Acoustic power distribution techniques for wireless sensor networks

Recent advancements in wireless power transfer technologies can solve several residual problems concerning the maintenance of wireless sensor networks. Among these, air-based acoustic systems are still less exploited, with considerable potential for powering sensor nodes. This thesis aims to understand the significant parameters for acoustic power transfer in air, comprehend the losses, and quantify the limitations in terms of distance, alignment, frequency, and power transfer efficiency. This research outlines the basic concepts and equations overlooking sound wave propagation, system losses, and safety regulations to understand the prospects and limitations of acoustic power transfer. First, a theoretical model was established to define the diffraction and attenuation losses in the system. Different off-the-shelf transducers were experimentally investigated, showing that the FUS-40E transducer is most appropriate for this work. Subsequently, different load-matching techniques are analysed to identify the optimum method to deliver power. The analytical results were experimentally validated, and complex impedance matching increased the bandwidth from 1.5 to 4 and the power transfer efficiency from 0.02% to 0.43%. Subsequently, a detailed 3D profiling of the acoustic system in the far-field region was provided, analysing the receiver sensitivity to disturbances in separation distance, receiver orientation and alignment. The measured effects of misalignment between the transducers are provided as a design graph, correlating the output power as a function of separation distance, offset, loading methods and operating frequency. Finally, a two-stage wireless power network is designed, where energy packets are inductively delivered to a cluster of nodes by a recharge vehicle and later acoustically distributed to devices within the cluster. A novel dynamic recharge scheduling algorithm that combines weighted genetic clustering with nearest neighbour search is developed to jointly minimise vehicle travel distance and power transfer losses. The efficacy and performance of the algorithm are evaluated in simulation using experimentally derived traces that presented 90% throughput for large, dense networks.Open Acces

ACOUSTIC LOCALIZATION TECHNIQUES FOR APPLICATION IN NEAR-SHORE ARCTIC ENVIRONMENTS

The Arctic environment has undergone significant change in recent years. Multi-year ice is no longer prevalent in the Arctic. Instead, Arctic ice melts during summer months and re-freezes each winter. First-year ice, in comparison to multi-year ice, is different in terms of its acoustic properties. Therefore, acoustic propagation models of the Arctic may no longer be valid. The open water in the Arctic for longer time periods during the year invites anthropogenic traffic such as civilian tourism, industrial shipping, natural resource exploration, and military exercises. It is important to understand sound propagation in the first-year ice environment, especially in near-shore and shallow-water regions, where anthropogenic sources may be prevalent. It is also important to understand how to detect, identify, and track the anthropogenic sources in these environments in the absence of large acoustic sensory arrays. The goals of this dissertation are twofold: 1) Provide experimental transmission loss (TL) data for the Arctic environment as it now exists, that it may be used to validate new propagation models, and 2) Develop improved understanding of acoustic vector sensor (AVS) performance in real-world applications such as the first-year Arctic environment. Underwater and atmospheric acoustic TL have been measured in the Arctic environment. Ray tracing and parabolic equation simulations have been used for comparison to the TL data. Generally good agreement is observed between the experimental data and simulations, with some discrepancies. These discrepancies may be eliminated in the future with the development of improved models. Experiments have been conducted with underwater pa and atmospheric pp AVS to track mechanical noise sources in real-world environments with various frequency content and signal to noise ratio (SNR). A moving standard deviation (MSD) processing routine has been developed for use with AVS. The MSD processing routine is shown to be superior to direct integration or averaging of intensity spectra for direction of arrival (DOA) estimation. DOA error has been shown to be dependent on ground-reflected paths for pp AVS with analytical models. Underwater AVS have been shown to be feasible to track on-ice sources and atmospheric AVS have been shown feasible to track ground vehicle sources

Spacelab 3 Mission Science Review

Papers and abstracts of the presentations made at the symposium are given as the scientific report for the Spacelab 3 mission. Spacelab 3, the second flight of the National Aeronautics and Space Administration's (NASA) orbital laboratory, signified a new era of research in space. The primary objective of the mission was to conduct applications, science, and technology experiments requiring the low-gravity environment of Earth orbit and stable vehicle attitude over an extended period (e.g., 6 days) with emphasis on materials processing. The mission was launched on April 29, 1985, aboard the Space Shuttle Challenger which landed a week later on May 6. The multidisciplinary payload included 15 investigations in five scientific fields: material science, fluid dynamics, life sciences, astrophysics, and atmospheric science

Investigations of ultra shallow junction ion implanted biaxial tensile strained silicon by means of X-Ray, Raman and photoacoustic techniques

