy harvester designs suffered from a major flaw: they were only able to produce useful amounts of power if they were excited close to their resonant frequency. This narrow bandwidth of operation meant that they were poorly suited to harvesting energy from ambient vibration sources which are often broadband and have time dependent dominant frequencies. This led researchers to consider the concept of nonlinear energy harvesting - the hypothesis that the performance of energy harvesters could be improved via the deliberate introduction of dynamic nonlinearities. This forms the main focus of the work in this thesis. The first major part of this work is concerned with the development of an experimentally validated physical-law based model of an electromagnetic energy harvester with Duffing-type nonlinearities. To this end, a self-adaptive differential evolution vi (SADE) algorithm is used in conjunction with experimental data to estimate the parameters needed to accurately model the behaviour of the device. During this investigation it is found that the response of the energy harvesting device in question is very sensitive to the effects of friction. Consequently, a detailed study is undertaken with the aim of finding whether the model performance could be improved by accounting for this complex nonlinear phenomenon. After investigating several different friction models, a reliable and extensively validated digital model of a nonlinear energy harvesting device is realised. With the appropriate equations of motion identified, analytical approximation methods are used to analyse the response of the device to sinusoidal excitations. The motivation for the second main part of this work arises from the fact that ambient excitations are often stochastic in nature. As a result, much of the work in this section is directed towards gaining an understanding of how nonlinear energy harvesters respond to random excitations. This is an interesting problem because, as a result of the random excitation, it is impossible to say exactly how such a device will respond - the problem must be tackled using a probabilistic approach. To this end, the Fokker-Planck-Kolmogorov (FPK) equation is used to develop probability density functions describing how the nonlinear energy harvester in question responds to Gaussian white noise excitations. By conducting this analysis, previously unrecognised benefits of Duffing-type nonlinearities in energy harvesters are identified along with important findings with regards to device electrical optimisation. As for friction effects, the technique of equivalent linearisation is employed alongside known solutions of the FPK equation to develop expressions approximating the effect of friction on randomly excited energy harvesters. These results are then validated using Monte-Carlo methods thus revealing important results about the interaction between Duffing-type and friction nonlinearities. Having investigated sinusoidal and random excitations, the final part of this work focuses on the application of nonlinear energy harvesting techniques to real energy harvesting scenarios. Excitation data from human walking motion and bridge vibrations is used to excite digital models of a variety of recently proposed nonlinear energy harvesters. This analysis reveals important information with respect to how well energy harvesting solutions developed under the assumption of Gaussian white noise excitations can be extended to real world scenarios.

Vibration measurements conducted in three vehicles windshields are used to determine frequency content in the windshield of moving vehicles. A piezoelectric energy harvester is modeled, and used in simulations to determine output voltage and power with measured acceleration signal as input.

Developing resilient sensor systems for deployment in extreme environments is a challenge which silicon carbide, along with other wide band gap materials, stands to play a major role in. However, any system developed will be hindered in its usefulness unless the problem of providing a power supply in these extreme conditions is addressed. This work addresses this need; a wireless sensor node conceived of standard o the shelf components was first developed and used as the basis for the design considerations required for a silicon carbide sensor node. The silicon system developed uses a piezoelectric energy harvester for the power supply and exhibits favourable operating characteristics for low vibration environments. It is capable of continuous operation at 120 mg (1.177 ms⁻²) and at 40 mg operates with a system duty cycle of 0.05. PZT, a standard piezoelectric energy harvesting material, was characterised to 300°C to test its resilience to the conditions found in hostile environments. The material degrades considerably with temperature, with a decrease in Youngs modulus from 66 GPa at room temperature to 8.16 GPa at 300 C. The room temperature value is repeatable once cooled with an observed hysteresis in the upper temperature range. The peak output voltage at resonance also varies with temperature, resulting in an 11.6% decrease in room temperature voltage once the device is heated to 300°C. The output voltage at 300°C is found to be 2.05 V, a considerable decrease from the initial 11.1 V output at room temperature. The decrease in voltage with temperature is not monotonic as maybe expected, the data showing that at 473 K there is an increase in output voltage which is caused by a decrease in mechanical damping. SiC pin diodes were fabricated with wide drift regions to promote a large depletion width, in order to maximise the capture cross section of incident light on the devices. The large drift region produces a high series resistance. However, ll factors above 0.7 show that the device is not signi cantly a ected. SiC is shown to be an e ective UV harvester with an observed increase in output power from 0.17 mWcm⁻² at room temperature to 0.32 mWcm⁻² at 600 K. Fill factor also remains stable with temperature, indicating that the device is not a ected by variation in parameters such as shunt and series resistances or the ideality factor. There are current technological di culties which preclude the manufacture of large area silicon carbide solar cells and as such, an alternative networking solution is presented as a way to increase the output power of the devices. Given that these devices would be subject to long term high temperature exposure, a 700 hour thermal stress test is carried out at 450°C to explore the failure mechanism of the devices. There is an observed decrease in device ll factor which indicates that the device su ers increasing degradation. The data shows that this is caused by increasing series resistance, which reduces the devices ability to output power. SEM imaging and SIMS analysis show this is likely caused by signifcant metal diusion in the contact stack which could potentially be overcome by the addition ofan alternative di usion barrier. Once energy is generated by an energy harvester is must be stored so that it can be used when required. To this end both substrate and on chip storage technologies are discussed in the forms of AlN and HfO₂ metal insulator metal (MIM) capacitors. To test the feasibility of both solutions, AlN and HfO₂ MIM capacitors were characterised to 300°C. The HfO₂ device leakage has a strong temperature dependence as observed in the IV characteristics and the capacitance density does not scale according to parallel plate theory. However, the devices can be e ectively networked and their leakage reduced with series connection. The internal voltage decay of the device is reduced with series connection, due to the di er-ing work functions of the metal-insulator contacts. The alternative AlN solution exhibits substantially weaker temperature dependance and signi cantly improved lm quality. The data shows no existence of a barrier at the insulator - metal interface, as observed in the HfO2 device IV characteristics. The extracted activation energy is stable with temperature at 1.26 +/- 0.15 eV indicating a trap assisted leakage mechanism. This method is more suitable to fabrication of large area storage as it can be fabricated o chip on a less expensive substrate and the devices fabricated exhibit a higher yield than the HfO₂ devices.

In this work, we were motivated to develop novel devices for water harvesting inspired by natural trees, and to understand their collection efficiency and working principles. We accomplished that with scale-model and large-scale fog harps, floating leaves, and synthetic trees. Fluids mechanics, physics, and thermodynamics were applied to solve the problems and rationalize the results. Redwood-inspired fog harps were designed with stainless steel vertical wires, using 3D-printing and laser-cutting techniques. Fog harps always harvested more water than any of the meshes, tested both under heavy fog and light fog conditions. The aerodynamic efficiency, deposition efficiency, and sliding efficiency were calculated to compare the fog harvesting performance. These findings provide insight into the new design of fog harvesters with high-efficiency fog harvesting performance, and future development of large fog harps, applied into regions even with light fog conditions, as an economically viable means. synthetic trees were fabricated with a nanoporous ceramic disk and silicone tubes. This tree system was tested in an environmental chamber (6 cm short trees) or a plant growth chamber (3m tall trees), both with controlled ambient humidities. The system pressure was calculated with Darcy's equation, Poiseuille equation and Laplace equation. The stable transpiration can happen to any scalable tree, which pumps water up an array of large tubes. Our synthetic trees, like natural trees, have the ability to lift water across a wide range of water temperatures and ambient humidities. They can be used as the large-scale evaporation-driven hydraulic pump, for example, pumped storage hydropower, filtration, underground water extraction.
Doctor of Philosophy
The purpose of this work is to investigate and characterize novel techniques for water harvesting that are inspired by natural trees. We are interested in two modes of water harvesting in particular: fog harps and synthetic trees. Fog harps were comprised of only vertical wires, inspired by the parallel structures of redwoods, which can capture and shed off fog droplets efficiently. Fog harps harvested more water than the traditional mesh nets, both under heavy fog and light fog conditions. Redwood-inspired fog harps have the high-efficient fog harvesting performance. They can be set up at coastal deserts to collect water from fog, where there is scarce rainfall but plenty of fog, like Chile, Peru and South Africa. Synthetic trees were designed with nanoporous disk (leaf) and tubes (xylem conduits), inspired by the transpiration process in natural trees. This transpiration-powered pump can lift water against the gravity at large scales, driven by the water evaporating from the nanopores. They can be used as the large-scale evaporation-driven hydraulic pump, for example, pumped storage hydropower, filtration, underground water extraction.

