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Sun, Huihui. "Miniature wind energy harvesters." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/416874/.
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Energy harvesting is a very attractive technique for a wide variety of self-powered microsystems such as wireless sensors. Airflow induced oscillations have been used as an attractive technique for energy harvesting because of its potential capacity for generating electrical power. The aero-elastic instability phenomenon such as flutter has been suggested especially for small scale energy harvesters. This paper describes the design, simulation, fabrication, measurement and performance of a miniature wind energy harvester based on a flapping cantilevered beam. The wind generator is based on oscillations of a cantilever that faces the direction of the airflow. The oscillation is amplified by interactions between an aerofoil attached on the cantilever and a bluff body placed in front of the aerofoil. To achieve the optimum design of the harvester, both computational simulations and experiments have been carried out to investigate the structure. Simulation is achieved with ANSYS to optimise the structure and predict the power generation for practical design. Both piezoelectric materials and electromagnetic transducers are used for the generator and tested. Three prototypes with the same volume of 37.5 cm3 are fabricated and tested through two aspects of the performance namely the threshold wind speed for operation and the output power. Wind tunnel test results are presented to determine the optimum structure and to characterize the performance of the harvesters. The piezoelectric generator is fabricated by thick-film screen printing technique. The optimized device finally achieved a working wind speed range from 2 m/s to 8 m/s. The power output was ranging from 0.35 to 3.6 μW and the open-circuit output voltage was from 0.6V to 1.9V. The first electromagnetic harvester had a working wind speed range from 1.35 m/s to 6 m/s with a maximum power output of 29.8 μW and a voltage of 293 mV. While for the second generator, the wind speed for operation is form 1.5 m/s to 6.5 m/s. The output power is ranging from 8.9 μW to 41 μW and the output voltage is up to 171 mV. Results verified the harvester can effectively convert wind energy into large amplitude mechanical vibration without strict frequency matching constraints.
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Simeone, Luigi. "Nonlinear damping in energy harvesters." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/426890/.
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Energy harvesting from ambient vibration has become an attractive topic in the recent years. Initial studies aimed to maximise the performance of small linear device for different excitation scenarios. These devices were assumed to be located in hostile and inaccessible environments and be able to provide energy for low powered sensors. Due to the limited size of the energy harvesters, however, the amount of power produced was small. More recently, many researchers have considered using nonlinear stiffness to improve the performance of these devices. This thesis, however, focuses on the use of nonlinear damping in energy harvesters. Nonlinear damping may be unwanted and introduced as the mechanism of the harvester, but can also be deliberately introduced to improve the dynamic range of the harvester. Typically ambient vibration generates a relative displacement between the suspended mass and the base in an energy harvester, which induces an electromotive force (EMF) in a circuit that is used to harvest electrical energy. It is possible to introduce nonlinear mechanical damping by having a circuit with a nonlinear resistance. Specifically, a load, in which the current is a third-power function of the voltage is compared with an equivalent linear load for three kinds of excitation such as harmonic, random white noise and random bandlimited noise. According to the numerical and analytical results, the cubic load provides more harvested power at resonance at low levels when compared to an equivalent linear load at the same level of excitation. As the frequency bandwidth of a random excitation becomes wider, to the limit of white noise, as the power generated by the cubic converges to the linear case. Electromagnetic transducer energy harvesters usually adopt a conversion mechanism of motion, such as ball screw or rack and pinion, which introduce a source of loss such as friction. Static friction is then added to the model and this is shown to affect the harvested power at low input levels. Another proposed strategy consists of adjusting the electric load according to the input level, which can also enlarge the dynamic range of performance of energy harvested compared to a device with constant load. To demonstrate the effectiveness of the level-dependent load, an energy harvesting device was designed and manufactured, which comprised of an oscillating beam sprung to the base, and attached to a generator. Across the terminals of the generator, an electric resistance is mounted and the voltage measured is used to compute the harvested power. Experiments are conducted by exciting the harvested with a harmonic input at resonance via a shaker. A level-dependent load and a constant load were separately tested; with results that are in good agreement with the simulations, it is shown that by adjusting the load according to the input level, the harvested power is increased compared to a linear constant load.
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Hogue, Daniel B., and Sarah M. Gregory. "MEMS-based waste vibrational energy harvesters." Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/34678.
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Approved for public release; distribution is unlimitedThe piezoelectric effect is a phenomenon where strain on a piezoelectric crystal structure causes potential difference at its ends. By merging piezoelectric materials and microelectromechanical systems (MEMS), mechanical vibration could cause the necessary displacement in MEMS to create a potential difference that could be used to power electronic devices. Developing new sustainable energy sources and using energy more efficiently is at the forefront of several research initiatives and is a clear priority for the Department of the Navys strategic planning. This thesis aims to design a vibrational energy harvesting MEMS device to harness vibrational waste energy with the goal of producing power for naval applications. The development and widespread use of vibrational harvesting MEMS would aid the effort to meet each of these goals in the Department of the Navy. Any shore based, seagoing, or expeditionary mechanical platform could serve as a kinetic energy source for vibration energy harvesting MEMS. This thesis investigates the physics, materials, design, optimization, and microfabrication process in the creation of such a device. Time-dependent finite element models for two designs have been developed, simulating electrical power output. Microfabrication processes for the designs have also been developed.
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Jalali, Nimra. "ZnO nanorods-based piezoelectric energy harvesters." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8948.
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Piezoelectric nanostructures of ZnO were employed for development of vibration energy harvesters. Columnar nanorod structures of ZnO, incorporated into various heterojunction-based device prototypes, were strained to generate voltage signals. The fabricated devices’ prototypes were based on different top electrodes such as: p-n junction-type Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS)/ZnO devices, metal-insulator-semiconductor type Poly(methyl methacrylate) (PMMA)/ZnO devices. Similarly, various bottom electrode materials based prototypes were also assembled: ZnO/indium tin oxide (ITO), ZnO/silver (Ag) and ZnO/zinc (Zn). The overall device design was based on flexible electrodes and substrates, due to which low temperature (below 100 °C) fabrication processes were implemented. Device performance measurement and characterisation techniques were explored and implemented to improve the reliability of results. These techniques included open-circuit voltage and short-circuit current output measurement, resistive load matching and impedance analysis. The analysed performance of energy harvester was assessed in relation to its constituent material properties. The parameters which affect the energy harvester performance were investigated and for this p-n junction-based (PEDOT:PSS/ZnO) devices were used. It was analysed that devices with optimum shunt (Rsh) and series resistance (Rs), which were in the ranges of 0.08 – 0.17 kΩ and 0.5 – 1.65 kΩ respectively, generated the highest peak open-circuit voltage (Voc) and peak power density (PL) of 90 – 225 mV and 36 – 54 μW cm-2. However, the p-n junction-based devices with low shunt resistance (Rsh), ranged between 0.2 – 0.3 kΩ, were considered to be affected with leakage losses, such as short-circuits. Therefore, these devices generated lower Voc and PL in the range of 20 - 60 mV and 2 - 16 μW cm-2. Similarly, the p-n junction-based devices with higher Rs, ranged between 0.3 – 0.6 kΩ, were adversely affected by I2R losses and therefore their generated power density was also dropped to 0.22 - 0.25 μW cm-2. In addition to parasitic resistance losses, the most significant phenomenon investigated in ZnO energy harvesters was, screening of polarisation ii charges in ZnO. The polarisation screening effects were observed to be related to the electrical properties of device components like electrode material type and conductivity of ZnO. Hence, the effect of electrode electrical properties on electric field screening was investigated. In this regard, device electrodes were varied and their effect on energy harvesting efficiency was studied. A comparison based on the performance of bottom electrodes like indium tin oxide (ITO), silver (Ag) and zinc foil on device performance was made. It was observed that due to lower screening effects of ITO, the ITO-based devices generated voltage output which was two orders of magnitude higher than the zinc foil-based devices. Similarly, the screening effects of top electrode materials, like PEDOT:PSS and PMMA, on device output generation were investigated. The PMMA-based devices generated average 135 mV which was higher than average 100 mV generation of PEDOT:PSS-based devices; which indicated that the PMMA-based devices had slower screening rate. On the contrary, the PMMA-based devices’ 7 times higher series resistance than PEDOT:PSS-based devices caused the PL of PMMA-based devices to be 0.4 μW cm-2, which was two orders of magnitude lower than 54 μW cm-2 generated by PEDOT:PSS-based devices. Further to electrode materials study, polarisation screening caused by electrical properties of ZnO was also anaylsed. In this regard, the surface-induced conductivity of ZnO was decreased by using surface coating of copper thiocyanate (CuSCN). The reduction in ZnO conductivity was considered to reduce the screening of polarisation charges. Consequently, the power density of ZnO devices was enhanced from 54 μW cm-2 to 434 μW cm-2.
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Lechuga, Aranda Jesus Javier. "Interfaces In Hydraulic Pressure Energy Harvesters." Licentiate thesis, Mittuniversitetet, Institutionen för elektronikkonstruktion, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-36106.
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The fourth industrial revolution is here and with it a tidal wave of challenges for its prosperous implementation. One of the greatest challenges frustrating the development of the internet of things, and hence the next industrial revolution, is the powering of wireless sensors, as these depend on batteries with a limited lifetime. Recent advances have shown that energy harvesting technologies can be employed to extend the lifetime of batteries and ultimately replace them, thus facilitating the deployment of autonomous self-powered sensors, key components of the internet of things. Energy harvesting is the process of capturing ambient energy and convertingit into electric power. For energy harvesting devices it is crucial that the transduction of energy is as efficient as possible, meaning that the methods for capturing, interfacing and converting the ambient energy should be understood and characterized for every application. This thesis investigates the harvesting of the energy found in pressure fluctuations in hydraulic systems, a widely used power transmission system used in the industry and consumer applications; the focus is on the fluid interface and energy focusing methods. In summary, the contributions in this thesis show that the methods for converting pressure fluctuations in hydraulic systems to electrical power depend on the hydraulic system environment, in essence, the static pressure and the frequency of the pressure fluctuations. The results can serve as a starting point in the research, design, and development of hydraulic pressure energy harvesters.Den fjärde industriella revolutionen är här vilket innebär en rad utmaningar för att dess utveckling ska bli framgångsrik. En av de största utmaningarna som begränsar utvecklingen av sakernas internet för industriella tillämpningar är strömförsörjningen av trådlösa sensorer då dessa är beroende av batterier med begränsad livslängd. Nya framsteg har emellertid gjorts med tekniker för energiskördning som gör att livslängden för batterierna kan förlängas ochi förlängningen helt ersätta batterierna. Det, i sin tur, möjliggör autonoma sensorer som är självförsörjande på energi som är viktiga komponenter i sakernas internet. Energiskördning är den process som omvandlar energi som finns i omgivningen till elektrisk energi. För att kunna få ut så mycket energi som möjligt så är det avgörande att energiskördarna gör energiomvandlingen så effektivt som möjligt. Det gör att inhämtning av omgivande energi samt gränssnitt och energiomvandling måste förstås och karakteriseras för varje tillämpning. Den här avhandlingen undersöker energiskördning för hydrauliskasystem där tryckfluktuationer i dessa system är energikällan. Syftet med den här studien är att ta fram metoder för uppskattning och karakterisering av de nödvändiga gränssnitten för inhämtning, fokusering, och omvandling av fluktuationer i hydraultryck till elektrisk energi. Sammanfattningsvis visar avhandlingen att metoder för att omvandla tryckfluktuationer i hydraulsystem till elektrisk energi beror på den hydrauliska systemmiljön där det statiska trycket och frekvensen av tryckfluktuationerna är de viktigaste parametrarna. Resultaten kan fungera som utgångspunkt för fortsatt forskning och utveckling av energiskördare för hydrauliska system.
