Electrically tunable piezoelectric bimorph cantilever for energy harvesting

Con la presente tesi viene esaminato un metodo per modificare la frequenza di risonanza di trasduttori piezoelettrici mediante applicazione di carichi elettrici esterni. L'elaborato inizia con la presentazione dei cristalli utilizzati nel lavoro di tesi, concentrandosi sul processo di fabbricazione di un bimorph cantilever impiegato come convertitore elettromeccanico di energia, la cui frequenza di risonanza è modellizzata analiticamente mediante la legge di Newton e il modello di Euler-Bernoulli. Su tale struttura vengono condotte misure mediante shaker elettrodinamico e analizzatore d'impedenza, ai fini di giusticare il modello analitico presentato. Con lo scopo di sincronizzare la frequenza di risonanza del cantilever con la vibrazione dell'ambiente per massimizzare la potenza disponibile, viene proposto un algoritmo MPPT secondo l'approccio Perturba e Osserva (P&O), al quale è fornita in ingresso la tensione efficace di un layer di materiale piezoelettrico. Valutare la sua risposta in tensione, presenta dei limiti applicativi che hanno portato a prendere in considerazione un approccio totalmente diff�erente, basato sullo sfasamento tra la tensione di un trasduttore piezoelettrico e il segnale di accelerazione impiegato come eccitazione. Misure sperimentali sono state condotte con l'obiettivo di validare l'efficacia di quest'ultimo approccio qualora si voglia sincronizzare la frequenza di risonanza dei piezo con segnali di vibrazione reali.

Piezoelectric energy harvesting using blood-flow-like excitation for implantable devices

The goal of this research is to produce a system for powering medical implants to increase the lifetime of the implanted devices and reduce the battery size. The system consists of a number of elements – the piezoelectric material for generating power, the device design, the circuit for rectification and energy storage. The piezoelectric material is analysed and a process for producing a repeatable high quality piezoelectric material is described. A full width half maximum (FWHM) of the rocking curve X-Ray diffraction (XRD) scan of between ~1.5° to ~1.7° for test wafers was achieved. This is state of the art for AlN on silicon and means devices with good piezoelectric constants can be fabricated. Finite element modelling FEM) was used to design the structures for energy harvesting. The models developed in this work were established to have an accuracy better than 5% in terms of the difference between measured and modelled results. Devices made from this material were analysed for power harvesting ability as well as the effect that they have on the flow of liquid which is an important consideration for implantable devices. The FEM results are compared to experimental results from laser Doppler vibrometry (LDV), magnetic shaker and perfusion machine tests. The rectifying circuitry for the energy harvester was also investigated. The final solution uses multiple devices to provide the power to augment the battery and so this was a key feature to be considered. Many circuits were examined and a solution based on a fully autonomous circuit was advanced. This circuit was analysed for use with multiple low power inputs similar to the results from previous investigations into the energy harvesting devices. Polymer materials were also studied for use as a substitute for the piezoelectric material as well as the substrate because silicon is more brittle.

Vibration based health monitoring of civil infrastructure using energy harvesting techniques

The use of structural health monitoring of civil structures is ever expanding and by assessing the dynamical condition of structures, informed maintenance management can be conducted at both individual and network levels. With the continued growth of information age technology, the potential arises for smart monitoring systems to be integrated with civil infrastructure to provide efficient information on the condition of a structure. The focus of this thesis is the integration of smart technology with civil infrastructure for the purposes of structural health monitoring. The technology considered in this regard are devices based on energy harvesting materials. While there has been considerable focus on the development and optimisation of such devices using steady state loading conditions, their applications for civil infrastructure are less known. Although research is still in initial stages, studies into the uses associated with such applications are very promising. Through the use of the dynamical response of structures to a variety of loading conditions, the energy harvesting outputs from such devices is established and the potential power output determined. Through a power variance output approach, damage detection of deteriorating structures using the energy harvesting devices is investigated. Further applications of the integration of energy harvesting devices with civil infrastructure investigated by this research includes the use of the power output as a indicator for control. Four approaches are undertaken to determine the potential applications arising from integrating smart technology with civil infrastructure, namely • Theoretical analysis to determine the applications of energy harvesting devices for vibration based health monitoring of civil infrastructure. • Laboratory experimentation to verify the performance of different energy harvesting configurations for civil infrastructure applications. • Scaled model testing as a method to experimentally validate the integration of the energy harvesting devices with civil infrastructure. • Full scale deployment of energy harvesting device with a bridge structure. These four approaches validate the application of energy harvesting technology with civil infrastructure from a theoretical, experimental and practical perspective.

