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The aim of the work described in this thesis is firstly to improve the collection of vibration energy for piezoelectric cantilever harvesters, by a mechanical technique, so that the devices can harvest energy over a wider bandwidth. Secondly to investigate a new circuit topology for achieving complex conjugate load matching to the piezoelectric harvester. The thesis has been divided into two parts - the mechanical approach and the electrical approach. For the mechanical approach, a novel multiresonant beam, comprising piezoelectric fiber composites on a clamped-clamped beam and side mounted cantilevers, was proposed. The side cantilevers are tuned by tip masses to be resonant at different frequencies. A Rayleigh-Ritz model was developed to predict the vibration response of the proposed model multiresonant beam. This model showed that the bandwidth of the multiresonant beam was increased over that of a single cantilever harvester. A multiresonant beam for energy harvesting was experimentally tested and compared with a single cantilever energy harvester. The transmissibility and voltage responses were investigated, the beam showed a wide frequency response between 14.5Hz and 31Hz, whereas the single cantilever only showed one resonant frequency. Therefore the multiresonant beam system is feasible for wide band energy harvesting. For the electrical approach, the task was to investigate complex conjugate impedance matching for the piezoelectric energy harvesters, so that the output impedance from the piezoelectric harvester can be reduced, and maximum energy extracted from the device with a possibility of frequency tuning. A new amplified inductor circuit was proposed to enable the capacitive output impedance of the piezoelectric device to be cancelled. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. The results showed that a variable effective inductance was achieved. However the circuit is lossy due to imperfections within the system, and needs further work to eliminate these imperfections.

Ambient energy harvesting has attracted significant attention over the last years for applications such as wireless sensors, implantable devices, health monitoring systems, and wearable devices. The methods of vibration-to-electric energy conversion can be included in the following categories: electromagnetic, electrostatic, and piezoelectric. Among various techniques of vibration-based energy harvesting, piezoelectric transduction method has received the most attention due to the large power density of the piezoelectric material and its simple architectures. In contrast to electromagnetic energy harvesting, the output voltage of a piezoelectric energy harvester is high, which can charge a storage component such as a battery. Compared to electrostatic energy harvester, the piezoelectric energy harvester does not require an external voltage supply. Also, piezoelectric harvesters can be manufactured in micro-scale, where they show better performance compared to other energy harvesters, owing to the well-established thick-film and thin-film fabrication techniques. The main drawback of the linear piezoelectric harvesters is that they only retrieve energy efficiently when they are excited at their resonance frequencies, which are usually high, while they are less efficient when the excitation frequency is distributed over a broad spectrum or is dominant at low frequencies. High-frequency vibrations can be found in machinery and vehicles could be used as the energy source but, most of the vibration energy harvesters are targeting at low-frequency vibration sources which are more achievable in the natural environment. One way to overcome this limitation is by using the frequency-up-conversion technology via impacts, where the source of the impacts can be one or two stoppers or more massive beams. The impact makes the piezoelectric beam oscillate in its resonance frequency and brings nonlinear behavior into the system.