The application of strain to the active channel region of the metal-oxide-semiconductor-field-effect-transistor (MOSFET) has become a necessary practice in integrated circuit (IC) fabrication. The introduction of strain allows increased carrier mobilities, and concomitant device performance enhancements, which are independent of MOSFET scaling. Biaxial tensile strained silicon ("-Si), resulting from epitaxial growth of silicon on a Si1!xGex virtual substrate gives rise to enhanced electron mobilities and, for certain dopants, increased electrical activation. For these reasons it is the material of interest in this thesis. The prospects for industrial implementations of "-Si are heavily dependent on the effects of device processing steps, and the controllability of defect and dopant profiles. Of special interest to the current work is the suitability of "-Si subjected to low energy antimony implants and low thermal budget rapid thermal anneal (RTA), for the production of ultrashallow, abrupt junctions, appropriate for future generation source-drain extensions (SDE). Examined in the wider project are the effects of strain on dopant activation and diffusion through Differential Hall and SIMS measurements carried out by project partners. These measurements provide context for the work herein and demonstrate the desirability of "-Si as a n-MOSFET channel material. For our part, the effects of implant and anneal processes are investigated through both high resolution x-ray diffraction and micro-Raman (µ-Raman) spectroscopy. Synchrotron x-ray topography is used to identify the strain relaxation processes in both the "-Si epilayer and the Si1!xGex virtual substrate. Data obtained during the project called into question the validity of traditional µ-Raman interpretations in the context of degenerately doped silicon, under these conditions additional theoretical considerations are necessary. The µ-Raman data presented herein demonstrates sensitivities to both implant damage and to dopant activation and these dependencies are theoretically accouncted for. Finally, Photoacoustic Spectroscopy is shown to be a technique capable of non-destructive detection of ion implant damage within the top ⇠10 nm of the silicon. These uniquely sensitive measurements araise due to the particular experimental set up used which invoke a strong dependence on the thermal interface resistance within the sample

Characterisation Protocol for Liquid- Phase-Synthesised Graphene

Graphene, a two-dimensional honeycomb sp2 carbon lattice has received enormous attention because of the potential for various applications such as the electrodes of photovoltaic devices and batteries, next-generation flexible electronics and even antibacterial coatings. Interest in the application of graphene is mainly due to its unique physical and chemical properties, flexibility, and tuneability of the properties in graphene-based materials. However, while promising applications of graphene are being discussed, the term ‘graphene’ is often misused, and the difficulties in large-scale production of true two-dimensional graphene have further limited its applications. Methods such as top-down solution-processed exfoliation were developed to overcome the obstacles for large-scale graphene production, but these approaches do not yet produce completely delaminated and homogeneous graphene. To monitor and optimise the graphene production process, the development of a fast, standardised and reliable characterisation protocol for large-scale solution-processed graphene is therefore desirable. Among the many characteristics of graphene flakes, the nano-structural features including the lateral dimension, crystal imperfections and the thicknesses of graphene are the most important factors that affect the various properties of graphene. However, though many of the analytical techniques have continuously been improved, methods to obtain and quantify these graphene nano-structural features are still limited. This is owing to the difficulties of visualising the ultra-thin nano-flakes and the fact that many of the properties of graphene are still unknown to be used to identify the material. In this study, a characterisation protocol was proposed to quantify the fundamental nano- structural features of graphene. In all cases, the nano-structural feature was initially characterised by using the most precise technique based on direct imaging from transmission electron microscopy (TEM), the results were being used as benchmarks for the other fast but less direct methods that based on photon-probe techniques. To integrate and assess different characterisation techniques, quantification and statistical analysis of results have been used. By utilising the method proposed, it was found that the lateral dimension distribution of graphene can be rapidly obtained by Dynamic Light Scattering (DLS), especially for flakes smaller than 1000 nm. The crystalline imperfections within graphene can be obtained and quantified by conventional Raman spectroscopy, in which a simple method based on linear correlation and random sampling was proposed to indicate the source of disorder in graphene samples. The result was compared to the TEM study, and the differences were assigned to the uneven distribution of the defects in graphene flakes. The thickness of graphene was characterised via various techniques. Several empirical equations were derived in order to can be rapidly obtained the thickness of graphene. However, it may not be feasible at this stage to develop a method to accurately determine graphene thickness for large-scale characterisation. It was found that the level of graphitic character could be obtained utilising the variation of Raman 2D (G’) band, which is rather more important, and can be used to improve the graphene synthesis process. In summary, the proposed graphene characterisation protocol offers a practical method to integrate and evaluate different characterisation techniques. Also, the protocol development method can be used as a reference point, which can be applied to other materials for developing material-specific characterisation protocols. Nevertheless, it has been shown that such a graphene characterisation protocol has the ability to quantify and differentiate between inhomogeneous solution-processed graphene samples and can be used for optimising the graphene synthesis processes