Wireless Networks with Energy Harvesting and Power Transfer: Joint Power and Time Allocation

In this letter, we consider wireless powered communication networks which could operate perpetually, as the base station (BS) broadcasts energy to the multiple energy harvesting (EH) information transmitters. These employ “harvest then transmit” mechanism, as they spend all of their energy harvested during the previous BS energy broadcast to transmit the information towards the BS. Assuming time division multiple access (TDMA), we propose a novel transmission scheme for jointly optimal allocation of the BS broadcasting power and time sharing among the wireless nodes, which maximizes the overall network throughput, under the constraint of average transmit power and maximum transmit power at the BS. The proposed scheme significantly outperforms “state of the art” schemes that employ only the optimal time allocation. If a single EH transmitter is considered, we generalize the optimal solutions for the case of fixed circuit power consumption, which refers to a much more practical scenario.

Rate Maximization of Decode-and-Forward Relaying Systems with RF Energy Harvesting

We consider a three-node decode-and-forward (DF) half-duplex relaying system, where the source first harvests RF energy from the relay, and then uses this energy to transmit information to the destination via the relay. We assume that the information transfer and wireless power transfer phases alternate over time in the same frequency band, and their time fraction (TF) may change or be fixed from one transmission epoch (fading state) to the next. For this system, we maximize the achievable average data rate. Thereby, we propose two schemes: (1) jointly optimal power and TF allocation, and (2) optimal power allocation with fixed TF. Due to the small amounts of harvested power at the source, the two schemes achieve similar information rates, but yield significant performance gains compared to a benchmark system with fixed power and fixed TF allocation.

RF energy harvesting two-way cognitive DF relaying with transceiver impairments

This paper analyzes the impact of transceiver impairments on outage probability (OP) and throughput of decode-and-forward two-way cognitive relay (TWCR) networks, where the relay is self-powered by harvesting energy from the transmitted signals. We consider two bidirectional relaying protocols namely, multiple access broadcast (MABC) protocol and time division broadcast (TDBC) protocol, as well as, two power transfer policies namely, dual-source (DS) energy transfer and single-fixed-source (SFS) energy transfer. Closed-form expressions for OP and throughput of the network are derived in the context of delay-limited transmission. Numerical results corroborate our analysis, thereby we can quantify the degradation of OP and throughput of TWCR networks due to transceiver hardware impairments. Under the specific parameters, our results indicate that the MABC protocol achieves asymptotically a higher throughput by 0.65 [bits/s/Hz] than the TDBC protocol, while the DS energy transfer scheme offers better performance than the SFS policy for both relaying protocols.

Impact of primary networks on the performance of energy harvesting cognitive radio networks

In this paper, we investigate the effect of of the primary network on the secondary network when harvesting energy in cognitive radio in the presence of multiple power beacons and multiple secondary transmitters. In particular, the influence of the primary transmitter's transmit power on the energy harvesting secondary network is examined by studying two scenarios of primary transmitter's location, i.e., the primary transmitter's location is near to the secondary network and the primary transmitter's location is far from the secondary network. In the scenario where the primary transmitter locates near to the secondary network, although secondary transmitter can be benefit from the harvested energy from the primary transmitter, the interference caused by the primary transmitter suppresses the secondary network performance. Meanwhile, in both scenarios, despite the fact that the transmit power of the secondary transmitter can be improved by the support of powerful power beacons, the peak interference constraint at the primary receiver limits this advantage. In addition, the deployment of multiple power beacons and multiple secondary transmitters can improve the performance of the secondary network. The analytical expressions of the outage probability of the secondary network in the two scenarios are also provided and verified by numerical simulations.