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
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Erturk, Alper. "Electromechanical Modeling of Piezoelectric Energy Harvesters." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/29927.
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Vibration-based energy harvesting has been investigated by several researchers over the last decade. The ultimate goal in this research field is to power small electronic components (such as wireless sensors) by using the vibration energy available in their environment. Among the basic transduction mechanisms that can be used for vibration-to-electricity conversion, piezoelectric transduction has received the most attention in the literature. Piezoelectric materials are preferred in energy harvesting due to their large power densities and ease of application. Typically, piezoelectric energy harvesters are cantilevered structures with piezoceramic layers that generate alternating voltage output due to base excitation. This work presents distributed-parameter electromechanical models that can accurately predict the coupled dynamics of piezoelectric energy harvesters. First the issues in the existing models are addressed and the lumped-parameter electromechanical formulation is corrected by introducing a dimensionless correction factor derived from the electromechanically uncoupled distributed-parameter solution. Then the electromechanically coupled closed-form analytical solution is obtained based on the thin-beam theory since piezoelectric energy harvesters are typically thin structures. The multi-mode electromechanical frequency response expressions obtained from the analytical solution are reduced to single-mode expressions for modal vibrations. The analytical solutions for the electromechanically coupled voltage response and vibration response are validated experimentally for various cases. The single-mode analytical equations are then used for deriving closed-form relations for parameter identification and optimization. Asymptotic analyses of the electromechanical frequency response functions are given along with expressions for the short-circuit and the open-circuit resonance frequencies. A simple experimental technique is presented to identify the optimum load resistance using only a single resistor and an open-circuit voltage measurement. A case study is given to compare the power generation performances of commonly used monolithic piezoceramics and novel single crystals with a focus on the effects of plane-stress material constants and mechanical damping. The effects of strain nodes and electrode configuration on piezoelectric energy harvesting are discussed theoretically and demonstrated experimentally. An approximate electromechanical solution using the assumed-modes method is presented and it can be used for modeling of asymmetric and moderately thick energy harvester configurations. Finally, a piezo-magneto-elastic energy harvester is introduced as a non-conventional broadband energy harvester.Ph. D.
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Hehn, Thorsten [Verfasser], and Yiannos [Akademischer Betreuer] Manoli. "A CMOS Integrated Interface Circuit for Piezoelectric Energy Harvesters = Eine CMOS-Integrierte Schnittstellenschaltung für Piezoelektrische Energy Harvester." Freiburg : Universität, 2014. http://d-nb.info/1123479119/34.
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Tran, Thang Quang. "DYNAMIC RESPONSE OF AND POWER HARVESTED BY ROTATING PIEZOELECTRIC VIBRATION ENERGY HARVESTERS THAT EXPERIENCE GYROSCOPIC EFFECTS." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2157.
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This study investigates energy harvesting characteristics from a spinning device that consists of a proof mass that is supported by two orthogonal elastic structures with the piezoelectric material. Deformation in the piezoelectric structures due to vibration of the proof mass generates voltages to power electrical loads. The governing equations for this electromechanically coupled device are derived using Newtonian mechanics and Kirchhoff's voltage law. The case where the device rotates at a constant speed and is subjected to sinusoidal base excitation is examined in detail. The energy harvesting behavior is investigated for devices with identical piezoelectric support structures (called tuned devices). Closed-form expressions are derived for the steady state response and power harvested. For nonzero rotation speeds, these devices have multifrequency dynamic response and power harvested due to the combined vibration and rotation of the host system. The average power harvested for one oscillation cycle is calculated for a wide range of operating conditions to quantify the devices' performance. Resonances do not occur for cases when the base excitation frequency is fixed and the rotation speed varies. For cases of fixed rotation speed and varying base excitation frequency, however, resonances do occur. The number and location of these resonances depend on the electrical circuit resistances and rotation speed. Resonances do not occur at speeds or frequencies predicted by resonance diagrams, which are commonly used in the study of rotating system vibration. These devices have broadband speed energy harvesting ability. They perform equally well at high and low speeds; high speeds are not necessary for their optimal performance. The impact of the chosen damping model on energy harvesting characteristics for tuned devices is investigated. Two common damping models are considered: viscous damping and structural (hysteretic) damping. Closed-form expressions for steady state dynamic response and power harvested are derived for models with viscous and structural damping. The average power harvested using the model with structural damping behaves similarly at high speeds and low speeds, and at high resistances and low resistances. For the viscous damping model, however, the average power harvested is meaningfully different at high speeds compared to low speeds, and at high resistances compared to low resistances. The characteristics of devices with nonidentical piezoelectric support structures (called mistuned devices) are investigated numerically. Similar to spinning tuned devices, mistuned devices have multifrequency dynamic response and power harvested. In contrast to tuned devices, high amplitude average power harvested occurs near speeds and base excitation frequencies predicted by resonance diagram.
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Li, Xuan. "Design and development of hybrid energy harvesters." Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/42507.
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Hybrid energy harvesters (HEHs) targeting multiple energy forms have been drawing increasing interest in recent years. While large scale photovoltaic power plants are capable of providing energy for domestic usage, research has also been focused on kinetic energy harvester with less power output which can be integrated into self-powered electronics such as implantable device, remote wireless sensor, wearables, etc. A number of successful designs of hybrid energy harvesters have been demonstrated which could scavenge solar and kinetic energy simultaneously. However the structures remain complicated; the majority of the designs involve different types of energy harvesters connected in series, which involves complex fabrication processes. Here, a simple structure based on a p-n junction piezoelectric nanogenerator (NG) was designed. The utilization of columnar piezoelectric n-type ZnO nanorods coated with light absorber layer enabled the device to harvest both kinetic and solar energy. This was adapted to either form a N719-based dye-sensitized solar cell (N719-HEH), or a perovskite solar cell (PSC-HEH). To allow high processing temperatures while maintaining mechanical flexibility, Corning© Willow™ (CW) glass substrate was used and compared to the more common ITO/PET. CW showed 56% lower charge transfer resistance and a related 4 times fold increase in power conversion efficiency for N719-HEHs. Oscillation (NG effect) and illumination (PV effect) testing indicated that both N719-HEHS and PSC-HEHs operated as kinetic and solar energy harvesters separately, with the current generated by the photovoltaic orders of magnitude greater than it from mechanical excitation. In addition, under illumination, both N719-HEHs and PSC-HEHs demonstrated further current output enhancement when oscillation was applied. The fact that the current output under NG+PV condition was higher than the summation of current output achieved under NG and PV conditions individually, suggests the piezoelectric potential originated from ZnO affected the charge dynamics within the devices. Thus, HEHs with enhanced output were successfully designed and developed.
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Li, Yuan. "Investigation into new non-linear energy harvesters." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/388049/.
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Energy harvesting from ambient vibration has arose ever-increasing research interests in recent decades. Using non-linear mechanism for vibration energy harvesting has shown considerable effectiveness due to its capability of generating non-linear responses without the requirement of additional external tuning techniques thus it can harvest energy over broader band of frequencies. In this thesis, a non-linear Smooth and Discontinuous (SD) oscillator is investigated as a new type of SD nonlinear energy harvester to explore the potential of energy harvesting and develop an effective energy harvesting system. The findings of this research are examined to enhance the performance of the energy harvesting efficiency. The nonlinear dynamical properties of SD oscillator are firstly studied. The study shows that the oscillation can be local or global depending on the level of input power and geometric parameters, due to the double well potential mechanism. A harmonic external base excitation is then introduced to investigate the dynamic response and power flow behaviour of a single degree-of-freedom (DOF) SD oscillation system. Both analytical and numerical methods are applied. It has been shown that the existence of bifurcation is sensitive to the nonlinearity and excitation level. The single DOF SD energy harvester is developed by attaching electromagnetic induction system to convert kinetic energy into electrical energy. Moreover, power flow variables, especially the consumed energy by electrical resistor, are calculated to examine the effects of damping and electromechanical coupling coefficients. It is seen that the system is sensitive to both the parameters. The response can be chaotic, periodic or quasi-periodic with a small change of these two values. With the full use of analysis results of the studied single DOF SD system, a two-DOF SD oscillation system is then established. The mass and frequency ratios indicate energy exchange between the two masses. An integrated two-DOF SD vibrational energy harvester is then developed, coupling with the electrical energy extraction system. Parameters in the electrical conversion system are also investigated. It is found that the electrical coupling coefficients have significant influence on power transmission from mechanical to electrical system. Numerical simulation is performed to validate the energy generation efficiency by changing significant system parameters. It shows 50 watts of generated power for the SD energy harvester under harmonic excitation. The results demonstrate improved benefits particularly in terms of broadband vibrational energy harvesting, especially in the frequency region below the resonance frequency, under harmonic external base excitation. In addition, random excitations of both Gaussian white noise and random ocean wave, e.g. JONSWAP wave spectrum to the SD system are studied in detail. The investigations on dynamic behaviours and power flow properties indicate the considerable advantages of SD system in terms of broad band vibrational energy harvesting. The research provides a new insight into the SD vibrational energy harvesting method from both harmonic and stochastic ambient vibrations points of view. The new knowledge base through this study and explored advantages of the new type of nonlinear SD energy harvesting from ambient vibrations lays the theoretical foundation for the future design of SD energy harvester for applications in engineering.
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Thorner, Lauriane Daniele Amelie. "Miniaturized energy harvesters in a fluid environment." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12864.
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This thesis investigates electro-mechanical generator systems which harvest energy from an aquatic environment. Such systems are needed to create maintenance-free sensor platforms for use in autonomous wireless sensor networks which have applications in water quality monitoring. Many energy harvesting mechanisms specific to an aquatic environment already exist but the majority of them have been developed for use in renewable energy generation schemes for large-scale electrical power generation. Energy harvesting, however, remains focused on the miniature scale aiming to generate enough power to run a wireless sensor node. This work therefore focuses on the identification, analysis, prototyping and miniaturization issues of existing marine wave-based energy converters. The analysis of different possible energy harvesting mechanisms is performed and their power densities are investigated as a function of their size. In order to be able to maximize the power density of the chosen energy harvester under all operating conditions, expressions have been derived for a generalized load impedance which optimizes the generator damping and resonant frequency, through changes in load resistance and reactance. Within this maximization, an AC/DC H-bridge converter is simulated as an interface between the harvester and its load. This converter is designed to mimic the required generalized load impedance and tune it so that the entire system adapts to the external working frequency. A prototype of the energy harvester was designed and tested. Based on the observation of a natural whistle made of a doubly clamped blade of grass that produces sounds when it is blown on, a MEMS harvester extracting energy from vortex-induced-vibrations was designed. The study of its feasibility as an energy harvester and the determination of its dimensions at a microscopic scale are interesting as it presents a new way of extracting energy using an electromagnetic transduction mechanism and a manufacturing advantage. A prototype of a generator harvesting energy from Vortex-Induced-Vibrations was developed using conventional engineering processes.
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Elliott, Alwyn David Thomas. "Power electronic interfaces for piezoelectric energy harvesters." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/39965.
