Doctoral

Development of Novel Fiber Optic Humidity Sensors and Their Derived Applications

Jinesh Mathew — Tue, 12 Mar 2013 02:55:07 PDT

The main focus of this thesis is on the design and development of novel fiber optic devices for relative humidity (RH) sensing with emphasis on high sensitivity, a wide humidity range, low temperature dependence, fast response time and good stability.
Novel RH sensors based on fiber bends are fabricated by coating the surface of the buffer stripped bent fiber with selected hygroscopic materials such as Polyethylene oxide or Agarose. It is shown that the Polyethylene oxide coated device has a high sensitivity in a narrow RH range while the Agarose coated fiber bend shows a linear RH sensitivity in a wide RH range. Both of these sensors demonstrate a fast response (in the order of milliseconds) to RH variations. The limitations of fiber bend based humidity sensors are also discussed in the thesis. A novel RH sensor based on a reflection type photonic crystal fiber interferometer (PCFI) is presented which does not rely on the use of any hygroscopic material. The operating principle of a PCFI sensor based on the adsorption and desorption of water vapour at the silica-air interface within the PCF capillaries is discussed. The demonstrated sensor shows a good RH sensitivity in the higher RH range. Furthermore this RH sensor is almost temperature independent and can also be used in a high temperature and high pressure environment for humidity sensing.
In order to improve the sensitivity of a reflection type PCFI over a wider RH range an alternative sensor is developed by infiltrating the microholes of the PCF with the hygroscopic material Agarose. The demonstrated novel sensor has a good sensitivity, a fast response time and a compact size. The temperature dependence of the device is also investigated. A novel hybrid device based on Agarose infiltrated PCFI interacting with a fiber Bragg grating is also presented which can simultaneously measure RH and temperature.
A novel RH sensor based on a transmission type photonic crystal fiber interferometer coated with Agarose is also presented and discussed. This structure is used to study the effect of Agarose coating thickness in such a sensor on the RH sensitivity. It is demonstrated that the RH sensitivity of the sensor has a significant dependence on the thickness of the coating. An experimental method is also demonstrated to select an optimum coating thickness to achieve the highest sensitivity for a given RH sensing range. The sensor with the highest demonstrated sensitivity shows a linear response in the RH ranges of 40-80 % and 80-95 % with a sensitivity of 0.57 nm/%RH and 1.43 nm/%RH respectively.
Finally, a comparison of the four RH sensing devices is presented, based on their size, operating range, RH sensitivity, temperature dependence and response time, in the context of selecting suitable devices for end-user applications. Two examples of applications are presented: dew sensing and breathing monitoring. The reflection type PCFI which does not use any hygroscopic material is selected for dew sensing and the dew response of the device is presented and discussed. Finally a novel breathing sensor based on the Agarose infiltrated PCFI is developed, which due to its immunity to interference from electric and magnetic fields, is suitable for breath monitoring of patients during medical procedures such as a magnetic resonance imaging scan.

Power Quality Improvement of Distributed Generation Integrated Network with Unified Power Quality Conditioner.

Shafiuzzaman Khan Khadem — Wed, 06 Mar 2013 07:52:45 PST

With the increased penetration of small scale renewable energy sources in the electrical distribution network, maintenance or improvement of power quality has become more critical than ever where the level of voltage and current harmonics or disturbances can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution for enhancing the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objective of the present research is to investigate the (i) placement (ii) integration (iii) capacity enhancement and (iv) real time control of the Unified Power Quality Conditioner (UPQC) to improve the power quality (PQ) of a distributed generation (DG) network connected to the grid or microgrid.

