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The work presented in this thesis concerns the generation of sound via heat; namely, the thermoacoustic effect. This heat is typically provided by electric heating in thin film devices, resulting in non-resonant, broadband sound generation. The aim of this work is to develop a deeper understanding of the mechanisms behind this process, as well as identify potential applications. This is achieved via analytical and numerical simulations, and experimental measurements. A novel analytical model is derived for describing the sound generated by thermoacoustic sources. This is validated by simulation, as well as electrical, thermal and acoustic measurements of a variety of sources. Multiple sources are also considered, in the context of acoustic phased arrays. It is found that thermoacoustic sources can successfully reproduce typical phased array behaviour, such as beam forming and steering. It is shown that the unique characteristics of this transduction method make thermoacoustic sources highly favourable for this application. In particular, the sources are non-reciprocal, eliminating issues with element cross-talk. The thermal profile is spatially dependent on the local current flow, which offers the ability to define thermal sources by confining the current to specific regions in the film, such that a full phased array can be produced using a single film. Electrical coupling between elements, due to the nonlinearity of the source, results in an additional sound source that is highly sensitive to the configuration of the array. It is shown how this coupling can be used to infer properties of the array elements themselves by measuring the generated sound. A new method of thermoacoustic generation via thermoelectric effects is also explored. Measurements using thermocouple devices show that this results in linear sound generation, at the source fundamental frequency, due to the reversible nature of the effect. This reversibility also presents opportunities to further optimise sound output via dynamic control of the device temperature.

Over the last few decades there has been strong interest in quantum information systems based on photonic qubits. Devices able to emit pure single-photon states on demand and detect incoming single photons in the system are fundamental building blocks for the realisation of a quantum photonic scheme. Advances in controlling single carriers have made it possible to transport single electrons using surface acoustic waves (SAWs). In a lateral n-i-p junction SAW-driven single-electron transport can be exploited to pump single electrons across the junction and generate single photons. In this work, devices have been developed in which both electrons and holes can be induced in an undoped GaAs/AlGaAs 15nm quantum well by gates to form a lateral n-i-p junction. The junction is confined into a quasi-1D channel laterally by etching and side gates. Light emission is observed when a 1 or 3 GHz SAW drives a current, by pumping electrons over the potential hill in the intrinsic region. SAW-driven electroluminescence has been characterised in the regime where less than one electron is transported per cycle on average. Time-resolved electroluminescence has been used to extract the electron recombination time and to quantify the contributions from electromagnetic crosstalk and the SAW. In a device without significant crosstalk, the degree of second-order coherence, g(2)(0) , shows the signature of antibunching. Hole SAW-pumping has been investigated as an alternative to electron pumping, showing a shorter recombination time. The dynamics has been further investigated with time-resolved and energy measurements at the junction, using a sub-micron positioner with lens assembly to scan along the pumping direction. A key requirement for practical quantum devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Using the same type of heterostructure, photons are detected by collecting and measuring the photo-generated carriers. An external light source sends photons into the system, and when they are absorbed in the quantum well, they create electron-hole pairs. The photo-generated carriers are separated and transported by a SAW together with an electric field applied by gates on the surface. The carriers are then collected by ohmic contacts, in order to extract information about the number of photons absorbed. Using the same 15nm GaAs/AlGaAs quantum well as for the single- photon source, an acousto-electric photon detector has been realised and characterised. Single-photon sensitivity can be achieved by measuring the photo-generated charges at single-particle level. The possibility to include single-electron and single-hole charge readout using quantum dots and quantum point contacts has been investigated.

The compositions in this portfolio have been inspired by magic, nature, spirituality, boundaries, perception and the self. The themes are explored in two ways: either directly within the works, or through un-scored live performances and field recordings. The idea of using composition as a way of identifying and understanding our deeply subjective experience of being human is developed within these pages. A suggestion is made that both composition and improvisation can be used as part of an overall holistic approach that helps bridge and integrate the physical material world of nature and everyday life with the non-physical world of dreams, alternative realities and magic. Many cultural theorists, philosophers and writers have noted that the modern age in which we live has resulted in a sense of existential dislocation and disconnection between people. Within this portfolio an attempt is made to address this disconnect. Within the works themselves are pieces inspired by specific locations or specific spiritual traditions from around the world. Many of the pieces are also directly inspired by my own explorations of nature and how this affects and relates to the inner self. The pieces are acoustic in the main, but some have electronic elements. Many of the pieces require unconventional concert hall layouts in an attempt to experiment with audience perception and boundaries and other pieces require the performances to take place in outdoor locations at specific times of the day or year.