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Motion-driven energy harvesters can replace batteries in low power wireless sensors, however selection of the optimal type of transducer for a given situation is difficult as the performance of the complete system must be taken into account in the optimisation. In this thesis, a complete piezoelectric energy harvester system model including a piezoelectric transducer, a power conditioning circuit, and a battery, is presented allowing for the first time a complete optimisation of such a system to be performed. Combined with previous work on modelling an electrostatic energy harvesting system, a comparison of the two transduction methods was performed. The results at 100 Hz indicate that for small MEMS devices at low accelerations, electrostatic harvesting systems outperform piezoelectric but the opposite is true as the size and acceleration increases. Thus the transducer type which achieves the best power density in an energy harvesting system for a given size, acceleration and operating frequency can be chosen. For resonant vibrational energy harvesting, piezoelectric transducers have received a lot of attention due to their MEMS manufacturing compatibility with research focused on the transduction method but less attention has been paid to the output power electronics. Detailed design considerations for a piezoelectric harvester interface circuit, known as single-supply pre-biasing (SSPB), are developed which experimentally demonstrate the circuit outperforming the next best known interface's theoretical limit. A new mode of operation for the SSPB circuit is developed which improves the power generation performance when the piezoelectric material properties have degraded. A solution for tracking the maximum power point as the excitation changes is also presented.
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Khan, Syed Farid Ullah. "Vibration-based electromagnetic energy harvesters for MEMS applications." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/33833.
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This thesis investigates vibration-based electromagnetic energy harvesters (EMEHs) for application in low power autonomous sensors. It makes contributions pertaining to the development of a low cost fabrication technology, analytical modeling, simulations and characterization of EMEHs under harmonic and random vibrations.
A novel, low cost, one mask fabrication technology devised in this thesis is used to develop a copper foil-type linear EMEH, and a polydimethylsiloxane (PDMS) membrane type nonlinear EMEH. The voltage and power generated by these harvesters are comparable to existing EMEHs which use more involved fabrication processes. In the membrane type EMEH the inclusion of a more flexible PDMS membrane design reduces the harvester resonant frequency and makes it suitable for extracting energy from low level vibration environments. For acceleration levels greater than 0.1 g, this harvester exhibits a nonlinear behaviour. At higher levels of narrow band random excitations, the device therefore exhibits broadening of the load voltage spectrum in comparison to the response under relatively low levels of narrow band random excitations.
Analytical models for linear EMEHs with non-uniform magnetic field for harmonic vibrations are developed. A simple analytical model based on Faraday’s law and uniform gradient of the normal component of the magnetic flux density is developed for EMEHs where the entire coil experiences approximately the same gradient of the normal component of the magnetic flux density. However, for EMEHs where the entire coil is not exposed to the same magnetic flux gradient a more robust model, based on the off-center analytical solution of the magnetic flux density is devised. The simulation results of the developed models are in good agreement with the experimental observations.
Analytical models for linear and nonlinear EMEHs under random vibrations are derived. The models are parameterized such that they are applicable to all architectures of EMEHs and can be utilized for designing and performance estimation of EMEHs. Nonlinear harvesters with spring nonlinearity and with combined spring and damping nonlinearity are modeled using the statistical linearization method. The developed models are useful in investigating the effects of the mechanical nonlinearity on the performance and bandwidth of the harvesters under random vibrations.
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Mak, Kuok Hang. "Vibration modelling and analysis of piezoelectric energy harvesters." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12534/.
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The performance of piezoelectric cantilever beam energy harvesters subjected to base excitation is considered in this work. Based on the linear assumption, a theoretical model is developed to predict the mechanical and electrical responses of the harvester and in comparison to other theoretical models, more accurate mode shape functions are used for the structural part of the harvester. The model is validated against experimental measurements and parameter studies are carried out to investigate the maximum power output in different situations. In some applications, like powering tyre pressure monitoring sensors (TPMS), energy harvesters are subjected to large amplitude shocks and high levels of acceleration, which can cause large bending stresses to develop in the beam, leading to mechanical failure. In this work, a bump stop is introduced in the energy harvester design to limit the amplitude of vibration and prevent large amplitude displacement. A theoretical model is developed to simulate the energy harvester impacting a stop, and the model is used to investigate how the electrical output of the harvester is affected by the stop. The work demonstrates how the model can be used as a design tool for analysing the compromise between the electrical output and structural integrity. Nonlinear behaviour of the energy harvester is observed to have a significant effect on the resonance frequencies when the harvester is subjected to large amplitude base accelerations. To correctly predict the behaviour of the harvester, piezoelectric material nonlinearity and geometric nonlinearity are incorporated in the theoretical model. It is found that the nonlinear softening effect is dominated by the material nonlinearity, while the geometric nonlinearity is less significant. The nonlinear energy harvester model is used in conjunction with the bump stop and results obtained using the linear and nonlinear models are compared to experimental measurements to investigate the importance of using a nonlinear model. The inclusion of nonlinear behaviour is shown to improve significantly the accuracy of predictions under some circumstances. The energy harvester models developed in this work are used to simulate the electrical power generated in a TPMS application, where the harvester embedded in the tyre is subjected to large radial accelerations as the tyre rolls along the road. The simulated results are compared to reported experimental work and agreement is found between the results.
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Pedrosa, Steven Michael. "Study of high efficiency micro thermoelectric energy harvesters." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4820.
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Thermal energy sources, including waste heat and thermal radiation from the sun, are important renewable energy resources. Thermal energy can be converted into electricity by thermoelectric phenomena; the thermoelectric phenomena can also be operated in reverse when provided an electric current, producing a temperature gradient across the device. Thermoelectric devices are scalable, renewable, and cost effective products that offer capabilities to harness waste heat or environmental heat sources, and convert the captured heat into usable electricity. The operating principle of a thermoelectric device requires that a temperature gradient be present across the device, which induces the flow of electrons from the hot side of the device to the cold side. Thermoelectric devices are currently hampered by the low conversion efficiencies and strict operating temperatures for certain materials. This study investigates the main factors affecting efficiencies of thermoelectric devices as energy harvesters and aims to optimize the devices for maximum efficiency and lower costs by using microfabrication processes and self-assembled materials for complete thermoelectric modules (TEMs). By first establishing operating conditions and a desired mode of operation, optimization equations have been established to determine device dimensions and performance parameters. Compact integration realized by microfabrication technologies that allow for multiple output voltages from a single chip was also investigated. Additionally, cost savings were found by reducing the number of fabrication processing steps and eliminating the need for precious metals during fabrication. The optimized design proposed in this study utilizes copper electrodes and requires fewer applications of photoresist than previous proposed designs. In fabrication of thin film based micro devices, the film quality and the composition of the film are essential elements for producing TEMs with desired efficiencies. Although Bi2Te3 has been investigated as thermoelectric material, this study determined that there was a possibility that both N-type and P-Type Bi2Te3 could be created from a single electrolyte solution by controlling the amount of Te present in the film. Films were produced with both AC and DC signals and varied composition of Te at.% of Bi2Te3 was achieved by controlling the average current density during electrochemical deposition. A linear relationship was established between the average current density and the resultant Te content. SEM and EDS were used to characterize the morphology and the composition of the thin films created. With the fabricated thermoelectric materials, analytical models could be developed using known material properties of thermoelectric films with a given Te content. The analytical results obtained by the developed optimization equations were comparable with the FEA models produced by using COMSOL, a multiphysics program with powerful solving algorithms that was used to evaluate designs. Further improvements to device performance can be achieved by designing a segmented thermoelectric device with multiple layers of thermoelectric material to allow the device to operate across a larger temperature gradient.ID: 031001306; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed March 18, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 88-89).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Miniature Engineering Systems Track
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Householder, Timothy J. "MEMS-based waste vibration and acoustic energy harvesters." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/44583.
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Approved for public release; distribution is unlimitedEvery machine vibrates and emits noise. This is unused energy that, with an appropriate mechanism, can be returned to the system. Utilizing an array of piezoelectric microelectromechanical systems (MEMS) devices to harvest this otherwise wasted energy, it is possible to improve the efficiency of any number of mechanical devices. Piezoelectricity is the mechanism by which certain crystalline structures generate electric potential when under strain, or, conversely, deform when subjected to an electric potential. It is this first effect that is important to this application. Though each MEMS device will generate a very small amount of power, a 1 m2 area can contain an array of millions of these devices. Energy harvesting, conservation, and efficiency are all key Department of Defense (DOD) priorities, and the universal application of these devices make them ideal for any expeditionary platform, such as ships, aircraft, and automobiles. This thesis designs and tests the first generations of acoustic and vibrational piezoelectric MEMS devices; including time-dependent finite element models, microfabrication processes, and the initial attempts at characterization and optimization.
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Cox, Graeme J. "A yield mapping system for sugar cane chopper harvesters." University of Southern Queensland, Faculty of Engineering and Surveying, 2002. http://eprints.usq.edu.au/archive/00004617/.
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[Abstract]: Yield maps provide essential information for the spatial analysis and evaluation of crop production management at a within field level. Technology has been developed to conduct yield mapping in various crops including grain, potatoes and forage, but as yet no technology exists for yield mapping sugar cane. The chopper harvester is the most common form ofmechanical harvester for sugar cane. Therefore, the goal of this research is to develop a yield mapping system for the chopper type sugar cane harvester.After a review, it is proposed that a suitable accuracy goal for the sugar cane mass flow sensor would be ‘less than 5% cumulative measurement error, 95% of the time (2 standard deviations), measured over a 100m2 harvest area’.Existing mass flow sensors for other crops are reviewed.Based on this review four potential techniques are proposed to measure the mass flow rate of sugar cane. These were defined as the chopper power, elevator power and feed roller separation and weigh pad. These weretested simultaneously by placing various sensors on a single harvester and comparing the sensor outputs with the mass flow rate as measured by a weigh truck. In this trial, all techniques offered potential but none produced results close to the accuracy goal. A weighing technique, known as the ‘weigh pad’, offered the most potential for improvement and potential to accurately measure the mass flow rate with a single calibration under all conditions. The weigh pad technique suffered from very small load cell sensitivity to flow rate, drift in baseline readings and susceptibility to mechanical noise/acceleration dynamics.An opportunity arose to install a complete yield mapping system on a harvester within a commercial operation. This opportunity was accepted to assess the potential for applying yield maps to the agronomic management of sugar cane. Because the weigh pad sensor required further development at this stage, chopper and elevator power were used as a measure of mass flow rate. A full yield mapping system was developed. Yield mapping, directed soil sampling and variable rate gypsum application was conducted on a case study field. Economic analysis shows a clear economic benefit when compared with standardmanagement.Analysis is conducted on the weigh pad sensor examining its susceptibility to mechanical noise/acceleration dynamics. Theory is developed to mathematically model the effects of acceleration dynamics on the accuracy of weigh pad sensor. Laboratory bench testing supported the mathematical model. From the theoretical and experimental analysis a number of conclusions are drawn:· The weigh pad should be made as light as possible to minimise the error due todynamic conditions.· Electronic analogue filters should be used to reduce the noise due to externalacceleration.· The weigh pad should be as rigid as possible to maximise its natural frequency.A new weigh pad sensor was designed based on these conclusions. Field trials indicated the effects of external accelerations dynamics were significantly reduced. Baseline drift was then found as the next major factor limiting accuracy. The baseline drift was principally caused by the secondary extractor fan of the harvester inducing a negative pressure on the weighpad. A rubber curtain placed between the weigh pad and the secondary extractor fan reduced the negative force on the weigh pad due to the secondary extractor fan by 74% (from 17 N to 4.4 N). Therefore it is recommended the curtain be used to minimise the impact of the secondary extractor fan on the baseline drift of the weigh pad.A yield mapping system has been developed for the sugar cane chopper harvester incorporating the weigh pad sensor, a ground speed sensor, a DGPS receiver, a yielddisplay/monitor and data logger. Three identical systems have been constructed and installed on three harvesters for the 1998 cane harvest season. The results show sugar cane could be yield mapped using standard yield mapping principles.The level of accuracy being achieved by the yield mapping system is less than 16% error, with 95% confidence, over a measurement area of approximately 1400 m2. Although theaccuracy achieved is not to the desired research goal, yield maps were produced with satisfactory detail to make agronomic management decisions. The reliability of the sugar cane yield mapping system under field condition in a commercial operation was satisfactory. However, two techniques are proposed (“auto-zeroing” and “batch weighing” techniques) to improve the accuracy and reliability of the weigh pad readings during wet or adverseharvesting conditions.After note: At the time of writing the NCEA along with Case Austoft (CNH) were continuing to conduct research and development on the system and are intending to make theyield mapping system available as a standard item on new harvesters and a retrofit unit on existing harvesters in the near future (C. Barret, per. comm. 2001). The proposed “autozeroing” and “batch weighing” techniques are being tested.