Thesis (M.Sc. (Plant Production)) -- University of Limpopo, 2014
Wild medlar (Vangueria infausta subsp. infausta) is a popular indigenous fruit available and consumed by rural communities in Limpopo Province, South Africa. Inadequate post-harvest practices in indigenous fruit plants including V. infausta fruit forms major constrains in expanding their production. There is scanty information documented on neither objective nor subjective harvesting indices of indigenous fruit plants consumed by locals in sub-Saharan Africa. Thus, the objective of this study was to determine the effect of harvesting time on physico-chemical properties and selected nutritional composition of V. infausta fruit. Fruits were harvested twice, where two harvesting times were regarded as treatments and each tree as replication. The reduction for fruit weight, sugar content and sugar/acid ratio was highly significant (P ≤ 0.05), whereas for average fruit diameter, seed weight, acid ratio and pH content this may imply that the listed parameters are treatment which was non-significant (P ≤ 0.05). The treatment reduced P, K, Mn and Fe by 33%, 18%, 3% and 7%, respectively. On the other hand, treatments had no effect on N and Ca. The reduction of phosphorus was highly significant (P ≤ 0.05), whereas for N, K, Ca, Mn and Fe treatment impact was non-significant (P ≤ 0.05). Similarly, the treatment consistently reduced moisture content and increased dry matter and crude protein of V. infausta by 76%, 300% and 7%, respectively. The reduction of moisture content, increase in dry matter was highly significant (P ≤ 0.05), whereas crude protein treatment impact was non-significant (P ≤ 0.05). The data indicated that the best time to harvest V. infausta fruit was during January when fruits were cosmetically appealing and not wrinkled. This study demonstrated that there was less variation in some measured objective harvesting indices of V. infausta fruit harvested at two harvesting time. More work would be required to do physico-chemical properties and selected mineral elements analysis from wide growth habitat for conclusive recommendations.

Every marine energy source presents advantages and disadvantages. For example, they are not atthe same stage of maturity. Tidal range power is fully mature but the limited number of sitesavailable, combined with the large environmental impacts and investment costs limit itsdevelopment. The idea of artificial lagoons that will be offshore tidal range plant could create a newinterest for this technology. But for the moment, no plant of this type has been constructed yet. Tidalstream power is the next mature technology of marine energy after tidal range. Its development willrequire public subsidies but is supposed to be commercial in 2015. Systems are already indemonstration in several countries (UK, France and Canada). Wave power is less mature but it willbenefit from the development of tidal stream power and will probably be commercial in 2020. Somesystems are also in demonstration but challenges seem greater in wave power than in tidal power.Wave power conversion systems have to extract energy from the waves, even the largest ones, butat the same time resist to them. Contrary to tidal stream which has a predictable resource, waves areway less predictable and systems will have to be able to resist and valorize waves. OTEC (OceanThermal Energy Conversion) has been studied for years but it is still not mature. Its development forelectricity production needs technology research to develop cheaper and more compact systems(heat exchangers, pipes…). Air conditioning applications are developing and also require the use ofpipes and heat exchangers. Advances in this utilization could maybe help the development of OTECsystems for electricity production. Osmosis is the less mature and the most challenging technology. Atechnological breakthrough in the membrane could allow a rapid development. This breakthroughwill probably come from other sectors so it is important for the industries to get ready in order todevelop the system as soon as this technological improvement will be made.

Wireless micro-sensors can enjoy popularity in biomedical drug-delivery treatments and tire-pressure monitoring systems because they offer in-situ, real-time, non-intrusive processing capabilities. However, miniaturized platforms severely limit the energy of onboard batteries and shorten the lifespan of electronic systems. Ambient energy is an attractive alternative because the energy from light, heat, radio-frequency (RF) radiation, and motion can potentially be used to continuously replenish an exhaustible reservoir. Of these sources, solar light produces the highest power density, except when supplied from indoor lighting, under which conditions the available power decreases drastically. Harnessing thermal energy is viable, but micro-scale dimensions severely limit temperature gradients, the fundamental mechanism from which thermo piles draw power. Mobile electronic devices today radiate plenty of RF energy, but still, the available power rapidly drops with distance. Harvesting kinetic energy may not compete with solar power, but in contrast to indoor lighting, thermal, and RF sources, moderate and consistent vibration power across a vast range of applications is typical. Although operating conditions ultimately determine which kinetic energy-harvesting method is optimal, piezoelectric transducers are relatively mature and produce comparatively more power than their counterparts such as electrostatic and electromagnetic kinetic energy transducers. The presented research objective is to develop, design, simulate, fabricate, prototype, test, and evaluate CMOS ICs that harvest ambient kinetic energy in periodic and non-periodic vibrations using a small piezoelectric transducer to continually replenish an energy-storage device like a capacitor or a rechargeable battery. Although vibrations in surrounding environment produce abundant energy over time, tiny transducers can harness only limited power from the energy sources, especially when mechanical stimulation is weak. To overcome this challenge, the presented piezoelectric harvesters eliminate the need for a rectifier which necessarily imposes threshold limits and additional losses in the system. More fundamentally, the presented harvesting circuits condition the transducer to convert more electrical energy for a given mechanical input by increasing the electromechanical damping force of the piezoelectric transducer. The overall aim is to acquire more power by widening the input range and improving the efficiency of the IC as well as the transducer. The presented technique in essence augments the energy density of micro-scale electronic systems by scavenging the ambient kinetic energy and extends their operational lifetime. This dissertation reports the findings acquired throughout the investigation. The first chapter introduces the applications and challenges of micro-scale energy harvesting and also reviews the fundamental mechanisms and recent developments of various energy-converting transducers that can harness ambient energy in light, heat, RF radiation, and vibrations. Chapter 2 examines various existing piezoelectric harvesting circuits, which mostly adopt bridge rectifiers as their core. Chapter 3 then introduces a bridge-free piezoelectric harvester circuit that employs a switched-inductor power stage to eliminate the need for a bridge rectifier and its drawbacks. More importantly, the harvester strengthens the electrical damping force of the piezoelectric device and increases the output power of the harvester. The chapter also presents the details of the integrated-circuit (IC) implementation and the experimental results of the prototyped harvester to corroborate and clarify the bridge-free harvester operation. One of the major discoveries from the first harvester prototype is the fact that the harvester circuit can condition the piezoelectric transducer to strengthen its electrical damping force and increase the output power of the harvester. As such, Chapter 4 discusses various energy-investment strategies that increase the electrical damping force of the transducer. The chapter presents, evaluates, and compares several switched-inductor harvester circuits against each other. Based on the investigation in Chapter 4, an energy-investing piezoelectric harvester was designed and experimentally evaluated to confirm the effectiveness of the investing scheme. Chapter 5 explains the details of the IC design and the measurement results of the prototyped energy-investing piezoelectric harvester. Finally, Chapter 6 concludes the dissertation by revisiting the challenges of miniaturized piezoelectric energy harvesters and by summarizing the fundamental contributions of the research. With the same importance as with the achievements of the investigation, the last chapter lists the technological limits that bound the performance of the proposed harvesters and briefly presents perspectives from the other side of the research boundary for future investigations of micro-scale piezoelectric energy harvesting.