Pipelines are considered to be the safest and most economical way of transporting liquid and gas over a long distance. They are used for transporting crude oil and natural gas in process industries, for water transportation and distribution systems in urban and rural areas, for transporting aviation fuel and hydraulic piping as well as air pressure chambers in aircraft. Leaking pipelines can lead to spillage of hydrocarbon fluid into the surrounding environment, and consequently result in fire or outright explosion of the pipeline system as well as production loss, damage to the environment and potential loss of lives. Therefore, accurately identifying and predicting the location and growth of defects are essential and enable the operator to assess and actively manage the integrity of the pipelines. Current leakage detection methods use several non-destructive testing methods such as magnetic particle inspection, radiographic, ultrasonic, pressure transient and acoustic signal methods. This thesis presents acoustic wave propagation-based methods to identify leakage and blockage in pipe systems. In the study, the acoustic finite-element analysis (AFEA) method is employed to simulate acoustic wave propagation in fluid-filled pipes with leakage and blockage but without flow. Computational fluid dynamics (CFD) analysis was also employed to simulate acoustic wave propagation in fluid-filled pipes with leakage and blockage under flow conditions. In addition, experimental testing was conducted to validate some of the numerical results. The experiments consisted of the measurement of acoustic wave propagation in an air-filled pipe with leakage and blockage. The main investigations and contributions of the thesis are summarised as follows, 1) An efficient finite element analysis (FEA) procedure to simulate acoustic wave propagation in fluid-filled pipes is developed. The developed technique overcomes the large errors that occur in the numerical predictions of acoustic wave propagation. The use of different acoustic element types of 2D-like and 3D formulations, and of linear and quadratic interpolations, are investigated in order to deduce the most accurate acoustic FEA approach, and thereby, to minimise the errors. 2) The CFD technique is applied to simulate acoustic wave propagation and reflectometry in a fluid-filled pipe with flow. This is a novel approach of using CFD to predict the acoustic wave propagation in a pipeline in the presence of flow. 3) AFEA and CFD were employed to simulate acoustic wave propagation and reflectometry in a fluid-filled pipe with and without flow. The Time of Flight approach was used on the predicted acoustic waveforms for the pipes with leakage in order to identify the presence of leakage and to predict the size and location of the leakage in the fluid-filled pipe in the presence of flow. 4) Detection of blockage from the predicted data obtained from the CFD and FEA simulation of acoustic wave propagation/reflection in air-filled pipelines without mean flow. Also, the CFD technique was also used to simulate the acoustic wave propagation/reflection in air-filled pipelines with mean flow. Furthermore, the Time of Flight approach was used to identify size and locate the blockage from the simulated data. 5) The experimental measurements of acoustic wave propagation in a straight air-filled intact pipe and air-filled pipes with leakage. The Time of Flight approach was employed to identify size and locate the blockage from the simulated data. Furthermore, the measured and simulated results are compared to validate the simulated results.

Early detection of defects in the commercial piping system is important in preventing large and expensive repairs due to huge unprecedented failure caused by corrosion, blockage or structural deformation. Over the years, various non-destructive inspection methods were used within the multimillion oil and gas industry to prevent losses in both people and money. Studies have been done on stable isotropic media by means of studying the ultrasonic guided test. The dispersive nature of propagation within solid media requires diagnoses from technicians with great experiences, in interpreting the signals acquired through the available sensors and limited to a short distance inspection due to the high attenuation effect. Meanwhile, acoustic pulse reflectometry (APR) within the travelling fluid medium offers an on-line long-range detection potential in a simpler plane wave solution. Although the use of current APR method for locating the non-conformity within a pipeline is straight forward using flight time analysis, the reconstruction knowledge of the blockages or leakages from the response is limited. The incoming input and the response signature are in need of greater understanding. Therefore, in this research, the time domain reflectometry was investigated for various acoustic wave reflections from defects within a pipeline system by means of analytical solution, experimental procedures, and finite element analysis. The travelling potential of input pulse was initially studied for various frequency and amplitude using analytical model, and later modelled in fluid-solid-interface module within 3-D finite element software. The cut off limit of plane wave frequency before higher order mode excitation was determined. Based on the plane wave excitation frequency limit, suitable frequency range of input pulse for long pipeline was further investigated by designing sensitivity analysis test rig. A modification was introduced to the governing attenuation equation for plane wave model of various diameters by exponentially fitting the experimental peak decay of propagating input pulse results, and later adopted into the analytical reconstruction of blockage geometry. Blockages of different sizes, porosity and length were introduced in the experiment to understand the propagation of acoustic wave within the pipe and its echoed signals from non-conformity. Classifications of blockage and length based on the acquired responses were developed using time and frequency domain analysis and compared to the analytical model. Responses from open end excitation were then used as the input to the classification of blockage parameters and trained using neural network for faster processing. This thesis narrowed the gap of knowledge by establishing the methodology for attenuation coefficient using the curve fitting method of multiple pipe reflection, the classifying method of blockage within a pipeline and the training of neural network data from finite element analysis simulation. The results show a great improvement to the detection and re-construction techniques for blockage percentage and length based on the signature of responses for pipeline inspection using APR. The research established different input signals responses, experimental model for determination of defects in pipe and new empirical determination for attenuation coefficient for propagating sound pulse in pipe using single sensor. All these findings will be great input to field application procedures for pipeline inspection.

