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The aim of this investigation was to make a flexible array of pulse-echo ultrasound transducers by etching two orthogonal linear arrays of conducting elements into the metallisation of either side of a sheet of PVdF. These would then be multiplexed under computer control in an X-Y raster, thereby forming an image of subsurface defects in a material specimen. A potential source model was used to predict the sensitivity of a single element air-backed transducer far from resonance. Initial investigations confirmed the predictions, and reaffirmed the results of previous workers. In making a prototype array, it was found necessary to use a bi-laminar arrangement with a central ground plane, due to difficulties with crosstalk and charge leakage into the specimen materials. The radiation pattern of this array was tested and found to agree with the predictions for Fraunhofer (Far-Field) radiation. A 10 MHz analogue to digital converter was constructed to interface with the IBM-PC clone as a transient recorder, through a data capture program written in 'C'. However, the electrical noise generated by the PC was found to interfere strongly with the signal from the array transducer. A wide-band amplifier and full-wave rectifier was then added to the multiplexer and A/D converter, and the system enclosed in an electrically isolated environment, which made it possible to obtain clear signal data from the transducer. Non-linear regression was implemented in the software, to smooth the data and locate echo peaks, and the most frequently occurring peak separation was used to indicate sample thickness at that location in a false-colour mapping on the screen of the PC.

Eigen-mode matching techniques offer a versatile approach for solving acoustic scattering problems in ducts. However, until recently, these techniques have been restricted to problems in which the boundary conditions contain at most one derivative, that is, Neumann, Dirichlet or Robin's conditions. Here a method is developed to solve scattering problems in ducts that are discontinuous in height and have at least one surface described by a high order boundary condition. Attention is focussed on the membrane condition, but the method can be extended to elastic plates and other higher order conditions. An original orthogonality condition is derived and used to solve two problems. Limiting cases of the results are compared with some special cases solveable by standard Fourier techniques and (for the case of no height discontinuity) the Wiener-Hopf technique.

Time resolved pressure measurements in hydropower applications are of great interest. Different parts of the machine experience highly transient flows that influence the function and efficiency of the turbine. This thesis addresses different time dependent pressure phenomena. Assessment of the efficiency of a hydropower plant requires accurate flow measurements. Gibson's method is a pressure time based method to measure the flow rate. To improve the method outside its standard range an experimental investigation is performed in a laboratory setup in parallel with numerical solutions of the governing equations. The results indicate that it is possible to correct the flow measurements outside the limitations of the standard. A draft tube is an integrated part of a hydropower plant with a reaction turbine where the remaining kinetic energy of the flow after the turbine is converted into pressure. An experimental investigation is performed on a model hydropower draft tube at Älvkarleby to establish the details of the pressure recovery in the early part of the draft tube. The objective is to increase the understanding of the pressure behaviour and to contribute with data for CFD (Computational Fluid Dynamics) validations. The results show a high damping of the oscillating parts of the pressure in the axial direction. From earlier investigations done as part of the Turbine-99 workshops, it has been observed that the radial pressure distribution just under the turbine runner show a marked discrepancy between experiments and CFD. The flow in the region is highly time dependent so the behaviour of the Pitot tube used for the pressure measurements is investigated for oscillating flow in a lab setup. A method to derive more accurate data is proposed. / <p>Godkänd; 2006; 20070109 (haneit)</p>

The utilization of rivers for hydropower production leads to problems for fish migration. Migratory fish that swim upstream for reproduction need to overcome obstructions to reach their spawning grounds. On their way upstream they follow high water velocities. Since most of the water in regulated rivers flow through the power plants the fish is often attracted to the turbine outlets. To guide the fish past the power plants, fishways are often used. However the efficiency is often low due to inefficient attraction water. An attraction channel that uses a small fraction of the tailwater, or any free stream, is studied. The channel is open and U-shaped. A local acceleration of the water is created by changing the cross sectional area in the downstream end of the channel. The flow in the channel is measured with LDV in a lab setup to examine the acceleration of the water, and in full-scale to investigate the fish tendency to use the channel. The results show that the velocity out of the channel can be as much as 38 % higher than the approaching flow. The acceleration is detectable downstream the channel up to 18 times the exit water depth of the channel. The results from the field work shows that fish do use the channel and it is important that it is painted dark. / <p>Godkänd; 2006; 20070109 (haneit)</p>