Approved for public release; distribution is unlimited
The U.S. Navy has many opportunities to take advantage of energy sources that are usually wasted because these low power sources yield such low-voltages that a normal voltage converter is not efficient enough to harvest the energy. Low-voltage energy is available in many forms including solar, thermal, vibration, and electro-magnetic. The power that can be obtained from these sources on a small scale can be taken advantage of by using an ultra-low power boost converter that is specifically designed for energy harvesting applications. These energy sources with a very small footprint can be used in military and defense applications such as wireless sensor networks, industrial monitoring, and varieties of portable and wearable devices. The theory of power conversion, synchronous rectification, and maximum power point tracking is discussed. A discussion of the benefits of using an energy converter made specifically for energy harvesting is also covered. A commercially available energy harvester converter is simulated using a simulation program with integrated circuit emphasis, and a solar application is tested with hardware. The hardware experiments explore the startup sequence of the circuit, the switching profile of the converter, and a test of the circuits efficiency.

This thesis presents novel research in the area of energy harvesting from broadband vibra-tions. The aim of energy harvesting is to recover energy wasted or unused in the environmentto power low-consumption devices on the order of hundreds of microwatts to milliwatts. The motivation is twofold. In providing a localized, self-contained power source, device reliability, flexibility of installation location can be improved, and maintenance costs can be reduced. Furthermore, reduced reliance on batteries will mitigate the environmental impact associated with resource extraction, and disposal. To this end, this thesis investigates bistable laminates with piezoelectric transduction as broadband energy harvesters. Hitherto, a wealth of literature exists in which narrowband energy harvesters have been studied and optimized to operate over a small frequency interval. While these have been successful to the point of having devices commercially available, many situations exist where the dominant frequencies from which energy is to be harvested change with respect to time, or may be dominated by noise, thus not having a truly dominating frequency. Energy harvesters with nonlinear frequency responses have attracted substantial research interest because of their ability to respond over a broaderfrequency band. Due to complexities of the response of these harvesters, particularly when the intensity of the vibrational input is high, modeling their behavior is difficult. Designing these harvesters is therefore challenging as the relationships between the various design parameters and power output can be highly involved, or require numerical solutions as analytical solutions may not be possible. This thesis helps to address this knowledge gap. Bistable laminates ofboth cantilever and plate configuration are studied. Parametric studies are undertaken to empirically demonstrate the relationship between power output and parameters such as resistance load, proof mass addition, operation orientation, different shapes, ply angles, and introduction of adjustable magnetic compression. Modeling work is also undertaken to capture the mainfeatures of the nonlinear response such as subharmonics, superharmonics, and snap-through. A study is also carried out to quantify the differences of performance between a linear harvester and an equivalent bistable counterpart. As a practical demonstration, some plate-type harvesters are subjected to excitation patterns based on measured train data. Ultimately, thisthesis provides an in depth understanding of bistable shape, layup, and design on harvesting performance.

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.
Includes bibliographical references (p. 81-83).
Despite advances in search technology, few software systems have been developed which accurately categorize multimedia files. The most successful systems for searching images, sounds, or movies rely on keyword annotation to provide meaningful search terms for non-text documents. Unfortunately, such systems usually require the author to enter the keywords manually, a task that is commonly neglected, or is executed poorly. This thesis proposes an approach to document categorization called Interaction Harvesting, wherein systems establish document relationships based on organizational and curatorial cues, harvested from the mouse and click gestures of an online community. Specifically, the spatial and temporal proximity and placement of documents are taken as indicators of document similarity. We propose an expansion technique whereby such proximal documents exert weighted keyword influences on each other. We hypothesize that these approaches will form a document classification framework that relieves some of the difficulty of the annotation process, while providing keyword-equivalent retrieval performance.
by Noah S. Fields.
S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-120).
Efficient mechanical energy harvesters enable various wearable devices and may also act as auxiliary energy supply to isolated area. In this thesis, I present a novel class of mechanical energy harvesters based on stress-voltage coupling in electrochemically alloyed electrodes. The device consists of two identical Li-alloyed Si as electrodes, separated by electrolyte-soaked polymer membranes. Bending-induced asymmetric stresses generate chemical potential difference, driving lithium ion flux from the compressed to the tensed electrode to generate electric current. Unbending the device reverses the ion flux, generating electrical current in the opposite direction. The thermodynamic analyses reveal that the ideal energy-harvesting efficiency of this device is dictated by the Poisson's ratio of the electrodes. For the thin-film-based energy harvester used in this study, the device has achieved the overall efficiency of 0.6% and a generating capacity of 15%. The device also presents unique characteristics over the existing type of mechanical energy harvesters. Compared to piezoelectric or triboelectric generators, the prototype demonstrates low internal impedance of the order of 300[omega] as opposed to 100M[omega] in the other two types, and continuous electric current of the order of 3 seconds as opposed to 50ms in the other two types. From kinetics analysis, we show that the device's electric current generation is limited by lithium diffusion inside the LixSi electrode for sufficiently thick electrodes and by electrolyte diffusion for thin electrodes below 400nm. Tuning the current peak widths between 5s and 22s was demonstrated experimentally. The framework developed in the kinetics analyses also suggests that the device may be used as a spectroscopic tool to measure lithium diffusivity inside electrochemical alloys. The experimentally observed kinetics suggests lithium diffusivity on the order of 10-¹⁰cm² /s in Li₃.₁Si. The device demonstrates a practical use of stress-composition coupling in electochemically active alloys to harvest low-grade mechanical energies from various lowfrequency motions, such as everyday human activities. The analyses present the quantitative strategies to optimize the device in terms of its total energy output, kinetic behavior and ultimately the design principles for an energy harvester optimized for harvesting a specifically targeted frequency motion.
by Sangtae Kim.
Ph. D.