The work presented in this thesis studies acoustic perturbations in slowly varying pipes. The slow variation is introduced in the form of a small parameter ${\epsilon}$ and through this in turn gives rise to a slow axial scale $X$ such that $X = {\epsilon}x$ where $x$ is the normal axial coordinate. This allows an asymptotic approach and the WKB method is used to solve the subsequent mathematical problems. The first deals with the existence of a trapped mode in a hard-walled pipe of varying radius conveying fluid. For the derived leading order propagating mode solution, its amplitude becomes singular at transition points $X_{t}$ and $X_{t'}$ where $X_{t} > 0$ and $X_{t'} < 0$ and thus is unable to propagate past these points. Because of the break down in the solution, this leads to the theory that in the neighbourhood of these points there exists a boundary layer in which the original assumption about having slow variation does not hold. By first seeking the thickness of the layer, valid solutions can then be derived and then matched to the outer solutions in order to produce a uniform solution which holds for the entire axial domain. Once this is achieved, it is then used to derive trapped mode solutions. In this case, the theory used is that of two single turning points which are then combined to obtain the full solution. It is illustrated through consideration of examples and the dependence on ${\epsilon}$ is also shown through various plots. This problem will be considered for a symmetric and asymmetric duct and for differing duct parameters. Problems may arise when the two turning points lie close together and so we seek to improve on the method used by deriving a solution to trapped modes encompassing both turning points, which will be proposed together with some illustrations in order to justify its use and reliability. Next, the case of mode propagations on a thin elastic shell of varying radius conveying fluid is studied. The acoustic solutions of a straight shell in vacuo are first briefly reviewed and then built up by the addition of radius variation and the presence of a stationary fluid. The work presented first outlines the analysis for wave propagation in a slowly-varying thin elastic shell in vacuo. It is found that the shell and the fluid terms are coupled through the fluid pressure term, which is added to the equation governing the radial shell displacements since the pressure is assumed to affect radial motion only. Once the newly corrected equation for the radial shell displacements has been obtained, together with the axial and azimuthal displacements equations, this new system of governing equations is then separated into leading order ${\epsilon}^{0}$ and first order ${\epsilon}^{1}$ systems. In order to simplify the calculations, only the zeroth azimuthal order $m = 0$ will be studied here. With this simplification, a notable result is that the solutions of the torsional motion is decoupled from the axial and radial solutions. Once the dispersion equation is extracted from the leading order system, it can be seen that the axial and radial solutions are in fact coupled. The solution to the in vacuo with varying radius problem is first briefly presented and it is then followed by the solution to the fluid inclusion problem with varying radius, which makes up the main part of this section. The solution is studied for various frequencies and at various points along the shell. In addition, the axial and radial components of the first three modes are examined along with their amplitudes and energy distributions. Finally, mean flow is added and the same analysis is carried out, paying particular attention to the differences which arise in comparison to the stationary flow case.