The effect of hook size on the catch rate and size of the Nile perch Lates niloticus (Linne) fishery in the Napoleon Gulf, Lake Victoria, Uganda

This study was undertaken in Napoleon gulf, Lake Victoria Uganda from July – December 2009. It was conducted in four landing sites; Bukaya (0.41103N, 33.19133E), Bugungu (0.40216N, 33.2028E), Busana (0.39062N, 33.25228E) and Kikondo (0.3995N, 33.21848E) all from Buikwe district (Formerly part of Mukono district). The main aim was to determine the effect of both hook size and bait type on the catch rate (mean weight) and size composition of Nile perch (Lates niloticus) (LINNE) fishery in the Napoleon Gulf, Lake Victoria. The main hook sizes investigated during the experiment were 7, 8, 9, 10, 11 and 12 that were dominantly used in harvesting Nile perch in Napoleon Gulf, Lake Victoria. In this study length, weight and bait type data were collected on site from each boat at that particular fishing spot; since most fishermen in the Napoleon Gulf could sell their fish immediately the catch is caught there and then. The results indicated a total of 873 Nile perch fish samples collected during the study. Statistical tests, descriptive statistics, regression and correlation were all carried out using the Statistical Package for the Social Sciences (SPSS) in addition to Microsoft excel. The bait types in the Gulf ranged from 5-10 cm Total length (TL) haplochromine, 24.5-27 cm TL Mormyrus kannume and 9-24 cm TL Clarias species. The bait types had a significant effect on the catch rate and also on the size composition the fish harvested measured as Total length (ANCOVA F=8.231; P<0.05) despite the fact that bait type had no influence on mean weight of fish captured (ANCOVA F=2.898; P>0.05). Hook sizes used by the fishers had a significant effect on the both the size (TL) composition (ANCOVA F=3.847; P<0.05) and the mean weight (ANCOVA F=4.599; P<0.005) of the Nile perch captured. Investigations indicated hook sizes seven (7) and eight (8) were the ones that harvested the Nile perch above the slot size of 50 cm total length. In general hook sizes indicated to be the main drive in the harvesting of the Nile perch though bait type also contributed toward that. Generally there is need for management to put a law in place on the minimum hook size to be used on the harvesting of the Nile perch and also monitored by the Fisheries Management as a regulatory measure. In addition to that aquaculture should be encouraged to farm the fish for bait at a higher scale in the region in order to avoid depleting the wild stocks already in danger of extinction. Through this kind of venture, both biodiversity conservation and environmental sustainability will be observed in the Lake Victoria basin.

Protein feeding of Queensland fruit fly Bactrocera tryoni and cucumber fly Zeugodacus cucumis (Diptera: Tephritidae) on non-host vegetation: effect of plant species and bait height

Perimeter-baiting of non-crop vegetation using toxic protein baits was developed overseas as a technique for control of melon fly, Zeugodacus (Zeugodacus) cucurbitae (Coquillett) (formerly Bactrocera (Zeugodacus) cucurbitae), and evidence suggests that this technique may also be effective in Australia for control of local fruit fly species in vegetable crops. Using field cage trials and laboratory reared flies, primary data were generated to support this approach by testing fruit flies' feeding response to protein when applied to eight plant species (forage sorghum, grain sorghum, sweet corn, sugarcane, eggplant, cassava, lilly pilly and orange jessamine) and applied at three heights (1, 1.5 and 2 m). When compared across the plants, Queensland fruit fly, Bactrocera tryoni (Froggatt), most commonly fed on protein bait applied to sugarcane and cassava, whereas more cucumber fly, Zeugodacus (Austrodacus) cucumis (French) (formerly Bactrocera (Austrodacus) cucumis), fed on bait applied to sweet corn and forage sorghum. When protein bait was applied at different heights, B. tryoni responded most to bait placed in the upper part of the plants (2 m), whereas Z. cucumis preferred bait placed lower on the plants (1 and 1.5 m). These results have implications for optimal placement of protein bait for best practice control of fruit flies in vegetable crops and suggest that the two species exhibit different foraging behaviours.

Harvesting and Collection of Animal Forest Species

The harvest and trade of corals and other benthic organisms from the world’s shallow tropical reefs is a lucrative industry that can have positive socioeconomic benefits for communities while supplying the increasing demand specimens for aquaria and curios. For most countries, this trade has historically been almost entirely unregulated. More recently, in response to concerns about the rapid decline of some reefs in the face of anthropogenic and natural pressures, as well as indications of depletions and even localized extinctions of some species caused by harvesting, there have been attempts to improve the sustainability of the industry. Both developing and developed countries face different impediments to this reform, the most pressing and common of which is the lack of reliable data on world trade through CITES. Thereafter, differences in the processes through which reform can be implemented are based principally on the length of the supply chain from collection to export, the degree of industry stewardship, and resourcing. The coral collection fishery in Queensland, Australia, provides an example where continual improvements in reporting and risk assessments and adopting a comanagement approach are delivering better adaptive management of the resource, although the on-ground sustainability benefits of this approach are still to be tested. A simpler approach to sustainable use of coral is to favor the replacement of wild harvested specimens with those bred or grown entirely in an aquaculture facility (as opposed to merely collected and then grown out in culture). Yet there are major impediments to this change, including the dependence of many public aquaria on the same sources as the hobbyist community, difficulties of culturing some species in captivity, and infrastructure costs. Nevertheless, this approach will likely play an important part in reef conservation efforts in the future.