The rapid advancement in complimentary metal-oxide-semiconductor (CMOS) electronics has led to a reduction in the sizes of wireless sensor networks (WSN) and a subsequent decrease in their power requirements. To meet these power requirements for long time of operation, energy harvesters have been developed at the micro scale which can convert vibration energy into electrical energy. Recent studies have shown that for mechanical-to-electrical conversion at the mm-scale (or micro scale), piezoelectric mechanism provides the best output power density at low frequencies as compared to the other possible mechanisms for vibration energy harvesting (VEH). However, piezoelectric-based VEH presents a fundamental challenge at the micro scale since the resonance frequency of the structure increases as the dimension decreases. Electromagnetic induction is another voltage generation mechanism that has been utilized for VEH. However, the electromagnetic induction based VEH is limited by the magnet and coil size and the decrease in power density at the micro scale. Hybrid energy harvesting is a novel concept that allows for increased power response and increased optimization of the generated voltage. The work in this field is currently limited due to integration challenges at small dimensions. An effective design for low frequency piezoelectric VEH is presented in this work. A unique cantilever design called arc-based cantilever (ABC) is presented which exhibits low natural frequencies as compared to traditional cantilevers. A general out-of-plane vibration model for ABCs was developed that incorporated the effects of bending, torsion, transverse shear deformation and rotary inertia. Different configurations of micro ABCs were investigated through analytical modeling and validation experiments. ABC structures were fabricated for dual-phase energy harvesting from vibrations and magnetic fields. Next, a levitation-induced electromagnetic VEH concept based on double-repulsion configuration in the moving magnet composite was studied. Computational modeling clearly illustrated the advantages of the double-repulsion configuration over the single-repulsion and no-repulsion configurations. Based on the modeling results, an AA battery-sized harvester with the double-repulsion configuration was fabricated, experimentally characterized and demonstrated to charge a cell phone. The scaling analysis of electromagnetic energy harvesters was conducted to understand the performance across different length scales. A micro electromagnetic harvester was developed that exhibited softening nonlinear spring behavior, thus leading to the finding of nonlinear inflection in magnetically-levitated electromagnetic harvesters. The nonlinear inflection theory was developed to show its causal parameters. Lastly, a coupled harvester is presented that combines the piezoelectric and electromagnetic voltage mechanisms. The advantages of each mechanism were shown to positively contribute to the performance of hybrid harvester. The cantilever provided low stiffness, low frequency, and pure bending, while the magnetic system provided nonlinearity, broadband response, and increased strain (and thus voltage).
Ph. D.

Scholars in science and technology studies have long been concerned with a variety of issues revolving around technological change, such as explaining the origins of technological innovation and arguing for or against technological determinism. This thesis reviews a number of theoretical models developed by historians, philosophers, sociologists, and other scholars to explain technological change. A case study of technological innovations in industnal forestry and timber harvesting practices provides a basis for a critique of these previously proposed models and for an argument for a new model. This model, an ecological model, suggests homeostatic pressures play a major role in the innovative processes within any technological system.
Master of Science

Energy harvesting technology has the ability to create autonomous, self-powered electronic systems that do not rely on battery power for their operation. The term energy harvesting describes the process of converting ambient energy surrounding a system into useful electrical energy through the use of a specific material or transducer. A widely studied form of energy harvesting involves the conversion of mechanical vibration energy into electrical energy using piezoelectric materials, which exhibit electromechanical coupling between the electrical and mechanical domains. Typical piezoelectric energy harvesting systems are designed as add-on systems to a host structure located in a vibration rich environment. The added mass and volume of conventional vibration energy harvesting designs can hinder to the operation of the host system. The work presented in this dissertation focuses on advancing piezoelectric energy harvesting concepts through the introduction of multifunctionality in order to alleviate some of the challenges associated with conventional piezoelectric harvesting designs.

The concept of multifunctional piezoelectric self-charging structures is explored throughout this work. The operational principle behind the concept is first described in which piezoelectric layers are directly bonded to thin-film battery layers resulting in a single device capable of simultaneously harvesting and storing electrical energy when excited mechanically. Additionally, it is proposed that self-charging structures be embedded into host structures such that they support structural load during operation. An electromechanical assumed modes model used to predict the coupled electrical and mechanical response of a cantilever self-charging structure subjected to harmonic base excitation is described. Experimental evaluation of a prototype self-charging structure is then performed in order to validate the electromechanical model and to confirm the ability of the device to operate in a self-charging manner. Detailed strength testing is also performed on the prototype device in order to assess its strength properties. Static three-point bend testing as well as dynamic harmonic base excitation testing is performed such that the static bending strength and dynamic strength under vibration excitation is assessed. Three-point bend testing is also performed on a variety of common piezoelectric materials and results of the testing provide a basis for the design of self-charging structures for various applications.

Multifunctional vibration energy harvesting in unmanned aerial vehicles (UAVs) is also investigated as a case study in this dissertation. A flight endurance model recently developed in the literature is applied to model the effects of adding piezoelectric energy harvesting to an electric UAV. A remote control foam glider aircraft is chosen as the test platform for this work and the formulation is used to predict the effects of integrating self-charging structures into the wing spar of the aircraft. An electromechanical model based on the assumed modes method is then developed to predict the electrical and mechanical behavior of a UAV wing spar with embedded piezoelectric and thin-film battery layers. Experimental testing is performed on a representative aluminum wing spar with embedded self-charging structures in order to validate the electromechanical model. Finally, fabrication of a realistic fiberglass wing spar with integrated piezoelectric and thin-film battery layers is described. Experimental testing is performed in the laboratory to evaluate the energy harvesting ability of the spar and to confirm its self-charging operation. Flight testing is also performed where the fiberglass spar is used in the remote control aircraft test platform and the energy harvesting performance of the device is measured during flight.
Ph. D.

Energy harvesting technologies have drawn much attention as an alternative power source of roadway accessories in different scales. Piezoelectric energy harvesting consisting of PZT piezoceramic disks sealed in a protective package is developed in this work to harness the deformation energy of pavement induced by traveling vehicles and generate electrical energy. Six energy harvesters are fabricated and installed at the weigh station on I-81 at Troutville, VA to perform on-site evaluation. The electrical performance of the installed harvesters is evaluated by measuring the output voltage and current generated under real traffic. Instant and average power outputs are calculated from the measured waveforms of output voltage and current. The analysis of the testing results shows that the electrical productivity of the energy harvesters are highly relevant to the axle configuration and magnitude of passing vehicles. The energy transmission efficiency of the energy harvester is also assessed.
Ph. D.

Dans le cadre de la récupération d'énergie pour les micro-générateurs (dispositifs sans fil et autoalimentés), ce travail explore les possibilités de récupérer de l'énergie pyroélectrique à l'aide de matériaux ferroélectriques. La source d'énergie est une variation temporelle de température. Dans un premier temps, la récupération d'énergie avec un matériau pyroélectrique linéaire (film PVDF) a été étudiée en utilisant la technique non linéaire du Synchronized Switch Harvesting on Inductor (SSHI). Cette technique a été développée originellement dans le cas de la récupération d'énergie piézoélectrique, et permet un gain considérable de l'efficacité de la récupération. Cette technique a été appliquée au cas pyroélectrique, et comparée avec une technique standard. Le rendement énergétique de ces 2 techniques a été comparé au cycle idéal de Carnot. La technique du SSHI avec des matériaux pyroélectriques est en pratique simple, mais la puissance récupérée et le rendement par rapport à Carnot sont faibles. Afin d'augmenter la conversion d'énergie, il a été étudié l'intérêt des transitions de phase ferroélectriques, au voisinage desquelles l'activité pyroélectrique et électrocalorique est maximale. Dans ce but, les transitions de phase du monocristal relaxeur Pb(Zn1/3Nb2/3)0. 955Ti0. 045O3 ont été utilisées en association avec le cycle thermodynamique d'Ericsson. Le rendement du cycle d'Ericsson utilisant la transition ferroelectrique-ferroelectrique (FE-FE) est beaucoup plus important que pour les techniques utilisant les propriétés linéaires des matériaux pyroélectriques. Il permet en effet d'augmenter d'un facteur 100 le rendement relatif à Carnot par rapport aux essais avec le film de PVDF associé à la technique SSHI. Enfin, pour une variation de température de 10 C, la puissance récupérée avec le cycle d'Ericsson associé à une transition de phase est 3 fois plus élevée que la puissance qu'on peut atteindre avec un dispositif de récupération thermoélectrique
In the framework of energy harvesting for microgenerators (for wireless and self powered electronics), this PhD investigates the capabilities of pyroelectric energy harvesting using ferroelectric materials. The energy source in this work is a time varying temperature. First, the energy harvesting using a linear pyroelectric material (PVDF film) was studied using Synchronized Switch Harvesting on Inductor (SSHI) nonlinear technique. This technique has been firstly developed in case of piezoelectric energy harvesting, and allows a very large effectiveness enhancement. This technique was applied for pyroelectric energy harvesting, and it has been compared with Standard technique. Efficiencies of these techniques were compared with Carnot cycle. The SSHI technique with pyroelectric material is in fact straightforward, but the harvested power and efficiency related to Carnot cycle are small. In order to improve the energy conversion, it was investigated phase transitions at which the pyroelectric and electrocaloric activity are maximum. For this purpose, phase transitions of relaxor Pb(Zn1/3Nb2/3)0. 955Ti0. 045O3 single crystals were used associated with the thermodynamic Ericsson cycle. The efficiency of the Ericsson cycle using the ferroelectric-ferroelectric (FE-FE) transition is much higher than techniques using linear properties of pyroelectric materials (gain of a factor of 100 compared to PVDF associated to SSHI technique). Finally, for a temperature variation of 10°C, harvested power using FE-FE transition and Ericsson cycle could reach 3 times the power that could be obtained using a thermoelectric harvester