The original work presented in this thesis pertains to the design and characterisation of resonant-cavity-based acoustic metamaterials, with a focus on airborne sound. There are five separate experimental chapters, each with a unique approach to the design of periodic structures that can support and manipulate air-bound acoustic surface waves via diffractive coupling between resonant-cavities. The first two chapters concern measurement of the acoustic transmission though various kinds of periodic slit-arrays, whilst the latter three chapters utilise a near-field imaging technique to directly record and characterise the dispersion of trapped acoustic surface waves. The first experimental chapter investigates the effect that thermodynamic boundary layers have on the Fabry-Perot-like cavity resonances that are so often utilised in acoustic metamaterial design. At audio frequencies, these boundary layers have a decay length that is typically more than two orders of magnitude smaller than the width of the resonating slit-cavities, hence it may naively be assumed that their effect can be ignored. However, by studying in detail the effect that reducing slit-cavity width has on the frequency of the measured cavity-resonance, for both a single slit cavity and a slit-cavity array, it is found that these boundary layer effects become significant on a far larger scale than their characteristic thickness. This is manifested in the form of a reduction in the resonant frequency as the slit-width is narrowed. Significant attenuation of the resonance and a 5% reduction in the effective speed of sound through the cavity is measured when the boundary layers form only 5% of the total width of each slit. Hence, it is both shown that the prevalent loss free treatment of acoustic slit-cavities is unrealistic, and that one may control the effective speed of sound through the slit-cavities with a simple change in slit-width. The second chapter explores the effect of ‘compound’ grating structure on trapped acoustic surface waves, a compound grating having a basis comprised of more than one resonating element. The angle dependent acoustic transmission spectra of four types of aluminium slit-array are recorded, and for the compound gratings, it is found that sharp dips appear in the spectra that result from the excitation of a ‘phase-resonance’. This occurs as new degrees-of-freedom available to the acoustic near-field allow the fields of adjacent cavities within a unit-cell to be both out-of-phase and strongly enhanced. By mapping the transmission spectra as a function of in-plane wavevector, the dispersions of the modes supported by each sample are determined. Hence, the origin of the phase-resonant features may be described as acoustic surface waves that have been band-folded back into the radiative regime via diffraction from higher in-plane wavevectors than possible on a simple grating. One of the samples is then optimised via numerical methods that account for thermodynamic boundary layer attenuation, resulting in the excitation of a sharp, deep transmission minimum in a broad maximum that may be useful in the design of an acoustic filter. The third chapter introduces the near-field imaging technique that can be utilised to directly characterise acoustic surface waves, via spatial fast Fourier transform algorithms of high-resolution pressure field maps. The acoustic response of a square-lattice open-ended hole array is thus characterised. It is found that over a narrow frequency band, the lattice symmetry causes the acoustic surface power flow to be channelled into specific, predictable directions, forming ‘beams’ with a well defined width. In chapter four, the existence of the ‘acoustic line mode’ is demonstrated, a type of acoustic surface wave that may be supported by a simple line of open-ended hole cavities. The near-field imagine technique is again used to extract the mode dispersion. This acoustic line mode may be readily manipulated, demonstrated by arrangement of the line of holes into the shape of a ring. The existence of this type of mode offers a great deal of potential for the control of acoustic energy. Chapter five explores the effect of ‘glide-symmetry’ on a pair of acoustic line modes arranged side-by-side. A control sample not possessing glide- symmetry is first characterised, where measurement of the acoustic near- fields show that this sample supports two separate modes at different frequencies, with their phase either symmetric or anti-symmetric about the mirror plane between the lines of holes. One of these lines is then shifted along its periodicity by half of a grating pitch, thus creating glide-symmetry. The resulting sample is found to support a single hybrid mode, capable of reaching a much larger in-plane wavevector than possible on a simple grating with no gaps in its band-structure, and displaying a region of negative dispersion. The third sample demonstrates how one may increase the coupling strength between the two lines of holes via manipulation of the cavity shape, thus enhancing the glide-symmetry effect. The thesis concludes with preliminary investigations into other possible ways of manipulating acoustic surface waves, such as with the use of ‘screw-symmetry’.

Non-contact manipulation technologies present a useful and powerful means of handling particles or cells. Such techniques are of interest in regenerative medicine applications, and in particular the scalability of these techniques is an area of active research. Optical trapping is a precise and dextrous method of manipulating particles with the forces exerted by a laser beam, while acoustic trapping is a scalable technique capable of exerting a force on particles through standing wave resonance. These complimentary modalities can be utilised in a hybrid system to give a resultant technique that borrows from the strengths of each individual method. In this thesis, methods of force balancing, using optics and acoustics, are explored, both independently and in combination with each other. A technique for 3D acoustic trapping in glass capillaries is shown, utilising the two pairs of opposing channel walls and the air-water interfaces of two air bubbles as acoustic reflectors. Standing waves set up between these surfaces show discrete acoustic trapping sites for varying lengths of fluid cavity. A method of optical radiation force balancing is observed in a 3D potential energy landscape, using similar principles as seen in particle trapping with counter-propagating beams. Tuning of the radiation force balance in this system allows particles to, instead of being pinned to the surface by the radiation force from the optical pattern, become localised at discrete planes of trapping sites throughout the fluid volume. A hybrid force balance separation method using the optical and acoustic forces is devised using a single laser beam as the primary deflection mechanism with acoustic trapping providing both localisation and a force balance with the optics. Separation of different sized particles is observed, with larger scale optical deflection mechanisms and their resultant thermal effects demonstrated.

The purpose of this work was to understand the influence of materials and construction on football performance. Two main areas identified as needing further work were post-impact rebound deviation and acoustic response. To further investigate these areas, football materials were tested in a lab with different loading scenarios and the resulting data was used in various characterisation methods to help define finite element models. The finite element models were used to efficiently explore a variety of material and construction variations. Acoustic data for a range of balls was collected in an anechoic chamber and advanced coupled Eulerian-Lagrangian simulations were developed to visualise the mode shapes of internal resonances.

The need for non-contact micromanipulation methods is apparent for a number of different applications. Optical tweezers, a technique which uses highly focused laser beams to trap and move microscopic objects, has become an important tool for many applications owing to its incredible precision and dexterity. Optical trapping is, however, limited in several ways. It often struggles with particles larger than 10 micrometers, agglomerates and large numbers of particles. Complimentary technologies such as acoustic trapping, aim to overcome some of these limitations. This technique, also termed as Sonotweezers, uses ultrasonic fields to manipulate particles and can manipulate large particles with ease and manipulate large numbers of polydisperse particles and agglomerations, although they currently lack the dexterity of optical tweezers. Combining these two trapping modalities overcomes the some of the limitations of both of them and opens up a new range of useful applications. Three main types of hybrid optical and acoustic traps have been devised and are presented here. The first is an acoustic Bessel beam trap which is used to arrange a large number of polydisperse particles into concentric rings whereupon the smaller particles can then be further manipulated using a single beam optical tweezer. A rudimentary optical sorting system, which pushes particles in a flow laterally using an optical trap, has been combined with an acoustic levitator, which moves all particles away from the edges of the microfluidic channel reducing on sticking and other negative effects. A novel optically transparent ultrasonic device has been developed for easier integration into optical traps without the need for modication. This transparent trap has also been used in combination with a multibeam interference optical sorter to improve the separation between 5 and 10 micron particles.