Monitoring and Regression Based Modelling of End Winding Vibration in Large Synchronous Generators

David Shally [Thesis] — Tue, 12 Feb 2013 05:26:44 PST

This research project was set up to monitor, on an ongoing basis, the condition of the end windings and their support structures of a 288 MVA 2-pole synchronous generator with a known end winding vibration problem
Excessive vibration at the end windings was caused by the natural frequencies of individual end bars (local) and of the entire end winding structure (global) being at or close to the magnetic forcing frequency of 100 Hz. Resonant vibration such as this has been a cause of major failures in machines of the same type in the past, resulting in significant down time ranging from a few weeks to a number of months, with the obvious implications in terms of cost, generator availability and revenue loss.
The project covers the installation of an end winding vibration monitoring system, subsequent analysis and testing in order to attempt to lower peak vibration levels, a low tune modification of the end winding support structure (carried out by the OEM) in order to remedy the natural frequency issue, subsequent data analysis and development of regression models to allow the prediction of vibration levels based on plant data and the implementation of the models on PI ACE (Advance Computing Engine). A webpage, available to all plant personnel via the company intranet was then created to display the actual measured vibration data against the model predicted values and other relevant plant data.
With the issue of excessive vibration due to resonance having been remedied by the Original Equipment Manufacturer (OEM) the focus of the project shifted somewhat towards providing an easily interpreted, easily accessible method of monitoring the condition of a now relatively healthy machine well beyond the conclusion of this project. The development of the regression models and web page was seen as the best way of achieving this.

Reducing Life Cycle Impacts of the Existing Irish Housing Stock.

Albert A. Famuyibo — Mon, 11 Feb 2013 08:37:58 PST

Abstract

Despite the importance of addressing the challenges of the 2020 emissions reduction targets of both the European Union (EU) and Ireland, current residential emissions policies have focused mainly on the few existing studies that are primarily used to predict end-use energy and CO₂ emissions savings. To allow all energy and emissions across life cycle phases to be evaluated, a process-based life cycle analysis (LCA) hybrid model was developed with the aim of determining the extent of reductions in resource consumption, greenhouse gas (GHG) emissions and costs of maintaining the existing Irish housing stock.

Thirteen representative archetypes of the pre-1960 – 2002 existing housing stock were developed, and the impacts of each archetype assessed across life cycle phases to give a ‘BaseCase’ for energy and emissions. Two scenarios for upgrading the housing stock model were analysed – ‘meet current building regulations’ (Building Regulations standard) and 'meet anticipated future regulations' (Passive House standard i.e. a house that has its operational energy demand as low as practically achievable). This involved identifying and modelling a range of interventions which achieved energy ratings equivalent to the Irish 2010 building regulations and Passive House standards, respectively. These upgraded stock models were then reassessed to estimate their impacts on energy and emissions. Cost evaluations were also carried out for the differing archetype upgrades.

For all archetypes in the BaseCase scenario, results show that operational phase energy and emissions are much greater than for any other phase, representing at least 95.5% in a majority of archetypes. 13% of the life cycle’s energy consumption was estimated to come from non-Irish sources. For a majority of archetypes, the weighted average archetype embodied energy was estimated to be approximately 0.5% of the life cycle energy out of which 29% was estimated as embodied energy due to services (i.e. installation of materials and fit-outs). All retrofit scenarios yield significant operational improvement: primary energy reduced for a majority of dwellings, compared to the BaseCase scenario.

It is estimated that a total of 76MtCO₂-eq and 104.2MtCO₂-eq national life cycle emissions savings compared to 2005 levels can be achieved at positive retrofitting abatement costs of €592/tCO₂-eq and €741/tCO₂-eq in 2020 for the Current Regulations and Passive House scenarios, respectively. A comparison between Current regulations and Passive House scenarios indicated that a total of 21.2MtCO₂-eq national emissions savings compared to 2005 levels can be achieved at retrofitting abatement costs of €1,141/tCO₂-eq in 2020. Detached houses in the Passive House scenario in year 2020 is a good choice for energy efficiency improvement as they represent the highest GHG abatement potential that can be delivered at relatively lowest costs, especially when it is considered that they become more cost effective overtime. This is followed by mid-terraced houses/apartments. Semi-detached houses/end-terraced houses display the lowest GHG abatement at highest retrofitting costs. The effective implementation of this choice will require a combination of regulation, financial support and information/education.