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McCarthy, Stuart George. "The integration of sensory control for sugar cane harvesters." University of Southern Queensland, Faculty of Engineering and Surveying, 2003. http://eprints.usq.edu.au/archive/00001469/.
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The research concerns the design and implementation of mechatronic systems to assist in the operation and control of a sugar cane harvester. Two functions were chosen for attention, the primary separation system, and the ‘topper’ that discards the leafy crown. Although these operations are given low priority by the operator of the harvester, their optimisation is of particular significance to the industry. Optimum separation requires a fine balance between discarding ‘trash’ that would contaminate the quality of the cane billets and losing good sugar-bearing material through over cleaning. Poor control of the topper can create extra load for the separation system and cause it to operate at a low efficiency with high loss. Alternatively it can cause a length of sugar-bearing cane stalk to be lost before it even enters the harvester system at all. A variety of mechatronic techniques were explored, that addressed the problem of providing useful data directly from the harvester functions and the electronic instrumentation to allow the data to be collected in a useful form in real-time. Computer control issues were also investigated, to make best use of the data stream. Novel acoustic transducers were introduced to the sensory separation system to provide a signal that indicated material striking the fan blades. A rotary transformer was required to allow transmission of the signal, and a signal interface system was implemented to record the returned data. Many real-time time-series analyses were conducted, and from these a suitable algorithm to extract an impact signal was developed. This system was assessed under harvesting conditions with results that confirmed its ability to quantify the amount of cane lost from the harvest. An investigation was conducted to detect the optimum topping height on a sugar cane stalk. The techniques considered both the internal and external attributes of the stalk, and a method was selected to measure the sugar concentration with a chemical sensor. An important design parameter was that the sensor must operate on the harvester in real time. The novel refractometer worked well in laboratory conditions, yielding repeatable and accurate results. The field environment complicated the application of this system, however this was partly overcome with introduction of a custom sample-crushing mechanism. This device provided the necessary juice sample from a selection of the topped cane stalks. The complete sampling and measuring mechanism operated well on cane stalks, and returned encouraging results. Both sets of data returned useful information regarding the operation of the particular harvester operations. The control of either the separation system or the topper requires careful balancing, and novel control techniques that consider the ergonomics for the operator are discussed. These include visual indication devices through to automatic control algorithms. With the integration of mechatronic techniques into the functioning of the sugar cane harvester, the overall efficiency of many of its functions may be improved, and the operator’s task may be greatly simplified. The ultimate objective is to maximise the yield with an improved level of harvested and separated cane.
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Frazier, Kyle W. "Safety and health perceptions and concerns of custom harvesters /." Available to subscribers only, 2006. http://proquest.umi.com/pqdweb?did=1136090901&sid=18&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Patel, Rupesh. "Modelling analysis and optimisation of cantilever piezoelectric energy harvesters." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13246/.
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Over the last decade there has been a growing increase in research in the field of vibrational energy harvesting - devices which convert ambient vibrational energy into electrical energy. The major application area for such devices is as power sources for wireless sensors, thereby replacing currently used batteries which suffer from a finite lifespan and pose environmental issues during disposal. The vast majority of designs are cantilever beams comprising of piezoelectric layers having coverage identical to the substrate layer. It is evident from the literature that rudimentary work has been performed on design optimisation, with reliable and extensive parametric studies on geometry, especially piezoelectric layer coverage, being overlooked. As a result of this, outcomes from previous research are yet to be seen in designs for practical applications. In this work a versatile linear model is developed which can accurately predict the performance of cantilever piezoelectric energy harvesters. An integral part of the model uses a transfer matrix method to accommodate the difference in structural dynamics of both uniform and non-uniform structures with model validation provided through extensive experimental work. The linear model developed is used to carry out parametric studies on the geometry of three distinct energy harvester cases thereby providing comprehensive knowledge on key variables and geometrical changes which can improve performance. In one of the cases examined, an improvement in performance of over 100% is predicted by solely altering piezoelectric layer coverage. However, the load resistance, i.e. electrical condition, has a significant effect on the trends in generated power which led to work directed toward harvester optimisation in a more realistic electrical scenario. Investigation on harvester geometry whilst utilising an electrical scenario comprising of an energy storage medium is undertaken in this work. The developed model ensures the effects of electro-mechanical coupling remain and provides a solid basis from which users can readily apply model extensions through inclusion of further electrical components to resemble practical circuitry. Theoretically, for all examined case studies, improvements in performance were realised through alterations to piezoelectric layer dimensions with the most notable result indicating an improvement of over 200% during optimisation of piezoelectric layer length. In conjunction to theoretical findings, outcomes of extensive experimental work are provided in order to highlight the accuracy and reliability of the presented theoretical models in both electrical scenarios. Variation in mechanical damping magnitude plays a pivotal role throughout experimental testing and is one key factor in explaining why devices comprising of shorter piezoelectric layers have high performance. A methodology behind unbiased design comparisons is also provided in this work, and involves comparing devices with identical fundamental frequencies. The reasoning behind this approach is to allow for each device to perform as efficiently as possible in the same excitation scenario. Systematic alterations to multiple geometric parameters are used to achieve this. Geometric parameters such as the substrate thickness are observed to provide adequate frequency control. Using this approach, performance improvements from adjustments to piezoelectric coverage still remain. The occurrence of non-linearity in piezoelectric materials is a widely known phenomena and so lastly, a more robust model is provided which incorporates material and geometric non-linearity. This model is useful in determining dynamical responses of uniform and non-uniform piezoelectric energy harvesters when subjected to moderate-to-high acceleration levels. A thorough validation of the theoretical model is achieved using extensive experimental data obtained from a range of samples. For the harvester composition tested in this work, the occurrence of mild non-linearity at base acceleration levels as low as 1 meter per second squared is witnessed with softening behaviour causing the resonant frequency to decrease with base acceleration. In order to avoid reduced efficiency in the final application, the prediction of possible frequency shifts is vital during the design process.
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Kluger, Jocelyn Maxine. "Nonlinear beam-based vibration energy harvesters and load cells." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87958.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 216-218).
This thesis studies a novel nonlinear spring mechanism that is comprised of a cantilever wrapping around a curved surface as it deflects. Static force versus displacement tests and dynamic "initial displacement" tests verified the spring theory for a large range of oscillator parameters. Various human motion energy harvester configurations that use the nonlinear spring were numerically optimized for power, robustness, and adaptivity. Based on the optimization results, both the nonlinear and linear devices studied in this thesis generate more power per volume and per mass when excited at one's hip while walking than current commercial energy harvesters. The two degree-of-freedom (2DOF) nonlinear oscillator is more adaptive to different excitation signals and resistant to power decay when parasitic damping is present than the IDOF and 2DOF linear systems. These significant advantages are caused by the 2DOF nonlinear system harvesting its optimal power at large electromagnetic damping coefficients, whereas the optimal power generation for the linear systems occurs at low electromagnetic damping coefficients. This thesis also examined what electromagnetic damping coefficients can be generated by magnet-and-coil geometries that satisfy the energy harvester constraints. The final chapter of this thesis investigates a load cell that uses the stiffening spring to maintain high resolution over a large range of forces and prevent large forces from damaging the load cell. Future work will include testing a full energy harvester prototype and exploring other applications of the nonlinear spring.
by Jocelyn Maxine Kluger.
S.M.
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Yoon, You C. (You Chang). "Design of test bench apparatus for piezoelectric energy harvesters." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/86267.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, June 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (page 48).
This thesis presents the design and analysis of an experimental test bench for the characterization of piezoelectric microelectromechanical system (MEMS) energy harvester being developed by the Micro & Nano Systems Laboratory research group at MIT. Piezoelectric MEMS energy harvesters are micro-devices that are able to harvest energy from their ambient vibrations using piezoelectric material property, and many different designs are being researched by the Micro & Nano Systems Laboratory. In order to analyze the different designs, it is crucial to have a flexible test bench, and the test bench created in this thesis allows data to be gathered easily from different energy harvesters. After the test bench is designed and created, it is used to excite a linear cantilever beam energy harvester system at different frequencies and values for open circuit voltage, resonance frequency, and maximum power are calculated from the collected experimental data. In addition, theory behind linear and nonlinear energy harvester systems is investigated and important definitions, characteristics, and equations are summarized in this thesis.
by You C. Yoon.
S.B.
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Joo, Han Kyul. "Single-degree-of-freedom energy harvesters by stochastic excitation." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92138.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 97-100).
In this thesis, the performance criteria for the objective comparison of different classes of single-degree-of-freedom oscillators under stochastic excitation are developed. For each family of oscillators, these objective criteria take into account the maximum possible energy harvested for a given response level, which is a quantity that is directly connected to the size of the harvesting configuration. We prove that the derived criteria are invariant with respect to magnitude or temporal rescaling of the input spectrum and they depend only on the relative distribution of energy across different harmonics of the excitation. We then compare three different classes of linear and nonlinear oscillators and using stochastic analysis tools we illustrate that in all cases of excitation spectra (monochromatic, broadband, white-noise) the optimal performance of all designs cannot exceed the performance of the linear design. Subsequently, we study the robustness of this optimal performance to small perturbations of the input spectrum and illustrate the advantages of nonlinear designs relative to linear ones.
by Han Kyul Joo.
S.M.
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Good, Grant. "Feasibility of diesel-electric hybrid drives for combine harvesters." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/19754.
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Master of AgribusinessDepartment of Agricultural Economics
Jason Bergtold
Efficiency and technology are increasingly important selling points for combine harvesters. Diesel-electric hybrid drives have taken hold in the construction equipment industry, and are providing marketable efficiency benefits for some heavy equipment customers. This thesis explores the technical and economic feasibility of utilizing diesel-electric hybrid drives on AGCO combine harvesters. To determine the technical feasibility of utilizing diesel-electric hybrid drives on AGCO combine harvesters, a search was conducted for prior literature relating to the use of electric drives on other heavy, off-highway equipment. This information, coupled with data provided by experts in the field, was used to determine if electric drives could fulfill the unique requirements of combine harvesters, and be practically utilized for this application. To determine the economic feasibility of utilizing diesel-electric hybrid drives on AGCO combine harvesters, an optimization model was constructed to seek out the most economically viable configuration of electric drives for this application. The model takes in to consideration the different use-cases in which this equipment is expected to perform, as well as the component costs and operating efficiencies of both the drives in place currently and the proposed electric drives. The outcome of the model was then utilized to compare the best-case configuration to the minimum requirement for economic feasibility. The technical feasibility assessment conducted for this thesis led to the conclusion that it would be technically feasible to utilize electric drives on a combine harvester. There are commercially available electric drive components which are suitable for use in the environment that this equipment is expected to operate in, and a prototype combine harvester having electric drives has previously been constructed. The economic feasibility assessment conducted for this thesis revealed that it is not economically feasible to utilize electric drives on AGCO combine harvesters at this time. Under the current circumstances, the most economically viable configuration would take nearly twice the machine’s usable operating life to provide a benefit to a customer from fuel savings. Sensitivity analysis revealed that significant changes in the price of fuel or electric drive components would be necessary to change the outcome of this study.