Recent studies have shown that nanoparticles may be more toxic than larger particles of the same material, but the health risks associated with widespread use largely depend on the extent of exposure. When dealing with potentially toxic particles, precautionary measures have to be taken in order to minimize contact. For larger particles, mechanical filtering is commonly used. Nanoparticles, however, are too small to be effectively impeded by these filters and thus alternative methods need to be developed. Experiments are performed where clusters of carbon nanotubes are dropped vertically into a region with an electric field, generated between two parallel plates. The clusters are strongly affected by the field and move swiftly towards the electrodes. In this setup, most clusters simply bounce between the electrodes. By adding an electrically insulating layer to one of the plates, however, the particles get stuck. This implies that electrostatic filtration is an effective means of collecting airborne carbon nanotubes. Nanoparticles may enter human lung regardless if filtration is used or not. To examine the health risks, therefore, knowledge of transport and deposition properties of aerosol particles in lung flows is necessary. This information is also essential in the optimization of targeted drug delivery with pharmaceutical aerosols. In vivo and in vitro studies are cost-intensive and difficult to perform for studying particle deposition in the airways. Hence, numerical simulations constitute a valuable complement. The extent and location of particle deposition depend on particle properties, airway geometry and breathing pattern. To start with, Computational Fluid Dynamics simulations are performed for spherical particles, 15 nanometer to 50 micrometer in diameter, in a multiply bifurcated asymmetric 3D model, representing trachea to the segmental bronchi. Steady, laminar flow is considered for inhalation flow rates of 0.1 and 0.5 l/s. The largest particles are captured near the first bifurcation, whereas smaller microparticles are less efficiently, but more uniformly, deposited. The site of deposition is also affected by geometric asymmetry. The nanoparticles essentially follow the streamlines and travel unaffected through the region modeled. Thus, transport to the distal airways can be assumed extensive. Because of their specific shape, fibers may cause additional harm compared to spherical particles. Asbestos is a well-known example of hazardous fibrous materials. More recently, this has also called for concern on the extended use of nanotubes. A numerical model is developed for fiber transport in the respiratory airways. The coupled equations for fiber rotation and translation are solved using MATLAB. The model is valid for arbitrary Stokes flows at low particle concentrations and for particle sizes from nano- to the micro range. The results suggest that the potential of a fiber to reach the distal airways increases with increased fiber aspect ratio, regardless of particle size. / <p>Godkänd; 2008; 20080428 (ysko)</p>

Cellulose material is processed to pulp suspensions and MDF boards in order to produce products such as papers, magazines, laminate floors or door skins. A critical stage of these processes is when the cellulose fiber networks are compressed to specific densities and when most of the fluid originally positioned between and inside the fibers is forced to leave the network. The fiber network is then exposed to a drag force generated by the flow. The magnitude of this force is dependent upon how easy the fluid can flow through the network, which is commonly described by its permeability. In addition to the permeability, which relates to the drag on each fiber, there is a solid network force. The response to this force from the fiber network is often termed as the compressibility of it. Hence, to be able to model and predict the compression stage in cellulose material related processes these two material properties must be known. In this thesis two equipments to measure the permeability of MDF networks and pulp suspensions are evaluated and a neat model for a part of the MDF- compression stage is developed. A reference material consisting of spherical particles and relevant fiber networks are used as test objects for the equipments enabling a comparison to theoretical models and existing experimental results. The outcome is that correct enough permeability data are obtained with respective equipment as long as Reynolds number is sufficiently low. The equipments are then used to study different materials showing, for instance, that highly compressed MDF-networks are strongly anisotropic as to permeability and that the tested hardwood pulps have an overall higher permeability compared to the softwood pulps investigated. It was also found that the permeability of the pulps was not influenced by different mechanical treatments of the fiber network, as long as the geometrical dimensions of the fibers were constants. / <p>Godkänd; 2006; 20070109 (haneit)</p>

Spectrograms are perhaps the most commonly used method for studying the characteristics of speech waveforms. Producing a spectrogram can conveniently be divided into two parts, the analysis and the display, and this thesis describes a study of both these aspects.

Room modes are a recognised problem in small critical listening rooms and are known to cause colouration of sound reproduced within them. Investigations on the causes and solutions for this problem have been carried out for some time. Interest in the topic has extended to loudspeaker manufacturers who have mainly concentrated in developing methods for controlling the loudspeaker-room interaction in order to ameliorate low frequency reproduction. Compared to objective work on passive and active control methods, the study of the subjective perception of room resonances has been somewhat neglected. Available publications mostly concern the effects of single resonances, which are perhaps not fully representative of conditions as experienced in real rooms. A study into the subjective perception of room modes is presented. The experimental methodology employs psychoacoustic techniques to study the perception of factors such as modal distribution, and effects of resonances on single tones. Results show that the subjective perception of room modes is strongly affected by temporal issues, and that changes exerted merely on magnitude frequency response are detectable but not likely to remove the effects of resonances for all listeners. Furthermore, it is shown that a reduction of the modal Q-factor, associated with a reduction of decay rates, has a significant effect in decreasing the detection of resonances. Q-factor difference limen were evaluated for three reference decay characteristics corresponding to reference Q-factors of 30, 10 and 1. The limen were 6±2.8, 10±4.1 and 16±5.4 respectively, meaning that detection of changes to modal decay decreases with decreasing decay time. These results may be used to define more perceptually relevant design guidelines for critical listening environments, and indicate target criteria for control techniques used in room correction. The outcomes of this investigation will have repercussions on the design of better rooms for critical listening.