Mestrado em Engenharia Eléctrónica e Telecomunicações
Numa época em que os avanços tecnológicos se concretizam a um ritmo frenético, verifica-se uma desproporcional evolução das capacidades das baterias, essencialmente nos equipamentos móveis de uso comum. Por outro lado aumentam os dispositivos cuja localização remota torna a manutenção de baterias algo expensiosa e por vezes insustentável, tais como as Wireless Sensor Networks (WSN) O intuito deste trabalho prende-se não só com o aumento da eficiência de sistemas de recolha de energia de radiação electromagnética da banda dos 100MHz, como também com a introdução de novos métodos úteis à a sua análise. Paralelamente é ainda proposto um sistema de iluminação alimentado por circuitos de rectificação com um enfoque mais específico e menos relacionado com as suas eficiências. Ao nível dos melhores resultados obtidos para os circuitos de alta eficiência, estes foram alcançados por um circuito rectificador série simples, com valores de eficiência experimental de _ 45% para uma potência de entrada de 5dBm, gerando uma tensão de saída de _ 1:6V . Relativamente aos circuitos desenvolvidos para o sistema de iluminação foi possível, através de um multiplicador de tensão, gerar tensões DC ligeiramente acima de 8V para uma potência de entrada de 10dBm, desta forma conseguindo alimentar uma célula de três LEDs de baixo consumo. Os resultados obtidos destinam-se não apenas a apresentar conclusões inovadoras, mas também a fornecer ferramentas adequadas a posteriores desenvolvimentos de sistemas similares, servindo desta forma como um contributo de utilidade para a comunidade científica.
At a time when technological advances happen every day, a disproportional evolution of batteries capabilities has been verified, specially for mobile devices. On the other hand the number of devices whose remote location makes battery maintenance very expensive, Wireless Sensor Networks (WSN), is increasing. The objective of this work is not only to increase the eficiency of energy harvesting systems on the frequency of 100MHz, as it is introducing new methods for it's analysis. At the same time a no-cost illumination system, fed with more specific rectification systems, with less consideration for the eficiency is proposed here. As of the best results obtained for the high eficiency circuits, these were achieved for a simple series rectifier, with eficiencies around 45% for an input power of 5dBm, thus generating output voltages of _ 1:6V . The circuits developed for the lighting system, consisting in voltage multipliers, generated output voltage values around 8V for Pin = 10dBm, that is, enough to power up a low consuming 3 Light-Emitting Diode (LED)s cell. These obtained results are destined not only to present innovative conclusions, but also to provide adequate tools for subsequent developments of similar circuits, thus serving as a contribute for the scientific community.

Conventional thermoelectric materials found in many thermoelectric devices have unfavourable properties; they often suffer instability at high temperatures and contain toxic metals which pose a hazard to the environment. Oxide thermoelectric materials are stable, less toxic and could eventually replace conventional materials. The thermoelectric performance of oxide materials currently do not match conventional materials however, there is potential for improvement through doping and altering the microstructure and chemistry through modification of the processing conditions. This project aims to examine the doping and processing conditions and the effect this has upon the thermoelectric behaviour of oxide based thermoelectric materials. Zinc oxide (ZnO) has been investigated as an oxide thermoelectric material and doping of ZnO with aluminium (Al) and antimony (Sb) by mixed oxide synthesis was investigated. Al2O3 and Sb2O3 were used as aluminium (Al) and antimony (Sb) dopant sources for ZnO, which were reacted with ZnO at temperatures of 1000°C-1300°C. Al was found to incorporate effectively into the ZnO system and was shown to produce n-type behaviour. The Sb doped ZnO material was also found to display n-type behaviour which is intriguing as Sb is considered a p-type dopant in the ZnO system; at low levels <1.0at.%, Sb incorporates onto the Zn site rather than the O site as expected, which leads to n-type behaviour. The addition of Sb dopant leads to the formation of secondary phase of Zn7Sb2O12, which appears to increase the Seebeck coefficient by an energy filtering effect with higher levels of dopant leading to higher levels of secondary phase. Grain size and porosity also play a significant role in both the Al and Sb doped systems with small grains and higher levels of porosity leading to higher values of Seebeck coefficient up to -100µV.K-1 for Al (0.5at.%) and - 115µV.K-1 for Sb (0.8at.%). The ZT figure of merits were found to be highest for materials sintered at 1300°C with values of 6×10-5 and 2×10-10 for Al and Sb doped ZnO respectively, these values are low compared to literature values, which are in the region of 0.01. This is due to high electrical resistivities of the synthesised samples, which is linked to porosity. A better understanding of the effects that microstructure plays on thermoelectric behaviour has been developed and procedures to isolate the contributions from grain size, and degree of dopant incorporation to the thermoelectric properties have been conducted.

The thesis describes various modifications of the predator-prey model. The modifications are considering several harvesting methods. At the beginning a solution and a sensitivity analysis of the basic model are provided. The first modification is the percentage harvesting model, which could be easily converted to the basic model. Secondly a constant harvesting including a linearization is derived. A significant part is devoted to regulation models with special a focus on environmental applications and the stability of the system. Optimization algorithms for one and both species harvesting are derived and back-tested. One species harvesting is based on econometrical tools; the core of two species harvesting is the modified Newton's method. The economic applications of the model in macroeconomics and oligopoly theory are expanded using the methods derived in the thesis.

Recent years have witnessed an enormous interest in developing solar cells by utilising different materials to increase their efficiency. This interest was motivated by the rapid world demand on cheap and clean energy sources, where the main source of world’s power is the fossil fuels. The current photovoltaics technology can not meet the solar power market due to the very low efficiency provided. The philosophy of this thesis is to find an efficient alternative by designing an efficient nanoantenna for receiving the solar radiation and coupling it to an integrated rectifier for AC to DC conversion. This thesis presents the design and optimisation of different types of nanoantennas with a performance comparison to find the optimum solution for this application. The figure of merit in choosing the best design was the captured electric field in the feed gap of the nanoantenna and the area under curve, which is essential in calculating the harvested energy. In addition, this thesis investigates the use of nanoarray instead of single elements. The aims is to increase the captured electric field at the gap of the array where all the elements will contribute in increasing the field in one common gap. Feeding lines will be employed to drive the captured fields from the centre of each single element towards the common gap. Another reason behind using nanoarrays is to reduce the number of rectifiers by using one rectifier per array instead of one rectifier per single element, and hence increase the total efficiency. Futhermore, a simple analysis on dipole nanoantenna using method of moments (MoM) is presented in this thesis. The results obtained from this method is compared with those found from finite element method (FEM) simulations and an acceptable agreement is achieved. To calculate the total conversion efficiency of solar rectennas, it is important to compute the rectification efficiency of the metal/insulator/metal (MIM) diode along with the coupling efficiency between the antenna and the diode. To this end, quantum mechanics was used to calculate the characteristics of the MIM diode. The results show that bowtie nanoantennas are the best candidate for this application in either the single and array form since they have wider bandwidth and larger area under curve. Additionally, the analysis using MoM gives the designer better understanding on how the system works and exhibits lower complexity and reduced computational requirements.