The Characterisation and Numerical Modelling of Viscoelastic Polyurethane Foams for use in Custom Wheelchair Seating.

Conor Briody — Fri, 08 Feb 2013 04:40:40 PST

Viscoelastic polyurethane foam is widely used in wheelchair cushions as it offers good pressure relieving capabilities. However, the behaviour of this material is largely un-quantified, by comparison with conventional elastomeric materials. Consequently, in many cases, inadequate cushioning is provided to wheelchair users with complex seating requirements. This thesis characterises and numerically models viscoelastic polyurethane foam. Temperature-dependent static compression and simple shear test procedures are conducted on a range of viscoelastic polyurethane foams and selected results are utilised to identify Ogden Hyperfoam material model parameters. Time-dependent creep and stress relaxation test procedures are conducted and test results are used in conjunction with Time-Temperature-Superposition (TTS), William-Landel- Ferry (WLF) and Arrhenius theories to generate long-term predictions of material behaviour. Appropriate spring-dashpot models are utilised to model predicted long-term viscoelastic performance. Thermal conductivity parameters are obtained using Glicksman’s theoretical model. The accuracy of predictions obtained using TTS and WLF theories has been proven. Validation has also been achieved for the temperature-dependent Hyperfoam, long-term viscoelastic and thermal conductivity parameters. The range of fully validated material model parameters were utilised to simulate the in-service seating behaviour of polyurethane foam. Simulation results were relatively compared and analysed with respect to relevant pressure ulcer risk factors. From analyses of the FE simulations, results lend support to findings from clinical trials particularly with respect to the relationship between shear and direct pressure in wheelchair seating. Other FE results disagree with accepted seat prescription timings used in current clinical practises.

Arterial Tissue Perforation Using Ultrasonically Vibrating Wire Waveguides

Mark Wylie — Fri, 23 Nov 2012 08:16:09 PST

Chronic Total Occlusions (CTOs) are fibrous and calcified atherosclerotic lesions which completely occlude the artery. They are difficult to treat with standard dilation procedures as they cannot be traversed easily. Their treatment is also associated with a high risk of arterial perforation. Low frequency ultrasonic vibrations delivered via wire waveguides represent a minimally invasive treatment for CTOs and other tissue ablation applications. These devices typically operate at 20–50 kHz delivering wire waveguide distal tip amplitudes of vibration of 0-60 μm. The diseased tissue is ablated or disrupted by repetitive direct mechanical contact and cavitation. This research assesses the susceptibility of arterial tissue to perforation and residual damage under the action of ultrasonically energised wire waveguides. Using Finite Element Analysis (FEA), a linear acoustic model of the wire waveguide distal tips can predict the pressures for a range of operating parameters typically used for these devices. High mesh densities (140 EPW) were required to solve the entire acoustic field, including complex wave interactions. The FEA model was used to aid in the further design and modification of an ultrasonic apparatus and wire waveguide (0–34.3 μm at 22.5 kHz). Using a test rig, the effects of distal tip amplitudes of vibration, feedrate and angled entry on the perforation forces, energy and temperature were measured. The perforation forces reduced (≈ 60%, 6.13 N - 2.46 N mean) when the wire waveguide was energised at low amplitudes of vibrations (< 27.8 μm). There were no significant change in tissue perforation forces above this or when the waveguide was operating above the cavitation threshold. Histological analysis also showed tissue removal. While this knowledge is useful in the prediction and avoidance of perforations during CTO operations; it is also envisaged that this information can aid in the design and development of generic ultrasonic wire waveguide tissue cutting tools.

Using Virtual Reality Modelling to Enhance Electrical Safety and Design in the Built Environment.