There is a need for wind sensors with high accuracy and measurement frequency for deployment on the surface of Mars. The wind data obtained to date have been adversely affected by thermal contamination and calibration issues. Improved data would not only help to constrain and validate theoretical models, but also increase safety and longevity of lander operations. The mechanical and thermal wind sensing techniques used on previous missions, whilst sufficient for basic meteorology, are wholly inadequate for measuring fundamental phenomena such as dust and volatile transport. Two promising technologies, optical and acoustic anemometry, could permit precise and high-frequency measurement of three-dimensional wind speeds on the Martian surface. Ultrasonic acoustic anemometry, which relies on time-of-flight measurements, was ultimately chosen for its lower processing requirements and ability to measure the speed of sound; and therefore temperature. Capacitive transducers were selected for their low impedance and high sensitivity, to maximise signal transmission through the rarefied Martian atmosphere. These transducers, which consist of a metallised polymer film oscillating on top of a contoured metal backplane, were evaluated for their suitability as anemometers on the Martian surface. A theoretical framework was assembled to model transducer performance and determine which factors are the most important in determining received signal amplitude. A pair of transducers were designed and manufactured to allow for testing of a wide range of parameters including thickness of the oscillating membrane and diameter. Tests were carried out on the assembled transducers to investigate the dependence on these parameters, and their behaviour was generally found to fit the assembled theoretical framework well. Transducer performance was highly dependent on roughness depth of the backplanes, as expected. The frequency response of the transducers was dominated by the backplane roughness at atmospheric pressure but by film thickness at low pressures. Cross-correlation of the sent and received signals was confirmed as the most reliable signal detection method at low signal amplitudes. The transducers were tested under simulated Martian conditions (a low-pressure carbon dioxide atmosphere with airborne dust), and found to be capable of accurately and reliably measuring the incident wind speed. The cumulative deposition of airborne dust noticeably reduced received signal amplitude, but further testing is required to determine the effect of significant amounts of dust on transducer performance. The impact of the transducer heads impeding the incident fluid flow was found to be very significant in wind tunnel testing. Preliminary computational models were found to accurately predict these effects, but a more comprehensive modelling campaign and experimental validation would be required to ensure accurate instrument calibration.

Complex structures and multiple interfaces of modern microelectronic packages complicate the interpretation of acoustic data. This study has four novel contributions. 1) Contributions to the finite element method. 2) Novel approaches to reduce computational cost. 3) New post processing technologies to interpret the simulation data. 4) Formation of theoretical guidance for acoustic image interpretation. The impact of simulation resolution on the numerical dispersion error and the exploration of quadrilateral infinite boundaries make up the first part of this thesis's contributions. The former focuses on establishing the convergence score of varying resolution densities in the time and spatial domain against a very high fidelity numerical solution. The latter evaluates the configuration of quadrilateral infinite boundaries in comparison against traditional circular infinite boundaries and quadrilateral Perfectly Matched Layers. The second part of this study features the modelling of a flip chip with a 140µm solder bump assembly, which is implemented with a 230MHz virtual raster scanning transducer with a spot size of 17µm. The Virtual Transducer was designed to reduce the total numerical elements from hundreds of millions to hundreds of thousands. Thirdly, two techniques are invented to analyze and evaluate simulated acoustic data: 1) The C-Line plot is a 2D max plot of specific gate interfaces that allows quantitative characterization of acoustic phenomena. 2) The Acoustic Propagation Map, contour maps an overall summary of intra sample wave propagation across the time domain in one image. Lastly, combining all the developments. The physical mechanics of edge effects was studied and verified against experimental data. A direct relationship between transducer spot size and edge effect severity was established. At regions with edge effect, the acoustic pulse interfacing with the solder bump edge is scattered mainly along the horizontal axis. The edge effect did not manifest in solder bump models without Under Bump Metallization (UBM). Measurements found acoustic penetration improvements of up to 44% with the removal of (UBM). Other acoustic mechanisms were also discovered and explored. Defect detection mechanism was investigated by modelling crack propagation in the solder bump assembly. Gradual progression of the crack was found have a predictable influence on the edge effect profile. By exploiting this feature, the progress of crack propagation from experimental data can be interpreted by evaluating the C-Scan image.