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Crowe, Jennifer. "Heat exposure and health outcomes in Costa Rican sugarcane harvesters." Doctoral thesis, Umeå universitet, Epidemiologi och global hälsa, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-93609.
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Background The remarkably efficient mechanisms of the human body to maintain its core temperature of 37°C can be inadequate when harsh climatic conditions and excessive muscle movement lead to heat stress, dehydration and potential heat illness, ranging from minor symptoms such as fatigue to a potentially fatal heat stroke. Agricultural workers in the tropics are at high risk, which is expected to increase with climate change. Sugarcane harvesting in Costa Rica is largely done by cutting the cane with a machete, by temporary, sub-contracted workers who are often migrants and living in poverty. Sugarcane harvesters are known to be affected by an epidemic of chronic kidney disease of non-traditional origin, currently hypothesized to be related to working conditions. Objectives This work aimed to better understand and document sugarcane harvester exposure to heat and the health consequences of working under such conditions. Specific objectives were to 1) Document working conditions and heat in the Costa Rican sugarcane industry (Paper I); 2) Quantify heat stress exposures faced by sugarcane harvesters in Costa Rica (Paper II); and 3) Quantify the occurrence of heat stress symptoms and abnormal urinary parameters in sugarcane workers in Costa Rica (Papers III and IV). Methods This study took place over three harvests following a pilot assessment prior to the first harvest. Methods included direct observation, semi-structured interviews with 24 individuals and a participatory workshop with 8 harvesters about heat-related perceptions, exposures and coping strategies during the harvest and non-harvest season (Pilot). Researchers accompanied workers in the field during all three harvests, measured wet bulb globe temperature (WBGT) and conducted direct observation. Heat exposure assessment was conducted by calculating metabolic load, WBGT and corresponding limit values based on international guidelines (NTP and OSHA) (Harvest 1). Self-reported symptom data were collected using orally-administered questionnaires from 106 sugarcane harvesters and 63 non-harvesters from the same company (Harvest 2). Chi-square test and gamma statistic were used to evaluate differences in self-reported symptoms and trends over heat exposure categories. Finally, liquid consumption during the work shift was documented and urinalysis was conducted pre-and post-shift in 48 sugarcane harvesters on three days; differences were assessed with McNemar´s test on paired proportions (Harvest 3). Results Sugarcane workers in both the harvest and non-harvest seasons are exposed to heat, but particularly during the harvest season. Field workers have to carry their own water to the field and often have no access to shade. Some plantworkers are also exposed to intense heat. The metabolic load of sugarcane harvesting was determined to be 261 W/m2. The corresponding threshold value is 26 ◦C WBGT, above which workers should decrease work load or take breaks to avoid the risk of heat stress. Harvesters in this study were at risk of heat stress as early as 7:15 am on some mornings and by 9:00 am on all mornings. After 9:15 am, OSHA recommendations would require that harvesters only work at full effort 25% of each hour to avoid heat stress. Heat and dehydration symptoms at least once per week were experienced significantly more frequently among harvesters than non-harvesters (p<0.05): headache, tachycardia, fever, nausea, difficulty breathing, dizziness, and dysuria. Percentages of workers reporting heat and dehydration-related symptoms increased over increasing heat exposure categories. Total liquid consumed ranged from 1 to 9 L and differed over days (median 5.0, 4.0 and 3.25 on days 1, 2 and 3 respectively). On these same days, the two principle indicators of dehydration: high USG (≥1.025) and low pH (≤5), changed significantly from pre to post-shift (p=0.000 and p=0.012).Proportions of workers with proteinuria >30 mg/dL, and blood, leucocytes and casts in urine were also significantly different between pre and post-shift samples at the group level, but unlike USG and pH, these alterations were more frequent in the pre-shift sample. 85% of workers presented with proteinuria at least once and 52% had at least one post-shift USG indicative of dehydration. Conclusion Heat exposure is an important occupational health risk for sugarcane workers according to international standards. A large percentage of harvesters experience symptoms consistent with heat exhaustion throughout the harvest season. Pre and post-shift urine samples demonstrate dehydration and other abnormal findings. The results of this study demonstrate an urgent need to improve working conditions for sugarcane harvesters both under current conditions and in adaptation plans for future climate change.
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Larson, Geremy. "Self-propelled forage harvester sales analysis." Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/35746.
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Master of AgribusinessDepartment of Agricultural Economics
Major Professor Not Listed
Self-propelled forage harvesters are used to make feed for livestock. Producers prefer forage made with these machines because they are able to deliver a feed value that enables improved productivity of their animals in terms of milk production for dairy animals and weight gain for beef animals. Self-propelled forage harvesters are able to make a variety of feed from different crops, including whole-plant corn silage, earlage, and haylage, among others. The self-propelled forage harvester is a complex and expensive piece of machinery for a producer to own. The self-propelled forage harvester market in the United States is a growing market, but small when compared to other equipment such as combines. In today’s environment, productivity is crucial to the success of the agricultural producer. Self-propelled forage harvesters are no exception. Growth of the self-propelled forage harvester market is reflected in increased unit sales, total horsepower sold, and average horsepower of the selfpropelled forage harvesters sold in the United States. This study looks at changes in the number and size of self-propelled forage harvesters being purchased and what factors might be driving those changes. This study found that the amount of milk produced, the type of customer purchasing the equipment, and the average price of milk a producer received explained 81.2% of the variation in the number of self-propelled forage harvesters sold from 2000- 2014. Study results also show that the size of dairy operation, the type of customer purchasing the equipment, and the average price of milk explained 88% of the variability in total horsepower of self-propelled forage harvesters sold from 2000-2014. Finally, the size of dairy operation that a typical cow comes from, the type of customer purchasing the equipment, and the average price of corn were able to explain 98% of the variation of average horsepower of self-propelled forage harvesters over that same time period. The model and analysis will be shared with product planners from John Deere as they develop new machine specifications for self-propelled forage harvesters in the future.
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Goldenetz, Jolie A. "Learning from Traditional Water Harvesters in the Negev and Sonoran Deserts." Arizona-Nevada Academy of Science, 2006. http://hdl.handle.net/10150/296663.
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Bowden, James Anthony. "Electrical tuning of electromagnetic energy harvesters with switched mode power electronics." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616884.
Full textAbstract:
Energy Harvesting is a key enabling technology for highly distributed electronic systems such as wireless sensor networks, One of the most commonly described harvesting techniques is vibration harvesting, where a base-excited resonant mass/spring system is damped via an electromechanical transducer. A significant drawback of the resonant mechanical system, required to amplify low-level base vibrations, is the narrow bandwidth over which the system can operate, This thesis describes work carried out towards a method of increasing the bandwidth of resonant vibration harvesters by synthesising a variable complex load impedance using highly efficient switched-mode converters: loading the harvester with an optimum complex impedance effectively tunes the complete electromechanical system to the excitation frequency. This tuning effect is described analytically and demonstrated in practice with linear impedance emulating circuits. To benchmark the electrically tuned system against a more conventional converter, a micro power resistance emulator was developed, featuring an average quiescent power consumption of 56.6uW and a peak efficiency of 85.4%. The prototype harvester for which this tuning system was developed generates approximately 20mW, presenting a challenge for • converter design. This is further exacerbated when synthesizing large reactive loads at tuning frequencies far from mechanical resonance where the apparent power is much larger than the real power delivered from the harvester. To achieve the desired performance a custom micropower VSC power stage was implemented using discrete components, having an average quiescent power consumption of 454uW. The complete switched-mode tuning system requires current and voltage sensing, control compensation and PWM generation. A range of analogue and miJ5'ed signal implementations of these subsystems were investigated and it was concluded that at this power level the most significant challenge arises from balancing gate drive losses against the requirement for ultra low conduction losses in the power devices. Experimental results demonstrate that electrical tuning can extend the bandwidth over which a resonant vibration harvester can provide useful DC power, to almost three times that achieved with a simple unity power factor converter synthesising a fixed load resistance.
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Hendrix, Christopher (Christopher M. ). "Feasibility of passive electromagnetic dampers as energy harvesters in large structures." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82816.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 44).
There has been a trend in structural design toward energy efficient design and motion based design. The strategy of motion based design is controlling the movement of structures to meet certain dynamic response requirements by damping the structure. Structural damping dissipates the energy of external loads internally within the structure. A simple idea is to connect the two design strategies to control the motion of a structure while harvesting this dissipated energy by transducing it to electrical energy via passive electromagnetic damping. This study will attempt to determine the feasibility of using passive electromagnetic damping to control the motion and harvest the energy of damping of large scale structures.
by Christopher Hendrix.
M.Eng.
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Kim, Miso. "Materials and device design for MEMS piezoelectric mechanical vibration energy harvesters." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/101863.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 234-245).
Piezoelectric vibration energy harvesters (PVEHs) for microelectromechanical systems (MEMS) have received considerable attention as an enabling technology for self-powered wireless sensor networks. MEMS-PVEHs are particularly attractive because of the potential to deliver power indefinitely and their ability to be integrated concurrently with microfabrication of sensor nodes. A key challenge has been insufficient power and voltage generation for practical applications. Along with research efforts on improved materials, efficient electronics, and fabrication of devices, modeling is an indispensable element in predicting and designing PVEHs. Here, an improved electromechanically-coupled model is developed including the ability to analyze proof mass effects and different electrode configurations. Although essential in microscale devices to move device resonances towards optimal frequency points for harvesting, proof masses have not been treated rigorously in extant work. An improved treatment of a rigid proof mass with rotation, and an exact treatment (two-beam model) of a flexible proof mass, are presented and experimentally verified using a macroscale, symmetric, bimorph, cantilevered PVEH device operating in {3-1} mode with a rigid proof mass, and a micron-scale Si cantilever with a flexible proof mass, respectively. Focused ion beam milling is used to create different flexible proof masses, and atomic force microscopy is used to study the mechanical behavior of micron-scale, single-crystal Si cantilevers. It is found that the two-beam model is necessary for the majority of the proof mass cases considered, especially when considering key power-generation characteristics such as strain developed in the piezoelectric layers. The effects of piezoelectric material properties on device performance are studied via model-based sensitivity analyses to gain insight into the design and selection of optimal piezoelectric materials for power and voltage generation. Notably, and non-intuitively, optimum power either at resonance or antiresonance is independent of the piezoelectric coupling constant of the piezoelectric material, obviating the oft-cited rationale for materials research to increase piezoelectric coupling coefficients. For example, in an exemplary PVEH optimization, maximum power and voltage are obtained at relatively low values (30-40% of bulk PZT, near AlN and ZnO film values) of piezoelectric coupling coefficients. The improved model is used as a multi-variable design tool for designing a novel piezoelectric/ultrananocrystalline diamond (UNCD) heterostructure MEMS-PVEH device. This thesis contributes to the development of MEMS- PVEHs by offering new insights at both the materials and system levels, including optimization findings using different objective functions, such as efficiency. Future work includes application of the modelderived piezoelectric materials design guidelines to aid in the design of optimal MEMS-PVEH systems, fabrication of designed UNCD/piezoelectric-based MEMS-PVEHs, and analytical and experimental studies of both structural and piezoelectric fatigue phenomena for enhanced reliability of PVEHs.
by Miso Kim.
Ph. D.
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Xu, Ruize Ph D. Massachusetts Institute of Technology. "The design of low-frequency, low-g piezoelectric micro energy harvesters." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74954.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 107-112).