Martin Barrett — Wed, 03 Oct 2012 02:16:48 PDT

This thesis presents a prototype desktop virtual reality model entitled ‘Virtual Electrical Services’, to enhance electrical safety and design in the built environment. The model presented has the potential to be used as an educational tool for third level students, a design tool for industry, or as a virtual electrical safety manual for the general public. A description of the development of the virtual reality model is presented along with the applications that were developed within the model. As part of the VR development process, this research investigates the cause and effects of electrical accidents in domestic properties. This highlights the high-risk activities, which lead to receiving an electric shock in a domestic property and identifies at-risk groups that could most benefit from electrical safety interventions. It also examines the theory of transfer touch voltage calculations and expands on it to show how to carry out a sensitivity analysis in relation to the design parameters that are being used by designers and installers. The use of Desktop Virtual Reality systems for enhancing electrical safety and engineering design is a novel prospect for both practicing and student electrical services engineers. This innovative approach, which can be readily accessed via the World Wide Web, constitutes a marked shift in conventional learning and design techniques to a more immersive, interactive and intuitive working and learning environment. A case study is carried out to evaluate the users’ attitudes toward VR learning environments and also the usability of the prototype model developed. From the completed case study, it appears that there is sufficient evidence to suggest that virtual reality could enhance electrical safety and design in the built environment and also advance training methods used to educate electrical services engineers and electricians. The thesis includes a discussion on the limitations of the system developed and the potential for future research and development

Phase-Distortion-Robust Voice-Source Analysis

Alan O Cinneide (Thesis) — Mon, 10 Sep 2012 05:15:34 PDT

This work concerns itself with the analysis of voiced speech signals, in particular the analysis of the glottal source signal. Following the source-filter theory of speech, the glottal signal is produced by the vibratory behaviour of the vocal folds and is modulated by the resonances of the vocal tract and radiation characteristic of the lips to form the speech signal. As it is thought that the glottal source signal contributes much of the non-linguistic and prosodical information to speech, it is useful to develop techniques which can estimate and parameterise this signal accurately. Because of vocal tract modulation, estimating the glottal source waveform from the speech signal is a blind deconvolution problem which necessarily makes assumptions about the characteristics of both the glottal source and vocal tract. A common assumption is that the glottal signal and/or vocal tract can be approximated by a parametric model. Other assumptions include the causality of the speech signal: the vocal tract is assumed to be a minimum phase system while the glottal source is assumed to exhibit mixed phase characteristics. However, as the literature review within this thesis will show, the error criteria utilised to determine the parameters are not robust to the conditions under which the speech signal is recorded, and are particularly degraded in the common scenario where low frequency phase distortion is introduced. Those that are robust to this type of distortion are not well suited to the analysis of real-world signals. This research proposes a voice-source estimation and parameterisation technique, called the Power-spectrum-based determination of the Rd parameter (PowRd) method. Illustrated by theory and demonstrated by experiment, the new technique is robust to the time placement of the analysis frame and phase issues that are generally encountered during recording. The method assumes that the derivative glottal flow signal is approximated by the transformed Liljencrants-Fant model and that the vocal tract can be represented by an all-pole filter. Unlike many existing glottal source estimation methods, the PowRd method employs a new error criterion to optimise the parameters which is also suitable to determine the optimal vocal-tract filter order. In addition to the issue of glottal source parameterisation, nonlinear phase recording conditions can also adversely affect the results of other speech processing tasks such as the estimation of the instant of glottal closure. In this thesis, a new glottal closing instant estimation algorithm is proposed which incorporates elements from the state-of-the-art techniques and is specifically designed for operation upon speech recorded under nonlinear phase conditions. The new method, called the Fundamental RESidual Search or FRESS algorithm, is shown to estimate the glottal closing instant of voiced speech with superior precision and comparable accuracy as other existing methods over a large database of real speech signals under real and simulated recording conditions. An application of the proposed glottal source parameterisation method and glottal closing instant detection algorithm is a system which can analyse and re-synthesise voiced speech signals. This thesis describes perceptual experiments which show that, iunder linear and nonlinear recording conditions, the system produces synthetic speech which is generally preferred to speech synthesised based upon a state-of-the-art timedomain- based parameterisation technique. In sum, this work represents a movement towards flexible and robust voice-source analysis, with potential for a wide range of applications including speech analysis, modification and synthesis.