This study aimed to understand the processes that govern free surface behaviour in depth-limited turbulent flows. Experimental data has shown that the turbulence properties at a point near the free surface relate directly to the properties of the free surface pattern. This would suggest a direct linkage between the free surface and the underlying turbulence field, but this cannot be true since the free surface pattern is strongly dynamic while the sub-surface turbulence field is relatively persistent. An oscillatory spatial correlation function was derived which explains the de-linkage, showing that the turbulence-generated surface pattern periodically inverts as it advects downstream. A model was developed, which shows that the observed free surfaces can be considered as an ensemble of overlapping but behaviourally independent oscillons. These are shown to influence a zone of fluid beneath the surface and invert at a frequency which is a function of the root-mean-square roughness height of the free surface. The spatial frequency of free surface oscillation relates strongly to the spatial frequency of turbulent structures, suggesting that the oscillon motion may form the trigger for near-bed bursting events. Given these relationships, it is proposed that measurement of the free surface behaviour may allow remote measurement of flow conditions. An acoustic wave probe was developed, which is able to remotely recover the key features of the water surface pattern. An array of such probes is proposed for the accurate measurement of temporal and spatial properties of turbulent free surfaces and hence the underlying bulk flow conditions.

Existing weapon detection systems such as metal detectors and X-ray baggage scanners have many drawbacks. While metal detectors can only detect metallic objects, X-ray scanners are unsafe for use on passengers. Also, these systems can only scan people within a short range. These limitations of detecting potentially harmful objects have led to tragic events such as the 9/11 attack on the world trade centre and the 2008 terrorist attack in Mumbai. Development of more advanced security systems would help in curbing such terrorist attacks. These systems could also be used to help security officials in tackling knife and gun related crimes in the streets. The aim of this research is to develop a concealed weapon detection system using acoustic waves. Ideally, the system would have large standoff distance, should be cost-effective and easy to manufacture and would be able to detect both metal and non-metallic weapons. Different techniques such as acoustic signature, resonance acoustic spectroscopy and acoustic imaging were analysed. Acoustic signature techniques identify the target by comparing the acoustic waves reflected by the target to a database of previously recorded acoustic reflections. Resonance acoustic spectroscopy was used on the data acquired using both experimental measurements and Finite Element simulations. A series of resonant frequencies from the acoustic waves reflected by the concealed target were extracted using this technique. This series of resonant frequencies that are unique to the target were used to identify the target. Acoustic camera was used to experimentally record the acoustic reflection from different targets. This was then used to develop images of concealed targets. These tests were performed using commercially available array speaker systems. The probability of improving these results using a better designed ultrasonic or acoustic array speaker system was analysed. This was done by changing different array design parameters and obtaining a highly focused acoustic beam. The results from the experimental tests and Finite Element simulations proved the possibility of using acoustic waves for concealed weapon detection. In the acoustic signature measurements, the frequency spectra of the reflected acoustic waves were shown to be different for different targets. The results from resonance acoustic spectroscopy showed structural resonant frequencies in the frequency spectra that corresponded to the natural frequency of the target. Using acoustic camera kit the image of the concealed target was identified. The array results showed the formation of focused beams for different array configurations. The results showed the formation of grating lobes and side lobes when the inter-element gap became larger than the wavelength of sound waves at the excitation frequency. Finally, a program using neural network was developed to demonstrate how the natural frequencies from the target could be used to identify them. This research work provides a proof of concept of different acoustic wave-based detection and imaging techniques. It has shown the possibility of detecting concealed targets at standoff distances. Using parametric arrays highly focused acoustic or ultrasonic beams could be generated which could be focused on a person suspected of carrying a weapon in a crowded environment. The sound waves reflected back could be analysed using the resonance acoustic spectroscopic technique or one could use the acoustic camera to generate images of targets in real-time. The use of acoustic waves would also help in keeping the cost and complexity of the equipment to a minimum. It also ensures that the public is not exposed to any harmful radiation. The techniques described in this thesis would significantly support the development of a commercially viable, robust acoustic waves based concealed weapon detection system.

The problem of two-dimensional acoustic scattering of an incident plane wave by a semi-infinite lattice is solved. The problem is first considered for sound-soft cylinders whose size is small compared to the wavelength of the incident field. In this case the formulation leads to a scalar Wiener--Hopf equation, and this in turn is solved via the discrete Wiener--Hopf technique. We then deal with a more complex case which arises either by imposing Neumann boundary condition on the cylinders' surface or by increasing their radii. This gives rise to a matrix Wiener--Hopf equation, and we present a method of solution that does not require the explicit factorisation of the kernel. In both situations, a complete description of the far field is given and a conservation of energy condition is obtained. For certain sets of parameters (`pass bands'), a portion of the incident energy propagates through the lattice in the form of a Bloch wave. For other parameters (`stop bands' or `band gaps'), no such transmission is possible, and all of the incident field energy is reflected away from the lattice.