<p> The objective of this dissertation is the design, development, and experimental evaluation of novel algorithms and reconfigurable radio architectures for spectrally efficient cognitive networking in terrestrial, airborne, and underwater environments. Next-generation wireless communication architectures and networking protocols that maximize spectrum utilization efficiency in congested/contested or low-spectral availability (extreme) communication environments can enable a rich body of applications with unprecedented societal impact. In recent years, underwater wireless networks have attracted significant attention for military and commercial applications including oceanographic data collection, disaster prevention, tactical surveillance, offshore exploration, and pollution monitoring. Unmanned aerial systems that are autonomously networked and fully mobile can assist humans in extreme or difficult-to-reach environments and provide cost-effective wireless connectivity for devices without infrastructure coverage. </p><p> Cognitive radio (CR) has emerged as a promising technology to maximize spectral efficiency in dynamically changing communication environments by adaptively reconfiguring radio communication parameters. At the same time, the fast developing technology of software-defined radio (SDR) platforms has enabled hardware realization of cognitive radio algorithms for opportunistic spectrum access. However, existing algorithmic designs and protocols for shared spectrum access do not effectively capture the interdependencies between radio parameters at the physical (PHY), medium-access control (MAC), and network (NET) layers of the network protocol stack. In addition, existing off-the-shelf radio platforms and SDR programmable architectures are far from fulfilling runtime adaptation and reconfiguration across PHY, MAC, and NET layers. Spectrum allocation in cognitive networks with multi-hop communication requirements depends on the location, network traffic load, and interference profile at each network node. As a result, the development and implementation of algorithms and cross-layer reconfigurable radio platforms that can jointly treat space, time, and frequency as a unified resource to be dynamically optimized according to inter- and intra-network interference constraints is of fundamental importance. </p><p> In the next chapters, we present novel algorithmic and software/hardware implementation developments toward the deployment of spectrally efficient terrestrial, airborne, and underwater wireless networks. In Chapter 1 we review the state-of-art in commercially available SDR platforms, describe their software and hardware capabilities, and classify them based on their ability to enable rapid prototyping and advance experimental research in wireless networks. Chapter 2 discusses system design and implementation details toward real-time evaluation of a software-radio platform for all-spectrum cognitive channelization in the presence of narrowband or wideband primary stations. All-spectrum channelization is achieved by designing maximum signal-to-interference-plus-noise ratio (SINR) waveforms that span the whole continuum of the device-accessible spectrum, while satisfying peak power and interference temperature (IT) constraints for the secondary and primary users, respectively. In Chapter 3, we introduce the concept of all-spectrum channelization based on max-SINR optimized sparse-binary waveforms, we propose optimal and suboptimal waveform design algorithms, and evaluate their SINR and bit-error-rate (BER) performance in an SDR testbed. Chapter 4 considers the problem of channel estimation with minimal pilot signaling in multi-cell multi-user multi-input multi-output (MIMO) systems with very large antenna arrays at the base station, and proposes a least-squares (LS)-type algorithm that iteratively extracts channel and data estimates from a short record of data measurements. Our algorithmic developments toward spectrally-efficient cognitive networking through joint optimization of channel access code-waveforms and routes in a multi-hop network are described in Chapter 5. Algorithmic designs are software optimized on heterogeneous multi-core general-purpose processor (GPP)-based SDR architectures by leveraging a novel software-radio framework that offers self-optimization and real-time adaptation capabilities at the PHY, MAC, and NET layers of the network protocol stack. Our system design approach is experimentally validated under realistic conditions in a large-scale hybrid ground-air testbed deployment. Chapter 6 reviews the state-of-art in software and hardware platforms for underwater wireless networking and proposes a software-defined acoustic modem prototype that enables (i) cognitive reconfiguration of PHY/MAC parameters, and (ii) cross-technology communication adaptation. The proposed modem design is evaluated in terms of effective communication data rate in both water tank and lake testbed setups. In Chapter 7, we present a novel receiver configuration for code-waveform-based multiple-access underwater communications. The proposed receiver is fully reconfigurable and executes (i) all-spectrum cognitive channelization, and (ii) combined synchronization, channel estimation, and demodulation. Experimental evaluation in terms of SINR and BER show that all-spectrum channelization is a powerful proposition for underwater communications. At the same time, the proposed receiver design can significantly enhance bandwidth utilization. Finally, in Chapter 8, we focus on challenging practical issues that arise in underwater acoustic sensor network setups where co-located multi-antenna sensor deployment is not feasible due to power, computation, and hardware limitations, and design, implement, and evaluate an underwater receiver structure that accounts for multiple carrier frequency and timing offsets in virtual (distributed) MIMO underwater systems.</p><p>