A Study of Integrated UWB Antennas Optimised for Time Domain Performance

Antoine Dumoulin (Thesis) — Mon, 10 Sep 2012 05:15:32 PDT

Antennas for impulse radio ultra-wideband based portable devices are required to be compact and able to transmit or receive waveforms with minimal distortion in order to support proximity ranging with a centimetre-scale precision. The first part of thesis characterises several pulse types for use in the generation of picosecond-scale signals in respect to the regulatory power and frequency standards while the principles of antenna transient transmission and reception are stated. The proximity effect of planar conductors on the performance of an ultra-wideband antenna is investigated in both spectral and temporal domain demonstrating the relationship between the antenna-reflector separation and the antenna performance. Balanced and unbalanced antennas are also investigated for integration into asset-tracking tag applications and are designed to operate in close proximity to PCB boards while meeting realistic dimensional constraints and acceptable time domain performances. Monopole antenna designs are reported with performances optimized for minimum pulse dispersion. Minimization of pulse dispersion effects in the antenna designs is achieved using pulses with optimal spectral fit to the UWB emission mask. The generation of these waveforms are reported for the first time. An antenna de-embedding method is reported enabling validation of the simulated fidelity factor of radiated patterns. Novel differentially-fed planar dipole and slot antennas are reported for direct IC output integration. Design objectives and optimisation are focused on bandwidth enhancement and pulse dispersion minimisation. Finally, time- and frequency-domain measurements are carried out using an approach based on the superposition principle.

A Novel QoS-Aware MPEG-4 Video Delivery Algorithm over the Lossy IEEE 802.11 WLANs to Improve the Video Quality

Tanmoy Debnath (Thesis) — Thu, 16 Feb 2012 01:24:31 PST

Video traffic is bursty in nature and has different network requirements compared to other types of traffic (e.g. voice, data) in terms of bandwidth, delay, jitter, and loss etc. So it becomes important to manage video traffic on a WLAN carefully to achieve acceptable levels of Quality of Service (QoS). The unique contribution of this work is that it presents experimental and simulation studies of the performance of real video content streamed over WLAN networks. Under various test scenarios the performance of the WLAN network in terms of delay, loss, throughput etc. is analysed in the presence of background traffic. The effects of different types of server configurations and access contention between stations are also investigated for IEEE 802.11b and IEEE 802.11e networks. This work specifically considers the IPB fame based nature of MPEG- 4 encoded video. A novel QoS aware MPEG-4 video delivery algorithm is proposed and evaluated using a computer model written in the C programming language. The model exploits two mechanisms namely frame retransmission (ReTx) and GOP truncation (GOPT). The ReTx mechanism effectively increases the QoS by minimising the transmission losses at the expense of an increased buffer overflow probability. The GOPT mechanism reduces the probability of buffer overflow at the expense of a reduced QoS. The QoS aware MPEG-4 video delivery algorithm aims to achieve an optimal trade off between these two mechanisms in order to eliminate buffer overflow and minimise transmission losses. The algorithm aims to replace uncontrolled packet loss due to buffer overflow, MAC collisions, and transmission errors by a controlled prioritized packet loss scheme that permits a graceful degradation in MPEG-4 video quality streamed over IEEE 802.11b networks. This ensures the realisation of the most favourable network conditions for the delivery of MPEG-4 video frames on WLANs. Through extensive simulations it has been shown to provide a significant improvement in the QoS performance for video streaming applications for both uplink and downlink network scenarios in the presence of background traffic.