A low-frequency, low-g piezoelectric MEMS energy harvester has been designed. Theoretically, this new generation energy harvester will generate electric power from ambient vibrations in the frequency range of 200~30OHz at excitation amplitude of 0.5g. Our previous energy harvester successfully resolved the gain-bandwidth dilemma and increased the bandwidth two orders of magnitude. By utilizing a doubly clamed beam resonator, the stretching strain triggered at large deflection stiffens the beam and transforms the dynamics to nonlinear regime, and increases the bandwidth. However, the high resonance frequency (1.3kHz) and the high-g acceleration requirement (4-5g) shown in the testing experiments limited the applications of this technology. To improve the performance of the current energy harvesters by lowering the operating frequency and excitation level, different designs have been generated and investigated. Moreover, a design framework has been formulated to improve the design in a systematic way with higher accuracy. Based on this design framework, parameter optimization has been carried out, and a quantitative design with enhanced performance has been proposed. Preliminary work on fabrication and testing setup has been done to prepare for the future experimental verification of the new design.
by Ruize Xu.
S.M.
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Xiong, Xingyu. "Development of vibration-based multi-resonance energy harvesters using piezoelectric materials." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/development-of-vibrationbased-multiresonance-energy-harvesters-using-piezoelectric-materials(62d0d760-8b9c-4958-94a9-677b0e57082d).html.
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The development of self-powered wireless sensor networks for structural and machinery health monitoring has attracted considerable attention in the research field during the last decade. Since the low-duty-cycle wireless sensor networks have significantly reduced the power requirements to the range of tens to hundreds of microwatts, it is possible to harvest environmental energy as the power supply instead of using batteries. Vibration energy harvesting using piezoelectric materials has become the most popular technique, which has a good potential to generate adequate power. However, there is a limitation for the conventional beam-shaped harvester designs in real applications due to their limited bandwidth. In order to overcome this limitation, the essential objective of this thesis is to develop harvesters with multi-resonance structures. The multi-resonance harvester with good broadband performance can achieve close resonance frequencies and relatively large power output in each vibration mode. The main tasks and contributions of this thesis are summarised as follows: • A parametric analysis is presented to determine how the modal structural and electromechanical performances of cantilevered beam harvesters are affected by two modal factors designated as mass ratio and electromechanical coupling coefficient (EMCC). The modal performance of using rectangular, convergent and divergent tapered configurations with and without extra masses are systematically analysed by geometric variation using the finite element analysis (FEA) software ABAQUS. • A modal approach using the two modal factors to evaluate the modal performance of harvesters is introduced and a configurational optimization strategy based on the modal approach is developed to pre-select the configurations of multi-resonance harvesters with better modal structural performance and close resonance frequencies in multiple modes. Using this optimization strategy obviates the need to run the full analysis at the first stage. • A novel two-layer stacked harvester, which consists of a base cantilevered beam that is connected to an upper beam by a rigid mass, is developed. By altering the dimensions and the locations of the masses, the two-layer harvester can generate two close resonance frequencies with relatively large power output. The effects of using rectangular, convergent and divergent tapered beam configurations are systematically analysed. • Multi-layer stacked harvesters with up to five layers are developed. The three-layer harvesters with different mass positions, which can generate three close resonance frequencies, are optimized using the configurational optimization strategy. • A novel doubly-clamped multi-layer harvester, which is able to generate five close resonance frequencies with relatively large power output, is developed and thoroughly analysed. • An experimental study of the multi-layer stacked harvester is presented to validate the simulated results and the configurational optimization strategy. • An experimental study of the two-layer stacked harvester using high performance single crystal piezoelectric material PIMNT is presented. The harvester using PIMNT can generate nearly 10 times larger power output and 3.5 times wider bandwidth than using PZT. Besides, by modifying the location of the piezoelectric layer, anti-resonances between two adjacent modes can be eliminated.
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Zhang, Hanlu. "Modeling, simulation, and optimization of miniature tribo-electret kinetic energy harvesters." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC100.
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La récupération d'énergie dans l'environnement ambiant est une bonne solution d'alimentation durable et complémentaire dans certains produits électroniques grand public, réseaux de capteurs distribués sans fil, dispositifs portables ou implantables, systèmes "Internet of Things" avec beaucoup de nœuds, etc. par rapport aux batteries. Les mouvements et les vibrations sont des sources d’énergie les plus disponibles à cet effet. Les dispositifs collectant de l’énergie cinétique à petite échelle sont appelés récupérateurs d'énergie cinétique (RECs). Les RECs avec électrets (E-RECs) sont un type de RECs électrostatiques qui utilisent des électrets (diélectriques avec charges quasi permanentes) comme source de tension de polarisation, et qui peuvent générer de l'électricité grâce à l'effet d'induction électrostatique lorsque la la capacitance des E-RECs varie du fait des mouvements/vibrations. Cette thèse vise à étudier les caractéristiques de sortie transitoires des E-RECs à la fois par des simulations théoriques et des mesures expérimentales, et à optimiser l’efficacité et la puissance de sortie des E-RECs par charge triboélectrique et par d'autres méthodes adaptées à leurs caractéristiques de sortie, qui sont essentielles pour améliorer la performance des E-RECs par mouvements/vibrations.Tout d'abord, les caractéristiques de sortie à amplitude variable d'un E-REC en mode contact-séparation (CS) dans des cycles de travail transitoires sont examinées via les résultats de la simulation basés sur un modèle de circuit équivalent détaillé. Ces caractéristiques de sortie à amplitude variable sont attribuées au décalage du cycle de transfert de charge par rapport au cycle de mouvement d'excitation. Les influences de la condition initiale et de la résistance de charge sur la variation des pics de tension de sortie d'un tribo-électret REC (TE-REC) en mode CS réalisé avec un film électret en polytétrafluoroéthylène (PTFE) one été étudiées en détail et vérifiées à la fois par simulations et expériences.Deuxièmement, une méthode d'optimisation du temps de contact est utilisée pour améliorer la puissance de sortie et l'efficacité du TE-REC en mode CS avec une résistance de charge de 100 MΩ. L'énergie convertie théorique maximale par cycle de travail du TE-REC est analysée. Nous avons aussi étudié les influences de plusieurs facteurs défavorables qui généralement réduiraient la conversion d'énergie par cycle de travail du TE-REC. L’optimisation de l'intervalle d'air maximal et la méthode tribo-charge sont également utilisées pour améliorer la puissance moyenne sortie du TE- REC avec une surface de 4 cm × 4 cm, de ~ 150 μW à ~ 503 μW.Troisièmement, une méthode innovante et facile a été développée pour charger le film polymère électret en éthylène propylène fluoré (FEP) par pelage de ruban adhésif, sans utiliser de source de haute tension électrique. La distribution du potentiel de la surface du film de FEP est fortement modifiée après plusieurs pelages au ruban adhésif. Par conséquence, la tension et le courant de sortie des TE-REC fabriqués avec le film FEP traités sont beaucoup améliorés. Pour un TE-REC flexible d’une surface de 64 cm2 soufflé par du vent, une amélioration évidente d'environ 692% de la puissance de sortie, correspondant 2,5 μW à environ 19,8 μW, a été obtenue par cette méthodeHarvesting energy from the ambient environment is a good sustainable and complementary power supply solution in some consumer electronics, distributed wireless sensor networks, wearable or implantable devices, "Internet of Things" systems with lots of nodes, etc. in comparison with batteries. The ubiquitous kinetic energy in various motions and vibrations is one of the most available energy sources for such a purpose. The electret kinetic energy harvesters (E-KEHs) is one type of electrostatic kinetic energy harvesters using electrets (dielectrics with quasi-permanent charges) as the biasing voltage source, which can generate electricity based on the electrostatic induction effect when the capacitance of the E-KEHs is changed by the motions/vibrations. This thesis aims to investigate the transitory output characteristics of E-KEHs by both theoretical simulations and experimental measurements and to optimize the efficiency and output power of E-KEHs by tribo-charging and other methods adapted to their output characteristics, which are significant to improving the performance of E-KEHs.Firstly, the amplitude-variable output characteristics of a contact-separation (CS) mode E-KEH in transitory working cycles are investigated via the simulation results based on a detailed equivalent circuit model. These amplitude-variable output characteristics are attributed to the lag of the charge-transfer cycle behind the excitation motion cycle. The influences of both the initial condition and the load resistance on the variation in the output voltage peaks of a tribo-electret KEH (TE-KEH) are studied in detail and verified by both simulated and experimental data of a CS mode TE-KEH made with polytetrafluoroethylene (PTFE) electret film.Secondly, based on the analysis of the amplitude-variable output characteristics, a contact time optimization method is used to improve the output power and efficiency of the CS mode TE-KEH with a large load resistance of 100 MΩ. The theoretical maximum output energy per working cycle of the TE-KEH is analyzed. Several usually unfavorable factors that would reduce the practical output energy per working cycle of the TE-KEH are discussed. The maximum air gap optimization and the tribo-charging methods are also used together to further improve the average output power of the 4 cm × 4 cm sized TE-KEH from ~150 μW to ~503 μW.Thirdly, an innovative and facile tape-peeling tribo-charging method is developed to charge the fluorinated ethylene propylene (FEP) polymer film to make electrets without using any high voltage source. The surface potential distribution of the FEP film is apparently changed after several tape-peeling tribo-charging treatments. Consequently, the output voltage and current of TE-KEHs made with the FEP film are greatly improved. For a 64 cm2 sized flexible TE-KEH to harvest kinetic energy from wind, an apparent ~692% improvement in the output power from ~2.5 μW to ~19.8 μW was obtained by the tape-peeling charging method
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Sunduza, Nosipho Gloria. "Poverty alleviation through the development of subsistence harvesters at Ngqushwa Municipality." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/9228.
Full textAbstract:
The broad objective of the study was poverty alleviation through the development of subsistence harvesters at Ngqushwa Municipality. The research objectives were to explore - ways of advancing from being subsistence level producers, opportunities available to these harvesters, if they, (subsistence harvesters), want to be commercialized and what actions do they need to take to become successful businesses. The study was conducted in the the coastal area of Ngqushwa Municipality. The researcher conducted face-to-face interviews with 2 key informants. The respondents provided information on the marine species harvested by the subsistence harvesters of the Ngqushwa Municipality and the type of tools they use for harvesting. They mentioned how subsistence harvesters could advance from subsistence level to producers, about opportunities available to these harvesters, and what actions they need to take if they want to become successful businesses. The key informants also informed the researcher that subsistence harvesters are now classified as Small Scale Fisheries and informed about villages that engage in subsistence harvesting within the Ngqushwa Municipality area. 15 subsistence harvesters were randomly sampled in Polar Park, Qolweni, Gcinisa and Wesley villages which fall under the Ngqushwa Municipality. These harvesters shared their willingness to move from subsistence to commercial fisheries. The use of storytelling interviews (4 subsistence), was also used by the researcher to get more information about their experiences and challenges. The survey was conducted over 7 days. One day in June, 2016 and 6 days in September, 2016. The total number of people interviewed was 21, made up of 2 key informants, 15 subsistence and 4 story telling interviews. The results showed that the community of subsistence harvesters is very discontented because they do not benefit from the sea and the marine resources although they live near the ocean. They also believe that in 22 years of democracy there is no way forward from the government. They are irate as they have witnessed the top down management style from the government. The current subsistence harvesters have little or no formal school education, (23% with no formal schooling at all, 23% with high school education between grades 8 - 12). Without the educational and skills programs from the government the subsistence harvesters will not be able to grow and create further employment opportunities for the rest of the community of Ngqushwa Municipality. The following recommendations have suggested that co-management must come from the community. It must not be people from parliament who do not feel the pain the communities are suffering. The top down approach should stop and a bottom up approach should be implemented, which will allow decisions to be made by the communities involved in harvesting. The government only needs to monitor. They (Government), have good policies, but are they are not monitored. The harvesters need training from the government. There is a need for the formulation of a development forum with learned people, churches, community leaders, young people, women, disabled, and the fishing community all represented. There is also need of support in terms of equipment, boats and education. The government needs to conduct training on fisheries and business management and provide financial support and assistance with business plans.