Ultrasonic instruments are used with the aid of an irrigant such as NaOCl in endodontic treatments to remove dentin debris and calculus from infected root canals. This cleaning process may be assisted by various factors, such as acoustic streaming, and the production of radicals and microjets from the collapse of transient cavitation bubbles. The aim of this project is to understand the principal factors affecting the performance of a number of different endosonic files in order to correlate to their cleaning efficiencies. Characterisation includes detecting transient cavitation activity, mapping the areas of cavitation, assessing the file vibration movements and the streaming effects produced by the files. Experiments to assess the cleaning efficiencies of the files include: emulsification, dye removal with a dental irrigant, ink and hydroxyapatite paste removal from model systems designed to mimic the structure of a tooth. The results show that there is a correlation between the sonochemical output and the cleaning efficiencies, and this brings in further study on the possible factors that may affect the production of transient cavitation and the vibration profiles of the endosonic files. Lastly, a series of computational simulation of the acoustic pressure fields from different endosonic files were performed. Correlations of the simulated and experimental results showed the difference in ultrasonic output of the endosonic files is strongly related to their design. This work provides the basis and techniques necessary to perform a comprehensive study on the design of the endosonic files in order to enhance and optimise their cleaning efficiencies during clinical use and to inform future endodontic practice.

This thesis reports research to investigate the mechanical, thermal and acoustic properties of biodegradable foams in block forms based on wheat starch and developed at Brunel University's School of Engineering & Design, in order to exploit the potential environmental benefits of this renewable and biodegradable class of materials. Two emergent novel technologies have been developed based on a combination of the extrusion foaming of starch in conjunction with the natural adhesive characteristics of moistened starch to produce block foams. Regular Packing & Stacking (RPS), and Compression Bonded Loosefill (CBL), are foam fabrication technologies which have both demonstrated the potential to produce bulk foams based on wheat starch with unique structures and properties - a new class of foam materials in the form of macro-composites reinforced by a network of high-density bonding interfaces. This thesis, as part of a Department of Trade & Industry/Technology Strategy Board funded project, reports an investigation into the following areas to address the scientific and technical issues involved in the further development of the materials and their applications. - The basic properties of the raw materials used in the manufacture of CBL and RPS foams are outlined and the fabrication and preparation of these starch-based foams are described. The limitations of these production techniques are discussed with preliminary work and suggestions made for their enhancement. - Research into the mechanical properties of the CBL and RPS foams includes compression, tensile, creep and dynamic impact tests, whilst the mechanical behaviour of the foams subject to high temperature and high humidity conditions is also reported. - Research into the thermal properties of CBL and high density RPS foams includes testing of the material's thermal conductivity. This aspect of the research also involved a case study detailing the use of RPS in a commercial thermal insulation application. - Research into the acoustic properties of CBL and RPS foams includes tests for sound absorption coefficient and sound transmission loss. - Data obtained from these tests are benchmarked against data pertaining to the mechanical, thermal and acoustic properties of conventional polymer foams in order to provide a basis on which to identify the potential cushioning, thermal insulation and acoustic insulation applications of the starch-based materials. The research has demonstrated the following: - Potential cushioning applications include those limited to the range of static loads within the capabilities of the materials, taking into account the resilience of CBL and RPS which is likely to be compromised by successive impacts. - Tensile forces tend to exploit weaknesses in the macrostructure of these materials. By implication the behaviour of the materials under shear forces would be expected to be similarly compromised. - CBL and RPS exhibited dimensional shrinkage, density increase and significantly reduced mechanical properties under conditions of high temperature and humidity. This suggests that neither CBL nor RPS foams would be suitable for applications in regions where tropical conditions may be encountered unless used in conjunction with other protective materials which would not acutely increase the environmental burden of the products. - Low-density RPS and CBL foams exhibit lower thermal conductivities and hence higher thermal insulation properties compared to many commercially available polymer foams of similar densities. As such these foams have the potential to be used in applications in which a measure of thermal insulation is required. A case study based on an existing commercial application in which the temperature of chilled products must be maintained over a 24 hour period reinforced these findings. - The performance of CBL and RPS starch foams would not provide sufficient functionality to be employed in applications in which dedicated acoustic performance is required, although their sound absorption capabilities may facilitate overall marketability for applications in which a degree of acoustic performance is required if used in conjunction with other materials which demonstrate good acoustic performance. It is anticipated that this work will make significant contributions toward advances in the development of these novel technologies, specifically in terms of establishing an understanding of the properties of the starch-based materials and in identifying potential applications. The research results should thus provide a fundamental element in the basis for the industrial development of these renewable and biodegradable materials.