Novel Approaches to the Analysis of Localised Stress Concentrations in Deformed Elastomers

John McNamara (Thesis) — Wed, 15 Feb 2012 07:39:45 PST

The research described here is concerned with improving finite element analysis (FEA) of rubber components subjected to dynamic loading, particularly in respect of accurate modelling of stress softening using standard software codes and phenomenological material models. The research required the design and implementation of a user subroutine capable of inclusion in standard highly nonlinear codes. Experimental methods were employed to corroborate the FEA simulations and so validate the subroutine. This was also achieved using 3D image correlation photogrammetry (ICP) and other novel experimental procedures. From this experimentation and modelling, the results for different rubber specimens and load cases were presented. The primary aim of the research was to provide a novel method for modelling stress softening for localised stress concentration at discontinuities in rubber components and to implement optimised stress softening subroutines for rubber into commercial software codes. As a consequence other novel research is presented in respect of: i) A semi empirical formula for elastomer stress softening. ii) Recommendations for improving ICP techniques applied to rubber. iii) A determination of the likelihood of large flaws causing premature failures in rubber specimens.

A Methodology Towards Comprehensive Evaluation of Shape Memory Alloy Actuators for Prosthetic Finger Design

Kevin O'Toole (Thesis) — Mon, 06 Feb 2012 01:51:35 PST

Presently, DC motors are the actuator of choice within intelligent upper limb prostheses. However, the weight and dimensions associated with suitable DC motors are not always compatible with the geometric restrictions of a prosthetic hand; reducing available degrees of freedom and ultimately rendering the prosthesis uncomfortable for the end-user. As a result, the search is on-going to find a more appropriate actuation solution that is lightweight, noiseless, strong and cheap. Shape memory alloy (SMA) actuators offer the potential to meet these requirements. To date, no viable upper limb prosthesis using SMA actuators has been developed. The primary reasons lie in low force generation as a result of unsuitable actuator designs, and significant difficulties in control owing to the highly nonlinear response of SMAs when subjected to joule heating. This work presents a novel and comprehensive methodology to facilitate evaluation of SMA bundle actuators for prosthetic finger design. SMA bundle actuators feature multiple SMA wires in parallel. This allows for increased force generation without compromising on dynamic performance. The SMA bundle actuator is tasked with reproducing the typical forces and contractions associated with the human finger in a prosthetic finger design, whilst maintaining a high degree of energy efficiency. A novel approach to SMA control is employed, whereby an adaptive controller is developed and tuned using the underlying thermo-mechanical principles of operation of SMA wires. A mathematical simulation of the kinematics and dynamics of motion provides a platform for designing, optimizing and evaluating suitable SMA bundle actuators offline. This significantly reduces the time and cost involved in implementing an appropriate actuation solution. Experimental results show iii that the performance of SMA bundle actuators is favourable for prosthesis applications. Phalangeal tip forces are shown to improve significantly through bundling of SMA wire actuators, while dynamic performance is maintained owing to the design and implementation of the selected control strategy. The work is intended to serve as a roadmap for fellow researchers seeking to design, implement and control SMA bundle actuators in a prosthesis design. Furthermore, the methodology can also be adopted to serve as a guide in the evaluation of other non-conventional actuation technologies in alternative applications.