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Gorial, Bassim Yousif. "Pneumatic methods for the separation of grain and straw." Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315609.
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Goroski, John Michael. "Effects of taxes and age on depreciation: the case of combine harvesters." Thesis, Montana State University, 1990. http://etd.lib.montana.edu/etd/1990/goroski/GoroskiJ1990.pdf.
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Economic depreciation of the total capital stock of a physical asset is determined by the flow of services used in productive activities and by the size of the capital stock. Previous research studies have attempted to analyze economic depreciation by modeling the flow of services. These studies have often failed to fully specify the model by not including important asset specific explanatory variables, and their models were often estimated with restricted functional forms, which implicitly limited the pattern of economic depreciation. This study, on the other hand, uses a flexible functional form which models price as an exponential quadratic function of age, and thus allows the pattern of economic depreciation to be dervied within the model. The behavior of used asset prices are also estimated as an explicit dynamic process which permits a stronger statistical test of the results. In examining the economic depreciation of combine harvesters, this study utilizes specific explanatory variables to account for the effects of changes in the tax code, shocks in demand, and quality and technology differences across combine harvester models. The major empirical results of this study state that depreciation rates are not constant across different ages of combine harvesters and that depreciation rates and patterns are not stable with respect to changes in tax codes. These results present evidence that if further examination of either economic depreciation or optimal replacement problems are to be solved in an internally consistent manner, a more flexible functional form of the used asset price equation must be utilized such as the flexible funtional form used in this study, and changes in the tax code must be included as a specific explanatory variable.
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Wilsey, David Scott. "Business or pleasure : factors motivating northern Minnesota non-timber forest product harvesters /." Diss., ON-CAMPUS Access for University of Minnesota, Twin Cities Click on "Connect to Digital Dissertations, 2002. http://www.lib.umn.edu/articles/proquest.phtml.
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Faisal, Farjana. "Towards the use of piezoelectric energy harvesters in pavement with passing vehicles." SPIE, 2017. http://hdl.handle.net/1993/32084.
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Piezoelectric energy harvesters in the road pavement are developed and studied to collect energy from the passing vehicles. A numerical model based on the Westergaard's stress model is proposed to calculate the three dimensional stress distribution in the pavement and the power generation from the piezoelectric harvesters placed inside the pavement. Piezoelectric patch, plate and beam harvesters are designed. Based on proposed numerical models, simulations are conducted to reveal the effects of vehicle velocity as well as the location and size of the Piezo-electric harvesters on the generated power. Optimally designed plate energy harvester attached with four cantilever harvesters generates up to around 28 W electrical power with the assumption of continuum vehicle passing the pavement by 22.2 m/s. This power can be used to collect enough energy in 2 hours to raise the ice temperature with the thickness of 1 cm, covering a 5 m wide road by 20 degree Celsius.February 2017
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Galbier, Antonio Costante. "Investigation of the Interaction between Energy Harvesters in Pacemakers and the Heart." Thesis, State University of New York at Buffalo, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10255430.
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Embedded piezoelectric energy harvesting (PEH) systems in medical pacemakers have been an attractive and well visited research area. These systems typically utilize different configurations of beam structures with forcing originating from heart beat oscillations. The goal of these systems, at present, is to remove the pacemaker battery, which makes up 60-80% of the unit, and replace it with a sustainable and self-reliant power option. This requires that the energy harvesting system provide sufficient power, 1-3?W, for operating a pacemaker. With emerging technologies encouraging a push towards leadless pacemakers; typical energy harvesting beam structures are becoming inherently coupled with the heart system. The goal of this work is to develop, test, and simulate cantilevered energy harvesters with a linear elastic magnifier (LEM). This research hopes to provide insight into the interaction between pacemaker energy harvesters and the heart. By introducing the elastic magnifier into linear and nonlinear systems oscillations of the tip are encouraged into high energy orbits and large tip deflections. A continuous nonlinear model is derived for the bistable piezoelectric energy harvesting (BPEH) system and a one-degree-of-freedom linear mass-spring-damper model is derived for the elastic magnifier. The elastic magnifier will not consider the damping negligible due to the viscous nature of the heart, unlike most models. For experimental testing a physical model was created for the bistable structure and fashioned to an elastic magnifier. A hydrogel was chosen as the physical model for the LEM. Experimental results have shown that the bistable piezoelectric energy harvester coupled with a linear elastic magnifier (BPEH+LEM) produces more power at certain input frequencies and operates a larger bandwidth than a PEH, BPEH, and a standard piezoelectric energy harvester with the elastic magnifier (PEH+LEM). Numerical simulations were validated by these results showing that the system enters high-energy and high orbit oscillations. It has been shown that BPEH systems implemented in medical pacemakers can have enhanced performance if positioned over the heart.
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Massaguer, Colomer Eduard. "Advances in the modelling of thermoelectric energy harvesters in waste heat recovery applications." Doctoral thesis, Universitat de Girona, 2016. http://hdl.handle.net/10803/398612.
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In this work, we investigate harvesting thermoelectric energy from wasted
heat in fluid networks and propose a generic tool for the simulation and
sizing of thermoelectric energy harvesters, that can be used in industrial
applications to convert expended heat energy into electricity.
Current models found in the literature are often based on very specific
applications or are too general in nature to truly explore the optimization
of a wide range of potential thermoelectric applications. The model
developed in this work is highly customizable permitting the optimization
of a large number of varying systems.
We develop a theoretical model to accurately estimate the recovered
energy considering the nonlinearities of the thermoelectricity and heat
transfer equations. Taking into account that a real thermoelectric energy
harvester always comprises multiple thermoelectric modules placed with
respect to the flow direction, both thermal and electrical series-parallel
configurations have also been considered.
The new model has been analysed and validated under steady and
transient states with experimental data. The proposed energy harvesting
system is easily scalable, to cater to a variety of applications with different requirements, while improving the energy recovery and operational
lifetime of energy sources.
On the other hand, this new model is coded in the TRNSYS environment,
hence it can be used in design, performance optimization and further
application of thermoelectric energy harvesters. The programmed module
will serve as the key component of the software package that will predict
the performance of the thermoelectric heat recovery unit used in common
thermal systemsEn aquest treball s’investiga la recuperació termoelèctrica en xarxes de fluids i es proposa una eina genèrica per a la simulació i dimensionament de recuperadors termoelèctrics, els quals, poden ser utilitzats en aplicacions industrials per convertir l'energia tèrmica residual en electricitat. Els models actuals que es troben en la literatura es basen sovint en aplicacions molt específiques o són massa generals per analitzar realment el comportament de recuperadors en aplicacions reals. El model desenvolupat en aquest treball és altament adaptable pel que permet estudiar un gran nombre de sistemes diferents. S’ha desenvolupat un model teòric per estimar amb precisió l'energia recuperada tenint en compte les no linealitats de les equacions termoelèctriques i de transferència de calor. Tenint en compte que un recuperador termoelèctric comprèn sempre múltiples mòduls termoelèctrics col·locats en respecte a la direcció de flux, ambdues configuracions sèrie-paral·lel tant la tèrmica com l’elèctrica s'han considerat. El nou model ha estat analitzat i validat sota diversos estats estacionaris i transitoris a partir de dades experimentals. El model de recuperador proposat s’ha codificat per tal de treballar en l’entorn TRNSYS, de manera que pot ser utilitzat en el disseny i optimització de recuperadors termoelèctrics, és fàcilment escalable, permet atendre a una gran varietat d'aplicacions i requisits i, per tant, ajudar a la seva implantació en aplicacions reals. Aquest mòdul servirà per predir el comportament de recuperadors de calor termoelèctrics aplicats en sistemes tèrmics convencionals
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Christie, Candice Jo-Anne. "A field investigation of physical workloads imposed on harvesters in South African forestry." Thesis, Connect to this title online, 2006. http://eprints.ru.ac.za/246/.
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Leicht, Joachim [Verfasser], and Yiannos [Akademischer Betreuer] Manoli. "CMOS circuits for electromagnetic vibration energy harvesters : : system modeling, interface design and implementation." Freiburg : Universität, 2019. http://d-nb.info/1193423090/34.
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Hinchet, Ronan. "Electromechanical study of semiconductor piezoelectric nanowires. Application to mechanical sensors and energy harvesters." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT013/document.