1. Antarctic krill (Euphausia superba) form aggregations known as swarms that vary greatly in size and density. Six acoustic surveys were conducted as part of multidisciplinary studies at two study sites, the western and eastern core boxes (WCB and ECB), during the 1997, 1998 and 1999 austral summers, at South Georgia. A quantitative, automated, image processing algorithm was used to identify swarms, and calculate swarm descriptors, or metrics. In contrast to acoustic surveys of aggregations of other pelagic species, a strong correlation (r = 0.88, p = 0.02, 95% C.I.= 0.24 to 0.99) between the number of krill swarms and the mean areal krill density [rho.hat] was found. Multivariate analysis was used to partition swarms into three types, based on contrasting morphological and internal krill density parameters. Swarm types were distributed differently between inter-surveys and between on and off-shelf regions. This swarm type variation has implications for krill predators, by causing spatial heterogeneity in swarm detectability, suggesting that for optimal foraging to occur, predators must engage in some sort of adaptive foraging strategy. 2. Krill predator-prey interactions were found to occur at multiple spatial and temporal scales, in a nested, or hierarchical structure. At the largest inter-survey scale, an index of variability, I, was developed to compare variation in survey-scale predator sightings, sea temperature and [rho.hat]. Using I and a two-way ANOVA, core box, rather than year, was found to be a more important factor in determining species distribution. The absence of Blue-petrels (Halobaena caerulea) and the elevated number of Antarctic fur seals (Arctocephalus gazella) suggest that 1998 was a characterised by colder than average water surrounding South Georgia, and a high [rho.hat] in the ECB. At the smaller, intra-survey scales (<80 km, <5 day), the characteristic scale (distances in which predator group size, or krill density were similar, L_s) were determined. For krill and predators L_s varied by survey and the L_s of krill also varied by depth within a survey. Overlap in L_s were stronger between predator species than between a predator species and krill, indicating predators were taking foraging cues from the activity of predators, rather than from the underlying krill distribution. No relationship was found between swarm characteristics and predator activity, suggesting either there is no relationship between krill swarms and predators, or that the predator and acoustic observation techniques may not be appropriate to detect such a relationship. 3. To overcome the 2-D sampling limitations of conventional echosounders, a multibeam echosounder (MBE) observed entire swarms in three-dimensions. Swarms found in the nearshore environment of Livingston Island situated in the South Shetland Islands, exhibited only a narrow range of surface area to volume ratios or roughnesses (R = 3.3, CV = 0.23), suggesting that krill adopt a consistent group behaviour to maintain swarm shape. Generalized additive models (GAM) suggested that the presence of air-breathing predators influenced the shape of a krill swarm (R decreased in the presence of predators: the swarm became more spherical). A 2D distance sampling framework was used to estimate the abundance, N, and associated variance of krill swarms. This technique took into account angular and range detectability (half-normal, [sigma_r.hat] = 365.00 m, CV = 0.16) and determined the vertical distribution of krill swarms to be best approximated by a beta-distribution ([alpha.hat] = 2.62, [CV.hat] = 0.19; [beta.hat] = 2.41, [CV.hat] = 0.15), giving the abundance of swarms in survey region as [N.hat] = 5,062 ([CV.hat] = 0.35). This research represents a substantial contribution to developing estimation of pelagic biomass using MBEs. 4. When using a single- or split-beam missing pings occur when the transmit or receive cycles are interrupted, often by aeration of the water column, under the echosounder transducer during rough weather. A thin-plate regression spline based approach was used to model the missing krill data, with knots chosen using a branch and bound algorithm. This method performs well for acoustic observations of krill swarms where data are tightly clustered and change rapidly. For these data the technique outperformed the standard MGCV GAM, and the technique is applicable for estimating acoustically derived biomass from line transect surveys.

The work presented in this thesis forms part of a research project which attempts to generate a visualisation of a speaker's mouth from purely acoustic speech signals. The aim is to provide an aid for partially hearing impaired people in which visual information is presented alongside limited acoustic signals, facilitating easier use of the telephone. The system is essentially a low-level speech recogniser in which phonemic information is extracted from the speech waveform and mapped onto visemes generated on a synthetic facial image. This thesis presents a description of a major part of this project, that is, the development of an accurate phoneme discriminator which is capable of speaker independent operation, on continuous speech. The recognition process is realised in three stages: a pre-processor to convert the speech into a suitable parametric form; a pattern recogniser to identify the possible phoneme classes and a post-processor to produce the viseme information. The pattern recognition stage uses a self-organising Kohonen network, followed by a Learning Vector Quantiser (LVQ) to further improve the recognition accuracy. The performance of this stage is highly dependent on the choice of pre-processor used at the input to the network and it is the design of the pre-processor stage that forms a significant part of this work. A novel technique known as the pseudo-cepstrum forms the basis of this pre-processor. Extensive investigations have been conducted into the dependence of performance on a range of parameters, both at the pre-processor stage and within the Kohonen classifier. In particular, a performance comparison of several preprocessor techniques, including the pseudo-cepstrum, has been carried out. Factors affecting both the training and operation of the classifier are also described here, with the sensitivity of recognition performance to the input data, being a major issue. Overall recognition accuracies of 80% have been achieved.