Numerical Prediction of the Haemodynamic Impact of Coronary Stent Implantation

Jonathan Murphy (Thesis) — Thu, 24 Nov 2011 06:58:32 PST

Arterial restenosis limits the effectiveness of coronary stenting. Restenosis is caused by excessive tissue growth which is stimulated by arterial injury and alterations to the arterial WSS. The altered WSS results from stent-induced disturbances to the natural haelnodynamics of the artery. Recent numerical studies have predcted only minor digerences in altered WSS between different stent designs using a commonly employed threshold assessment technique. While it is possible that there are only minor differences, it is more likely that the assessment technique is incapable of fully elucidating the altered WSS created by stent implantation. This thesis proposes a methodology that involves a more complete level of investigation into the stentinduced alterations to the WSS by incorporating the full suite of WSS-based variables: WSS, WSS gradient (WSSG), WSS angle gradient (WSSAG) and oscillatory shear index (OSI). Each of these variables highlights a different type of alteration to the arterial WSS that could lead to excessive tissue growth. The four variables are analysed quantitatively and qualitatively using statistical methods to assess the effect of the stent implantation. The methodology is applied to three stents with contrasting designs: the Palinaz-Schatz (PS), the Gianturco-Roubin II (GR-11) and the Bx-Velocity (Bx) stents. From the results, the sients are ranked (best to worst) for WSS: GR-11, PS, Bx (Cohen's d: -0.01, -0.6131, for WSSG: PS, Bx, GR-I1 (d: 0.159,0.764), for WSSAG: PS GR-I1 Bx (d: 0.213, 0.082), and for OSI: PS, GR- 11, Bx (d: 0.3 15, 0.380). The proposed method of analysis is shown to elucidate the alterations to the WSS created by the stents to a far greater level than with the previously used threshold technique. This method of stent assessment could be utilised to minimise WSS alterations at the design stage of future bare metal, as well as permanent and bioabsorbable drug-eluting coronary stents.

Liquid Crystal Devices for Optical Communications and Sensing Applications

Sunish Mathews (Thesis) — Tue, 22 Nov 2011 06:44:45 PST

This thesis is focussed on the design and development of liquid crystal based tunable photonic devices for applications in optical communications and optical sensing, with an emphasis on all-fiber device configuration. The infiltration of liquid crystals into photonic crystal fiber provides a suitable common platform to design and fabricate simple and compact all-fiber tunable photonic devices which can be easily integrated with optical fiber networks and sensing systems. Based on the infiltration of liquid crystals – materials with high dielectric anisotropy, into photonic crystal fibers a common platform is developed to address the need for electronically tunable photonic devices with a compact all-fiber device configuration. A ferroelectric liquid crystal based tunable filter is theoretically studied and experimentally demonstrated for applications in the demodulation of multiple Fiber Bragg Grating sensors. The electrical tunability of liquid crystal infiltrated photonic crystal fiber is employed for the development of all-fiber tunable photonic devices for a variety of applications in optical communication systems. A nematic liquid crystal infiltrated photonic crystal fiber based all-fiber broadband electronically controlled variable optical attenuator is demonstrated in the wavelength range from 1500 nm – 1600 nm. With smectic liquid crystal infiltration the electrical tuning of photonic bandgap is achieved and an all-fiber tunable notch filter for applications in optical communication is demonstrated. A novel technology for all-fiber based electric field sensing is developed with the use of nematic liquid crystal infiltrated photonic crystal fibers. A simple and compact all-fiber sensor head is demonstrated, which allows for the accurate measurement of electric field intensity, along with detection and measurement of electric field signal parameters such as frequency, amplitude and also the direction of the electric field. Studies performed on the transmission and reflection responses of the sensor, demonstrate the capability of the simple and compact all-fiber electric field sensor to operate in both in-line and end-point type configurations. The effect of the applied electric field frequency on the propagation properties of liquid crystal infiltrated photonic crystal fiber is studied in the range from 50 Hz to 1 kHz. With the use of a suitable fitting function on the time varying transmission response of the fiber, it is demonstrated that the parameters of the applied electric field such as frequency and amplitude can be measured. Selectively infiltrated photonic crystal fibers are studied in a polarimetric electric field sensing scheme and it is demonstrated that the optimization of the length of the infiltrated section of the photonic crystal fiber subjected to an electric field allows to obtain a linear transmission response for the sensor in a given electric field range. The directional electric field sensitivity of a liquid crystal infiltrated elliptical core photonic crystal fiber is studied and a true all-fiber directional electric field sensor is demonstrated which is capable of simultaneous detection and measurement of the amplitude and direction of an applied electric field.