Prevalence and characterization of Salmonella spp. in three shellfish-harvesting areas in France

Shellfish farming is an important economic activity in the Brittany and Normandy regions. However, a part of the production sites corresponds to relatively sensitive areas where the presence of faecal microorganisms is a major concern for shellfish and constitutes a possible health risk. Indeed, shellfish bioaccumulates in their tissues pathogenic contaminants present in water and can cause food-borne diseases such as salmonellosis. During a two-year study, we evaluated the presence of faecal indicators, measured the prevalence of Salmonella spp., isolated and characterized Salmonella spp. from three French shellfish-harvesting areas (shellfish and sediment) and their watersheds (from river water samples).

Energy Cooperation in Energy Harvesting Communication Systems

In energy harvesting communications, users transmit messages using energy harvested from nature. In such systems, transmission policies of the users need to be carefully designed according to the energy arrival profiles. When the energy management policies are optimized, the resulting performance of the system depends only on the energy arrival profiles. In this dissertation, we introduce and analyze the notion of energy cooperation in energy harvesting communications where users can share a portion of their harvested energy with the other users via wireless energy transfer. This energy cooperation enables us to control and optimize the energy arrivals at users to the extent possible. In the classical setting of cooperation, users help each other in the transmission of their data by exploiting the broadcast nature of wireless communications and the resulting overheard information. In contrast to the usual notion of cooperation, which is at the signal level, energy cooperation we introduce here is at the battery energy level. In a multi-user setting, energy may be abundant in one user in which case the loss incurred by transferring it to another user may be less than the gain it yields for the other user. It is this cooperation that we explore in this dissertation for several multi-user scenarios, where energy can be transferred from one user to another through a separate wireless energy transfer unit. We first consider the offline optimal energy management problem for several basic multi-user network structures with energy harvesting transmitters and one-way wireless energy transfer. In energy harvesting transmitters, energy arrivals in time impose energy causality constraints on the transmission policies of the users. In the presence of wireless energy transfer, energy causality constraints take a new form: energy can flow in time from the past to the future for each user, and from one user to the other at each time. This requires a careful joint management of energy flow in two separate dimensions, and different management policies are required depending on how users share the common wireless medium and interact over it. In this context, we analyze several basic multi-user energy harvesting network structures with wireless energy transfer. To capture the main trade-offs and insights that arise due to wireless energy transfer, we focus our attention on simple two- and three-user communication systems, such as the relay channel, multiple access channel and the two-way channel. Next, we focus on the delay minimization problem for networks. We consider a general network topology of energy harvesting and energy cooperating nodes. Each node harvests energy from nature and all nodes may share a portion of their harvested energies with neighboring nodes through energy cooperation. We consider the joint data routing and capacity assignment problem for this setting under fixed data and energy routing topologies. We determine the joint routing of energy and data in a general multi-user scenario with data and energy transfer. Next, we consider the cooperative energy harvesting diamond channel, where the source and two relays harvest energy from nature and the physical layer is modeled as a concatenation of a broadcast and a multiple access channel. Since the broadcast channel is degraded, one of the relays has the message of the other relay. Therefore, the multiple access channel is an extended multiple access channel with common data. We determine the optimum power and rate allocation policies of the users in order to maximize the end-to-end throughput of this system. Finally, we consider the two-user cooperative multiple access channel with energy harvesting users. The users cooperate at the physical layer (data cooperation) by establishing common messages through overheard signals and then cooperatively sending them. For this channel model, we investigate the effect of intermittent data arrivals to the users. We find the optimal offline transmit power and rate allocation policy that maximize the departure region. When the users can further cooperate at the battery level (energy cooperation), we find the jointly optimal offline transmit power and rate allocation policy together with the energy transfer policy that maximize the departure region.