Au cours de la dernière décennie, nous avons observé à une croissance rapide du nombre d’appareils de communication, et cette tendance devrait se poursuivre tant que les technologies essentielles telles que des objets connectes façonnent l’avenir de technologies d’information et de communication. Cette croissance a entraîné une augmentation considérable de la demande d’énergie, donc l’empreinte carbone de l’écosystème des ICT ne peut plus être ignorée. De plus, dans les systèmes de communication traditionnelle alimentés par batterie, où l’infrastructure énergétique n’est pas disponible après le déploiement, énergie limitée dans la batterie devient le goulot d’étranglement car elle détermine le lifetime de réseau. Alimenter appareil de communication avec des sources d’énergie ambiante, grâce à technologie de récupération l’énergie, non seulement réduit l’empreinte carbone du secteur de ICT mais aussi augmente l’autonomie des réseaux de communication que dépend de la batterie. Un appareil de récupération d’énergie peut piéger l’énergie de l’entourant environnement (sources typiques sont l’énergie solaire, le vent, les vibrations, thermique, etc.). Cependant, variabilité dans temps de l’énergie ambiant modifie la conception de stratégies de communication très différente des systèmes traditionnels. En dehors de la récupération d’énergie, un débit plus élevé peut être obtenu dans un système sans fil en concevant des systèmes de transmission basé sur des informations de canal de propagation. Comme les techniques d’adaptation de canal exigent d’avoir une certaine connaissance de l’état du canal sans fil envoyé au émetteur, l’augmentation du débit vient a un coût de l’estimation de l’information de canal qui consomment des ressources dans un système de communication, particulièrement, l’énergie. En outre, lorsque l’objectif dans un système de communication est à envoyer des informations sur la source à une destination avec au minimum distorsion erreur, des stratégies de transmission et de compression a être conçu sur la base à la fois sur la variable temps des conditions de canal et la statistiques de la source. Cette thèse porte sur la conception de stratégies de transmission prenant en compte le coût de l’obtention des informations d’état de canal (CSI) à l’émetteur, et les statistiques de sources variables dans le temps lorsque la communication dispositifs reposent sur l’énergie récoltée (donc variant dans le temps) des fournitures. / Over the last decade, we have witnessed a rapid growth in the number of communication devices, and this trend is expected to continue as the key technologies such as Internet of Things (IoT), wearable devices, are shaping the future of information and communication technology (ICT) industry. This growth has resulted in a tremendous increase in the energy demand, and hence the carbon footprint of the ICT ecosystem can no longer be ignored. Additionally, in traditional battery powered communication systems where energy infrastructure is not available after deployment, the limited available energy in the battery becomes the bottleneck as it determines the network lifetime. Powering up nodes with ambient energy sources, thanks to the energy harvesting technology, not only reduces the carbon footprint of ICT sector but also increases the autonomy of battery powered communication networks. An energy harvesting node can scavenge energy from the surrounding environment (typical sources are solar, wind, vibration, thermal, etc.). However, time varying nature of the ambient energy makes the design of communication strategies quite different from the traditional communication systems. Besides energy harvesting, higher throughput can be obtained in a wireless communication system by designing transmission schemes on the basis of propagation channel information. As channel adaptation techniques require to have some knowledge of the wireless channel conditions feedbackto the transmitter, the gain in throughput comes at the cost of pilot-based training and feedback which consume resources in a communication system, especially, energy. In addition when the goal in a communication system is to send information about the source to a destination such that mean squared error distortion is minimized, transmission and compression strategies hasto be designed based on both the time varying channel conditions and the source statistics. This dissertation focuses on the design of transmission strategies taking into account the cost of obtaining the channel state information (CSI) at the transmitter, and time varying source statistics when the communication nodes rely on harvested energy (hence time-varying energy) supplies.

Oak decline-induced mortality and failure of oak regeneration have become a concern in upland oak forests in the Missouri Ozarks. This project investigated the effects of timber harvesting on both oak regeneration and mortality of oak residuals following a suite of harvesting treatments in the Missouri Ozarks based on the sixteen-year monitoring data from the Missouri Ozark Forest Ecosystem Project (MOFEP). On dry sites by year 10, clearcutting improved the density of oak reproduction the most, and that intermediate cutting and clearcutting increased the proportion of black oak reproduction with 2% and 3%, respectively in the composition of the forests in the study area. Single-tree selection exacerbated the mortality of oak residuals, group selection and no harvesting had a similar effect on oak residuals. Intermediate cutting improved the survival of residuals the most. This project suggested well-designed silvicultural practices would likely reduce oak mortality and increase understory oak reproduction.

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A data set was compiled from detailed information provided from 26 independent logging contractors from throughout the Eastern United States over a five year period from 2000 to 2004. The age distribution of the logging contractors in the study has increased over time with the percentage of contactors over the age of 55 rising from 15% to 32%. The median age of all equipment including feller-bunchers, skidders, loaders, bulldozers, service vehicles, and haul trucks increased over the period. While the median age of all equipment increased, the age of service and support equipment saw the greatest increase. The total average cost per ton increased 13% over the five year period from $13.99 in 2000 to $16.11 in 2004, due mostly to increases in fuel costs and higher use of contract services. Total production for all firms increased by a net of 450,000 tons over five years.

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No description available.