Paper Presented at the Kuwait Symposium on Management and Technology of Water Resources in Arid Zones, Kuwait, October 5-7, 1987.
The use of water harvesting systems in arid lands offers the potential of making lands productive that are now largely unusable due to lack of water for domestic livestock or agricultural use. As long as there is rainfall a water harvesting system can be designed to collect that rainfall and store it until it can be used for beneficial use. The water harvesting system consists of a catchment and a storage facility. If the water is to be used for agriculture it would also include an agricultural area. The agricultural area could be located within the catchment area or in a separate nearby area. Many different treatments have been tested for use in catchment construction. These treatments increase the runoff by decreasing the permeability of the surface and or reducing the time the water stays on the surface or amount of water trapped on the surface. A list of the more promising treatments in order of their increasing cost, are: (1) Shaped compacted-earth; (2) sodium-treated shaped compacted-earth; (3) wax-treated shaped compacted-earth; (4) gravel-covered plastic; (5) fiberglass-asphalt chipcoated; (6) asphalt-plastic-asphalt chipcoated; (7) rubberized-asphalt chipcoated; and (8) reinforced-mortar-covered plastic. The use of compartmented reservoirs make storage of water more efficient. Evaporation and in some cases seepage losses are reduced using the compartmented reservoir by keeping the water concentrated into a volume with as small a surface area as possible. This method of storage when combined with the collection of runoff from a natural surface or with one that is inexpensively treated makes it practical to provide water for supplemental irrigation. This combination is called a water harvesting agrisystem. Concentration of water in a compartmented reservoir can be accomplished in flat terrain using a pump. If the water is being used at a fast enough rate concentration can also be accomplished by selective removal. Alternatively with topography of a sufficient grade, concentration can be accomplished by gravity. Evaporation control on the compartmented reservoir can be improved by placing an evaporation control barrier on the "last" compartment, the one in which water is concentrated and has water in it the longest time. This enhances the value of the evaporation control barrier and increases the dependable water supply. A computer model has been developed to help in the design of the water harvesting systems including agrisystems with compartmented reservoirs. This program fits on portable personal computers and can thus be taken by the designer to a field location to develop an optimum design at a minimum cost. The model can be improved through calibration in a given area as systems are installed and data collected.

52 pp.
In the arid Southwest, rainfall is scarce and evapotranspiration rates are high. Only natives and some desert-adapted plants can live on 10 or 11 inches of annual rainfall. Other plants require some supplemental irrigation and harvesting rainwater can reduce the use of drinking water for landscape irrigation. This publication discusses the water requirements for some plants and the way to collect rainwater. Its topics include: - Water Harvesting System Components - Simple Water Harvesting System Design and Construction - Complex Water Harvesting Systems

56 pp.
Second Edition, October 2004
In the arid Southwest, rainfall is scarce and evapotranspiration rates are high. Only natives and some desert-adapted plants can live on 10 or 11 inches of annual rainfall. Other plants require some supplemental irrigation and harvesting rainwater can reduce the use of drinking water for landscape irrigation. This publication discusses the water requirements for some plants and the way to collect rainwater. Its topics include: - Water Harvesting System Components - Simple Water Harvesting System Design and Construction - Complex Water Harvesting Systems

In 1984 Maricopa County produced more acres of upland cotton with lower yields than it had in 1987 but also started harvest later. Weather and insects reduced yield and early maturity of the crop; rainfall delayed harvest in the October-November period less than it had in 1987.

A pneumatic harvesting method for jojoba seed was investigated. By constructing a stationary experimental unit, the motion of jojoba seeds and stones, which were close in size and weight to seeds, were examined under the effect of positive, negative, and a combination of both pressures. It was determined that there was a reasonable difference in the motion depending upon test conditions and head design. A vacuum head was designed based on the observations and data obtained from the experiments. Using this head it was possible to pick up jojoba seed without picking up stones. A nonstationary unit was constructed to examine the effect of ground speed on picking efficiency. Results showed that a cleaner harvest using a normal ground speed can be obtained with the new head than with conventional equipment. A blowing head was added to windrow seeds and increase the capacity of the machine. It was determined that when the two heads were used together harvesting field capacity increased, however reduced efficiency was found.

The development of a complete thermoelectric generator and its application on a display polarizer film was successfully accomplished in this thesis. A systematic study of the prospective thermoelectric materials, PEDOT:PSS-based and ${ZnON}$, used for the present application is presented. To the best of our knowledge, this is the first exploration of the thermoelectric parameters of ${ZnON}$ reported here. Thin-film deposition of these materials was performed via both solution- and vacuum-based techniques. In addition, certain doping mechanisms were tested in an attempt to further understand the correlation between electrical conductivity and Seebeck coefficient. A maximum power factor of $42{\mu}Wm^{-1}K^{-2}$ was achieved for the PEDOT:PSS-based thin film at room temperature. It was initially doped via 5vol% of DMSO and sequentially treated with ethylene glycol. Specifically, its electrical conductivity displayed a 2-fold increase after EG treatment, reaching a value of about 1632 Scm$^{-1}$. Systematic studies performed on the association between thin-film thickness and its Seebeck coefficient shows a decrease in the latter as the number of multilayers printed increases. Among the different $O_{2}/N_{2}$ ratios that were tested for ${ZnON}$ thin films, a maximum power factor value of 163${\mu}Wm^{-1}K{-2}$ was achieved with the lowest $O_{2}$ flow rate configuration. In contrast to PEDOT:PSS-based thin films, the ${ZnON}$ displayed the opposite effect on the relation of the Seebeck coefficient with respect to thin-film thickness. Furthermore, a heterostructure was also developed by implementing ${ZnO}$ nanowires into the ${ZnON}$ thin film. ${ZnO}$ nanowires have been fabricated through the hydrothermal method on inkjet-printed patterns of zinc acetate dihydrate. It has been demonstrated that with the right inkjet-printing parameters and substrate temperature, ${ZnO}$ nanowires can be effortlessly fabricated in accordance with the desired pattern variations under low temperature and mild conditions. Finally, a complete device of the thermoelectric generator was fabricated using the above materials and a special set-up developed in order to test the device on the polarizer. The power output achieved from a 1-thermoelectric couple under normal backlight illumination and ambient conditions was 23pW. Overall, it is thought that the particular design and proof of concept presented here can be the basis of a prospective energy harvesting scheme via thermoelectrics in future display-based handheld devices.

This thesis will focus on creating electromagnetic vibration generator for a project ESPOSA. This generator will be used in aeronautical application. There it will be powering required electronics. Electronics is thought a part, which will be sensing, writing and sending required data.