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Les systèmes intelligents sont le résultat combiné de différentes avancées en microélectronique et en particulier de l’augmentation des puissances de calcul, la diminution des consommations d’énergie, l'ajout de nouvelles fonctionnalités et de moyens de communication et en particulier à son intégration et application dans notre vie quotidienne. L'évolution du domaine des systèmes intelligents est prometteuse, et les attentes sont élevées dans de nombreux domaines : pour la surveillance dans l'industrie, les transports, les infrastructures et l'environnement, ainsi que dans le logement, l'électronique grand public et les services de soins de santé, mais aussi dans les applications pour la défense et l’aérospatial. Aujourd’hui, l'intégration de plus en plus de fonctions dans les systèmes intelligents les conduisent vers un problème énergétique où l'autonomie devient le principal problème. Par conséquent, il existe un besoin croissant en capteurs autonomes et sources d'alimentation. Le développement de dispositifs de récupération d’énergie et de capteurs autoalimentés est une façon de répondre à ce problème énergétique. Parmi les technologies étudiées, la piézoélectricité a l'avantage d'être compatible avec l'industrie des MEMS. De plus elle génère des tensions élevées et elle possède un fort couplage direct entre les physiques mécaniques et électriques. Parmi les matériaux piézoélectriques, les nanofils (NFs) semi-conducteurs piézoélectriques pourraient être une option prometteuse car ils présentent des propriétés piézoélectriques plus importantes et une plus grande gamme de flexion.Parmi les différents NFs piézoélectriques, les NFs de ZnO et de GaN sont les plus étudiés. A l'échelle nanométrique leurs propriétés piézoélectriques sont plus que doublées. Ils ont l'avantage d'être compatible avec l’industrie microélectronique et raisonnablement synthétisable par des approches top-down et bottom-up. En particulier, nous avons étudié la croissance par voie chimique de NFs de ZnO. Pour les utiliser correctement, nous avons étudié le comportement des NFs de ZnO. Nous avons effectué une étude analytique et des simulations par éléments finis (FEM) d'un NF de ZnO en flexion. Ces études décrivent la distribution du potentiel piézoélectrique en fonction de la force et permettent d’établir les règles d'échelle et de dimensionnement. Ensuite, nous avons développé la caractérisation mécanique par AFM du module de Young de NFs de ZnO et de GaN, puis nous avons effectué des caractérisations piézoélectriques par AFM de ces NFs pour vérifier leur comportement sous des contraintes mécaniques de type flexion. Une fois leur comportement physique compris, nous discutons des limites de notre modèle de NFs piézoélectriques en flexion et nous développons un modèle plus réaliste et plus proche des configurations expérimentales. En utilisant ce nouveau modèle, nous avons évalué le potentiel des NFs de ZnO pour les capteurs de force et de déplacement en mesurant le potentiel généré sous une contrainte, puis, sur la base d’expériences, nous avons évalué l'utilisation de NFs de GaN pour les capteurs de force en mesurant le courant au travers des NFs contraints. De même, nous avons évalué le potentiel de ces NFs pour les applications de récupération d'énergie liées aux capteurs autonomes. Pour bien comprendre la problématique, nous avons étudié l’état de l’art des nano générateurs (NG) et leurs architectures potentielles. Nous analysons leurs avantages et inconvénients, afin de définir une structure de NG de référence. Après une brève étude analytique de cette structure pour comprendre son fonctionnement et les défis, nous avons effectué plusieurs simulations FEM pour définir des voies d'optimisation pour les NG utilisé en mode de compression ou de flexion. Enfin la fabrication de prototypes et leurs caractérisations préliminaires sont présentéesSmart systems are the combined result of different advances in microelectronics leading to an increase in computing power, lower energy consumption, the addition of new features, means of communication and especially its integration and application into our daily lives. The evolution of the field of smart systems is promising, and the expectations are high in many fields: Industry, transport, infrastructure and environment monitoring as well as housing, consumer electronics, health care services but also defense and space applications. Nowadays, the integration of more and more functions in smart systems is leading to a looming energy issue where the autonomy of such smart systems is beginning to be the main issue. Therefore there is a growing need for autonomous sensors and power sources. Developing energy harvesters and self-powered sensors is one way to address this energy issue. Among the technologies studied, piezoelectricity has the advantage to be compatible with the MEMS industry, it generates high voltages and it has a high direct coupling between the mechanic and electric physics. Among the piezoelectric materials, semiconductor piezoelectric nanowires (NWs) could be a promising option as they exhibit improved piezoelectric properties and higher maximum flexion.Among the different piezoelectric NWs, ZnO and GaN NWs are the most studied, their piezoelectric properties are more than doubled at the nanoscale. They have the advantage of being IC compatible and reasonably synthesizable by top-down and bottom-up approaches. Especially we studied the hydrothermal growth of ZnO NWs. In order to use them we studied the behavior of ZnO NWs. We performed analytical study and FEM simulations of a ZnO NW under bending. This study explains the piezoelectric potential distribution as a function of the force and is used to extract the scaling rules. We have also developed mechanical AFM characterization of the young modulus of ZnO and GaN NWs. Following we perform piezoelectric AFM characterization of these NWs, verifying the behavior under bending stresses. Once physics understood, we discuss limitation of our piezoelectric NWs models and a more realistic model is developed, closer to the experimental configurations. Using this model we evaluated the use of ZnO NW for force and displacement sensors by measuring the potential generated, and from experiments, the use of GaN NW for force sensor by measuring the current through the NW. But energy harvesting is also necessary to address the energy issue and we deeper investigate this solution. To fully understand the problematic we study the state of the art of nanogenerator (NG) and their potential architectures. We analyze their advantages and disadvantages in order to define a reference NG structure. After analytical study of this structure giving the basis for a deeper understanding of its operation and challenges, FEM simulations are used to define optimization routes for a NG working in compression or in bending. The fabrication of prototypes and theirs preliminary characterization is finally presented
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Heymanns, Matthias. "Multistable Structures for Broad Bandwidth Vibration-based Energy Harvesters: An Analytical Design Investigation." Phd thesis, Studienbereich Mechanik, Technische Universität Darmstadt, 2015. https://tuprints.ulb.tu-darmstadt.de/5333/1/Dissertation_Heymanns.pdf.
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The field of vibrational energy harvesting aims to transform ambient mechanical energy into electrical energy. For example, this energy can be used to operate autonomous sensor units for structural health monitoring or to supply low power electronic devices. Robust energy harvesters that allow to harvest sufficient energy over a broad frequency range are crucial for these applications. One strategy to increase the bandwidth of energy harvesters and, thus, the robustness is the exploitation of multistable structures. This is due to their feature of showing large amplitude oscillations that result from snap-through actions (inter-well oscillations) in a significant frequency range.
The aim of this thesis is to analyze different multistable energy harvester designs in order to optimize their performance and formulate design criteria. The considered designs are a bistable electromechanical beam, a bistable electromechanical composite plate and a newly proposed design of a multistable plate with four equilibria. Firstly, analytical models for the multistable energy harvesters are presented in order to assess their broad bandwidth harvesting capabilities. Analytical methods are applied to these models to investigate the underlying bifurcation behavior. Based on the analytical investigations, design criteria are formulated to describe the favorable harvesting domain. Numerical simulations are performed to supplement the analytical investigations. The differences of the considered structures are highlighted concerning robust and efficient harvesting by means of numerical simulations for different types of excitation. Experiments are carried out to complement the analytical and numerical analysis. The experiments establish the transferability of the numerical and analytical findings to real-world applications.
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Aponte, Erick. "A Study on Energy Harvesters for Physical Unclonable Functions and Random Number Generation." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78673.
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As the broad implementation and use of wireless sensor nodes in Internet of Things (IOT) devices increase over the years, securing personal data becomes a growing issue. Physical unclonable functions (PUFs) and random number generators (RNGs) provide methods to generate security keys for data encryption. Transducers used in the energy harvesting systems of wireless sensor nodes, can generate the PUFs and RNGs. These transducers include piezoelectric devices (piezo), thermoelectric generators (TEG) and solar cells. This research studies the electrical properties of transducers at normal and low operating levels for electrical responses that can be used in PUF generation and random number generation respectively.
The PUF generation discussed in this study analyzes the resonance frequency of 10 piezos, and the open-circuit voltages of 5 TEGs and 5 solar cells. The transducers are tested multiple times over a 10-day period to evaluate PUF reproducibility and reliability characteristics. The random number generation is accomplished by applying a low-level vibration, thermal or light excitation to each respective transducer. The generated electrical signals are amplified and digitally processed and analyzed using the National Institute of Standards and Technology (NIST) Statistical Test Suite.
The experiment results for the PUF generation are promising and indicate that the piezos are the better choice due to their stable frequency output. Each transducer was able to produce random numbers and pass the NIST tests, but the TEGs passed the NIST tests more often than the other transducers. These results offer a preliminary basis for transducers to be used directly in security applications.Master of Science
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Turner, John Andrew. "A New Approach to Wide Bandwidth Energy Harvesting for Piezoelectric Cantilever Based Harvesters." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/19301.
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This thesis proposes a control system to widen the bandwidth of piezoelectric transducers (PZTs) for vibration energy harvesting while extracting maximum power. A straightforward complex conjugate match achieves maximum power transfer only at a single frequency while requiring an impractically large inductance. The proposed system intends to address these problems. It incorporates a bi-directional DC/DC converter with feed-forward control to achieve a complex conjugate match over a wide range of frequencies. Analysis of the proposed system and simulation results are presented to verify validity of the proposed method.Master of Science
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Schroeder, Christopher. "Exploiting Collective Effects to Direct Light Absorption in Natural and Artificial Light-Harvesters." Thesis, University of Maryland, College Park, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10128741.
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Photosynthesis—the conversion of sunlight to chemical energy—is fundamental for supporting life on our planet. Despite its importance, the physical principles that underpin the primary steps of photosynthesis, from photon absorption to electronic charge separation, remain to be understood in full. Electronic coherence within tightly-packed light-harvesting (LH) units or within individual reaction centers (RCs) has been recognized as an important ingredient for a complete understanding of the excitation energy transfer (EET) dynamics. However, the electronic coherence across units—RC and LH or LH and LH—has been consistently neglected as it does not play a significant role during these relatively slow transfer processes. Here, we turn our attention to the absorption process, which, as we will show, has a much shorter built-in timescale. We demonstrate that the—often overlooked—spatially extended but short-lived excitonic delocalization plays a relevant role in general photosynthetic systems. Most strikingly, we find that absorption intensity is, quite generally, redistributed from LH units to the RC, increasing the number of excitations which can effect charge separation without further transfer steps. A biomemetic nano-system is proposed which is predicted to funnel excitation to the RC-analogue, and hence is the first step towards exploiting these new design principles for efficient artificial light-harvesting.
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Rahimi, Arian. "Design And Implementation Of Low Power Interface Electronics For Vibration-based Electromagnetic Energy Harvesters." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613820/index.pdf.
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For many years batteries have been used as the main power sources for portable electronic devices. However, the rate of scaling in integrated circuits and micro-electro-mechanical systems (MEMS) has been much higher than that of the batteries technology. Therefore, a need to replace these temporary energy reservoirs with small sized continuously charged energy supply units has emerged. These units, named as energy harvesters, use several types of ambient energy sources such as heat, light, and vibration to provide energy to intelligent systems such as sensor nodes. Among the available types, vibration based electromagnetic (EM) energy harvesters are particularly interesting because of their simple structure and suitability for operation at low frequency values (<10 Hz), where most vibrations exits. However, since the generated EM power and voltage is relatively low at low frequencies, high performance interface electronics is required for efficiently transferring the generated power from the harvester to the load to be supplied. The aim of this study is to design low power and efficient interface electronics to convert the low voltage and low power generated signals of the EM energy harvesters to DC to be usable by a real application. The most critical part of such interface electronics is the AC/DC converter, since all the other blocks such as DC/DC converters, power managements units, etc. rely on the rectified voltage generated by this block. Due to this, several state-of-the-art rectifier structures suitable for energy harvesting applications have been studied. Most of the previously proposed rectifiers have low conversion efficiency due to the high voltage drop across the utilized diodes. In this study, two rectifier structures are proposed: one is a new passive rectifier using the Boot Strapping technique for reducing the diode turn-on voltage values
the other structure is a comparator-based ultra low power active rectifier. The proposed structures and some of the previously reported designs have been implemented in X-FAB 0.35 µ
m standard CMOS process. The autonomous energy harvesting systems are then realized by integrating the developed ASICs and the previously proposed EM energy harvester modules developed in our research group, and these systems have been characterized under different electromechanical excitation conditions. In this thesis, five different systems utilizing different circuits and energy harvesting modules have been presented. Among these, the system utilizing the novel Boot Strap Rectifier is implemented within a volume of 21 cm3, and delivers 1.6 V, 80 µ
A (128 µ
W) DC power to a load at a vibration frequency of only 2 Hz and 72 mg peak acceleration. The maximum overall power density of the system operating at 2 Hz is 6.1 µ
W/cm3, which is the highest reported value in the literature at this operation frequency. Also, the operation of a commercially available temperature sensor using the provided power of the energy harvester has been shown. Another system utilizing the comparator-based active rectifier implemented with a volume of 16 cm3, has a dual rail output and is able to drive a 1.46 V, 37 µ
A load with a maximum power density of 6.03 µ
W/cm3, operating at 8 Hz. Furthermore, a signal conditioning system for EM energy harvesting has also been designed and simulated in TSMC 90 nm CMOS process. The proposed ASIC includes a highly efficient AC-DC converter as well as a power processing unit which steps up and regulates the converted DC voltages using an on-chip DC/DC converter and a sub-threshold voltage regulator with an ultra low power management unit. The total power consumption on the totally passive IC is less than 5 µ
W, which makes it suitable for next generation MEMS-based EM energy harvesters. In the frame of this study, high efficiency CMOS rectifier ICs have been designed and tested together with several vibration based EM energy harvester modules. The results show that the best efficiency and power density values have been achieved with the proposed energy harvesting systems, within the low frequency range, to the best of our knowledge. It is also shown that further improvement of the results is possible with the utilization of a more advanced CMOS technology.
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Li, Yang. "Scene Recognition and Collision Avoidance System for Robotic Combine Harvesters Based on Deep Learning." Kyoto University, 2020. http://hdl.handle.net/2433/259052.
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Sewell, Andrew J. "Multirole power units in cereal harvesting : an economic case for adoption." Thesis, University of Newcastle Upon Tyne, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295107.
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