The aim of this thesis was to investigate the question of how to harvest RF energy and if we can harvest enough RF energy for it to be useful in an application. It is aimed towards sensor node applications, commonly used in a typical office environment. The WiFi band was chosen since it is omnipresent in the same environment. With the current development within wireless technology and the IoT domain the demand for low power electronic applications has increased and one of the challenges is to find efficient and sustainable ways of powering these types of devices.The best possible theoretical power content was initially calculated followed by measurements in an office. A circuit was designed containing an impedance matching network and rectifier. A measurement application was constructed using a microcontroller. Measurements were made in an office environment and the maximum harvested energy over 24 hours was 350 mJ. The energy was stored in a supercapacitor and is estimated to be enough to power a low energy sensor for about 30 seconds. A large part of the thesis is devoted to impedance matching involving calculating, simulating and experimenting to get a good result.
Med den nuvarande utvecklingen inom trådlös teknik och IoT-domänen har efterfrågan på elektroniska applikationer med låg effekt ökat och en av utmaningarna är att hitta effektiva och hållbara sätt att driva dessa typer av enheter. Syftet med detta projekt var att undersöka frågan hur vi skördar radiovågsenergi och kan vi skörda tillräckligt mycket med energi för att den ska vara användbar i en applikation. I ett typiskt kontor finns fler källor till radiovågor, däribland WiFi som antas ha en hög nyttjandegrad. Projektet valde att inrikta sig på WiFi bandet och undersöka om det går att utvinna tillräckligt med energi där.Projektet strävade efter att leverera en färdig produkt med alla ingående delar, en antenn, en likriktare, en lagringsenhet och ett matchningsnätverk för att anpassa antenn och likriktare till varandra. För att undersöka hur mycket energi som finns att skörda gjordes först beräkningar och sedan mätningar i bland annat ett typiskt kontor. Det konstaterades att det rör sig om väldigt låga nivåer och betonas att de apparater som använder WiFi klarar av att känna av signaler som är långt mycket lägre än de som krävs för att kunna utvinna energi. Detta innebär alltså att apparaterna kan kommunicera felfritt samtidigt som energiinnehållet är så lågt att det inte går att utvinna någon energi.Projektet ägnar stor del åt att optimera den impedansmatchning som måste ske mellan antenn och likriktare för att största möjliga effektutbyte ska kunna ske. Basen är ett kretskort med ett typiskt impedansnätverk och genom beräkningar, simuleringar och experiment tas en prototyp fram. För att kunna analysera resultaten används en mikrokontroller som tar de analoga värdena, omvandlar dem till digitala och skickar dem till en PC för analys.Mätningar gjordes i en kontorsmiljö och den maximala mängden energi som gick att utvinna var 350 mJ på 24 timmar. Energin lagrades i en superkondensator och bedöms vara tillräcklig för att driva en lågenergisensor i ca 30 sekunder.

2 pp.
RainScapes are the ultimate in water efficient landscaping. RainScapes are beautiful landscapes that once established rely entirely on rain and stormwater (gray water too if available)while preserving tap water for indoor and drinking water needs.

Con il termine Energy Harvesting si intende il processo per cui l’energia, proveniente da fonti alternative viene immagazzinata al fine di renderla disponibile a sensori e dispositivi elettronici. In tal senso l'obiettivo è l'autonomia energetica totale o parziale dei degli stessi. Tale processo viene supportato da molteplici tecnologie e le principali, trattate all'interno dell'elaborato, si basano su: RF(radio frequenza), termico, solare, piezoelettrico. Il componente cardine della trattazione è un piccolo ed efficiente device con funzione di accelerometro e giroscopio prodotto dalla ST-Microelectronics denominato LSM6DSL. Esso riveste compiti di fondamentale importanza nell'analisi di sistemi soggetti a forti stress meccanici che ne potrebbero provocare il cedimento strutturale. Una delle caratteristiche principali di questo sensore è la propensione al risparmio energetico infatti esso presenta un assorbimento di corrente esiguo in relazione ai compiti che svolge. Inoltre tale proprietà è sottolineata anche dalla possibilità di utilizzarlo in diversi regimi operativi dunque, a seconda della precisione che si desidera avere e dei dati che il sensore deve fornire, è possibile utilizzare in maniera distinta o congiunta l'accelerometro e il giroscopio. Di grande interesse è l'analisi applicativa antecedente all'installazione dei sistemi di energy harvesting in quanto per un determinato contesto è possibile distinguere tra le varie tecnologie, atte all'accumulo di energia, quella che meglio si adatta alle condizioni presenti in quell'ambito. Da ciò è facile comprendere che ogni metodologia presenta delle proprie caratteristiche intrinseche che ne determina il vantaggio applicativo in taluni casi rispetto che in altri. Negli ultimi anni si sta lavorando molto in questo ambito perché una maggiore indipendenza energetica si traduce in un minor costo di manutenzione e un'aumento più che considerevole dell'applicabilità dei devices.

Las tendencias en la tecnología actual permiten la reducción tanto en tamaño como en potencia consumida de los sistemas digitales complejos. Esta disminución en el tamaño y el consumo da lugar al concepto de dispositivos portátiles que se integren en la vida pertenencias personales y cotidianas como ropa, relojes, gafas, etc. La fuente de alimentación es un factor limitante en la movilidad de los dispositivos portátiles que se ve reducida por la duración de la batería. Además, debido a los costos y difícil accesibilidad, la sustitución o recarga de las baterías a menudo no es viable para los dispositivos portátiles integrados en ropa inteligente. Los dispositivos vestibles están distribuidos en las pertenencias personales y, por tanto, la recolección de energía del usuario es una alternativa para su alimentación. Dispositivos vestibles pueden crear, al igual que los sensores de una red de sensores inalámbricos (WSN), una red de área corporal. El principal objetivo de esta tesis es el estudio de generadores piezoeléctricos, inductivos y termoeléctricos que recolectan energía del cuerpo humano de forma pasiva. El principio físico de un transductor es el mismo independientemente de si la fuente proviene del entorno o del cuerpo humano. Sin embargo, las limitaciones relacionadas con la baja tensión, corriente y niveles de frecuencia conllevan nuevos requerimientos que no están presentes en el caso de la utilización de las fuentes que ofrece el entorno y que suponen el principal desafío de esta tesis. El tipo de energía entrada y transductor a utilizar forman un tándem donde la elección de uno impone el otro. Es importante que las mediciones se realicen diferentes partes del cuerpo humano, mientras se realizan diferentes actividades físicas para localizar las posiciones y las actividades que producen más energía. El acoplamiento mecánico entre transductor y cuerpo humano depende de la ubicación del transductor y la actividad que se realiza. Un diseño específico, teniendo esto en cuenta puede aumentar más de un 200% la eficiencia del transductor como se ha demostrado con láminas piezoeléctricas situadas en plantillas de zapatos. Se han realizado mediciones de aceleraciones en diferentes partes del cuerpo y diferentes actividades para cuantificar la cantidad de energía disponible en actividades cotidianas. Se ha realizado una simulación a nivel de sistema, modelando los elementos de un sistema de energía autoalimentado. El transductor se ha modelado usando las ecuaciones físicas que lo describen con el objetivo de incluir la parte mecánica del sistema. Se han utilizado modelos eléctricos y de comportamiento para el resto de los componentes. De esta manera, el proceso de diseño de la aplicación en su conjunto (incluyendo la carga y un elemento de almacenamiento de energía cuando es necesario) se simplifica a la hora de lograr los requisitos planteados. Obviamente, la carga debe ser un dispositivo de bajo consumo como por ejemplo un transmisor RF. En este caso, es preferible alimentar la carga de forma discontinua, sin una batería, como se deduce de los resultados obtenidos mediante simulación. Sin embargo, la evolución de los transmisores RF de baja potencia puede cambiar esta conclusión en función sobre todo de la evolución del consumo de energía en stand-by y el tiempo de configuración para la operación de transmisión. Se ha deducido a partir del análisis de los generadores inductivos que el análisis en el dominio temporal permite calcular algunas magnitudes que no están disponibles en el dominio frecuencial. Por ejemplo, la potencia máxima se puede calcular en el dominio frecuencial, pero para aplicaciones de recolección de energía es más interesante saber el valor de la energía recuperada durante un cierto tiempo o la potencia media ya que la potencia generada por las actividades humanas pueden ser muy discontinua. Se ha demostrado que los transductores recolectores de energía son capaces de suministrar alimentación a dispositivos electrónicos de baja potencia, como quedó demostrado con un transmisor RF alimentado por una termogenerador que emplea el gradiente de temperatura existente entre el cuerpo humano y el entorno (3-5 K) y que es capaz de realizar medidas y transmitirlas una vez cada segundo
The trends in technology allow the decrease in both size and power consumption of complex digital systems. This decrease in size and power gives rise to the concept of wearable devices which are integrated in everyday personal belongings like clothes, watch, glasses, et cetera. Power supply is a limiting factor in the mobility of the wearable device which gets restricted to the lifetime of the battery. Furthermore, due to the costs and inaccessible locations, the replacement or recharging of batteries is often not feasible for wearable devices integrated in smart clothes. Wearable devices are devices distributed in personal belongings and thus, an alternative for powering them is to harvest energy from the user. Therefore, the energy can be harvested, distributed and supplied over the human body. Wearable devices can create, like the sensors of a Wireless Sensor Network (WSN), a Body Area Network. A study of piezoelectric, inductive and thermoelectric generators that harvest passive human power is the main objective of this thesis. The physical principle of an energy harvesting generator is obviously the same no matter whether it is employed with an environmental or human body source. Nevertheless, the limitations related to low voltage, current and frequency levels obtained from human body sources bring new requirements to the energy harvesting topic that were not present in the case of the environment sources. This analysis is the motivation for this thesis. The type of input energy and transducer form a tandem since the election of one imposes the other. It is important that measurements are done in different parts of the human body while doing different physical activities to locate which positions and activities produce more energy. The mechanical coupling between the transducer and the human body depends on the location of the transducer and the activity that is done. A specific design taking this into account can increase more than a 200% the efficiency of the transducer as has been demonstrated with piezoelectric films located in the insoles of shoes. Acceleration measurements have been performed in different body locations and different physical activities, in order to quantify the amount of available energy associated with usual human movements. A system-level simulation has been implemented modeling the elements of an energy self-powered system. Physical equations have been used for the transducer in order to include the mechanical part of the system and electrical and behavioral models for the rest of the components. In this way, the process of the design of the complete application (including the load and an energy storage element when it is necessary) is simplified to achieve the expected requirements. Obviously, the load must be a low power consumption device as for example a RF transmitter. In this case, it is preferable to operate it in a discontinuous way without a battery as it is deduced from simulation results obtained. However, the evolution in low power transmission modules can change this conclusion depending mostly on the evolution of the power consumption in stand-by mode and the configuration time in transmission operation. It has been deduced from the analysis of inductive generators that time-domain analysis allows to calculate some magnitudes that are not available in frequency domain. For example, the maximum power can be calculated in frequency domain, but for energy harvesting applications it is more interesting to know the value of the recovered energy during a certain time, or the average power since the power generated by human activities can be highly discontinuous. It has been demonstrated that energy harvesting transducers are able to supply power to present-day low power electronic devices as was demonstrated with a RF transmitter powered by a thermogenerator that employs the temperature gradient between human body and the environment (3-5 K) and that it is able to sense and transmit data once every second.

This dissertation explores and analyses factors which could facilitate Knowledge

Harvesting, and also how important it is for the parent companies. Knowledge

Harvesting is one of the knowledge processes within an international joint venture

network that has not received much attention from the academic community. After

relevant review of the literature in the area of international joint ventures and

knowledge management, the authors of the dissertation created a model. The model

consists of five factors: Motive, Absorptive capacity, Knowledge characteristics,

Trust, and Control. Eight hypotheses are formulated in order to test the model. The

empirical study is concentrated on Swedish companies involved in an international

joint venture with a foreign company. A deductive approach is chosen in order to

answer the research questions, and primary data is collected using an online survey.

The results of the questionnaire are analysed in a descriptive manner and several

conclusions are drawn.

In recent years, vibration-based energy harvesting technologies have gained great importance because of reduced power requirement of small electronic components. External power source and maintenance requirement can be minimized by employment of mechanical vibration energy harvesters. Power sources that harvest energy from the environment have the main advantages of high safety, long shell life and low cost compared to chemical batteries. Electromagnetic, electrostatic and piezoelectric transduction mechanisms are the three main energy harvesting methods. In this thesis, it is aimed to apply the piezoelectric elements technology to develop means for energy storage in munitions launch. The practical problems encountered in the design of piezoelectric energy harvesters are investigated. The applicability of energy harvesting to high power needs are studied. The experience compiled in the study is to be exploited in designing piezoelectric energy harvesters for munitions applications. Piezoelectric energy harvesters for harmonic and mechanical shock loading conditions with different types of piezoelectric materials are designed and tested. The test results are compared with both responses from analytical models generated in MATLAB®
and ORCAD PSPICE®
, and finite element method models generated in ATILA®
. Optimum energy storage methods are considered.

Energy harvesting (EH) was born few decades ago and evolved during the years, however only recently has found more applications thanks to the advent of wireless sensor networks and the developments in microchips technology. This thesis investigates energy harvesting potentialities, in particular those related to solar harvesting in indoor applications. Some of the most common challenges are discussed such as: the best maximum power point tracking (MPPT) algorithm for indoor systems; or the effect of partial shading on output performances. Mathematical and analytical models, for solar panels and batteries, are proposed to simulate at first and simple energy harvesting system. Furthermore two solar technologies, the present one (silicon cells) and the future one (dye sensitized cells), are simulated and tested to exploit their potentialities. Finally different commercial solutions are examined and compared to pick the most relevant for this thesis. They are connected to the solar cells and the output characteristics are measured to determine their performances at different illuminances.

Piezoelectric energy harvesting has been around for almost a decade to generate power from the ambient vibrations. Although the generated power is very small, but there are several ways to increase and enhance the generated power. This project presents different methods of optimizing the output power by changing the structural configuration of the energy harvesters, selection of piezoelectric material and circuit interface of these harvesters. To understand the different steps of the enhancement, the process of energy conversion by piezoelectric material has been first looked at. Different groups of piezoelectric material were studied to see what kind of materials have the ability of increasing the generated power. As mechanical configuration of the energy harvesters has a significant effect on the output voltage, their configuration such as Cantilever beam type, Cymbal type and Circular diaphragms has been described and compared. After the power generated in the piezoelectric crystal , the current is sent to through an interface circuit to get rectified and regulated. This circuit can be modified to increase the power as well. There are several types of circuits that can increase the output voltage significantly. Synchronized Switch Harvesting (SSH) techniques, Synchronous Electric Charge Extraction technique and voltage doubler are such examples. These techniques have been also studied and compared. Because of the outgrowing industry of piezoelectric energy harvesting in Medical field, their function and their progress has also been reviewed.