Antenna Development for Radio Frequency Hyperthermia Applications

Sergio Curto (Thesis) — Wed, 02 Nov 2011 08:58:16 PDT

This thesis deals with the design steps, development and validation of an applicator for radio frequency hyperthermia cancer therapy. An applicator design to enhance targeted energy coupling is a key enabler for preferential temperature increments in tumour regions. A single-element, near-field approach requires a miniaturised solution, that addresses ergonomic needs and is tolerant to patient anatomy. The antenna war-field rriodality and the high-dielectric patient loading introduce significant analytical and computational resource challenges. The antenna input impedance has to be sufficiently insensitive to in-band resonant cletuning and the fields in the tissue can he targeted to selected areas in the patient. An introduction to the medical and biological background of hyperthermia is presented. The design requirements of antennas for medical and in particular for hyperthermia applications are highlighted. Starting from a conventional circular patch, the antenna evolved into a compact circular patch with a concentric annular ring and slotted groundplane, operating at the 434 MHz Industrial Scientific and Medical frequency band. Feed point location is optimized for an energy deposition pattern aligned with the antenna centre. The applicator is assessed with other published approaches and clinically used loop, dipole and square patch antennas. The antennas are evaluated for the unloaded condition and when loaded with a tri-layer body tissue numerical model. This model comprises skin, fat and transverse fiber of muscle of variable thicknesses to account for different body locations and patient. anatomy. A waterbolus containing de-ionized water is added at the skin interface for superficial tissue cooling aud antelina matching. The proposed applicator achieves a penetration depth that supersedes other approaches while remaining compact and an ergonomic fit to tumour areas on the body. To consider the inner and peripheral complex shapes of human bodies, the full human body numerical model developed by Remcom is used. This model was segmented from 1 mm step computed tomography (CT) and magnetic resonance imaging (MRI) cross-sections through and adult male and it comprises twenty-three tissue types with thermal and frequency-dependent dielectric properties. The applicator performance is evaluated at three anatomical body areas of the model to assess its suitability for treatment of tumours at different locations. These three anatomical regions present different aperture coupling and tissue composition. 'Different conformal waterbolus and air gap thickness values are evaluated. The models used in this work are validated with measurements performed in a phantom containing a lossy liquid with dielectric properties representative of homogeneous human body tissue. The dosimetric assessment system (DASY) is used to evaluaxe the specific absorption rate (SAR) generated for the antenna into the liquid. The measurement setup with the antenna, phantom and liquid are simulated. Simulated and measured results in terrms of specific absorption rate and return loss are evaluated.

Performance and Policy Evaluation of Solar Energy Technologies for Domestic Application in Ireland

Lacour Ayompe (Thesis) — Tue, 11 Oct 2011 06:59:18 PDT

The aim of this research is to investigate the techno-economic and environmental performance of domestic scale grid-connected photovoltaic (PV) and forced circulation solar water heating (SWH) systems in Ireland; and propose a new feed-in tariff designed using a large sample of high resolution electricity demand data in order to provide credible information for informed policy formulation. Detailed field trials of experimental installations of a 1.72 kWp grid-connected PV and two SWH systems (with 4 m2 flat plate and 3 m2 heat pipe evacuated tube collectors) were undertaken to collect data. The energy, economic and environmental performances of the systems was evaluated. Energy balance models for the systems were developed and validated using performance data. Drawing upon system performance data, the implications for policy formulation in Ireland were discussed. Results from the economic analysis on six commercially available sizes of gridconnected PV systems and the two SWH systems equipped with different types of auxiliary heating systems revealed that they are not yet economically viable in Ireland under the existing support policies and assumptions considered. However, projecting current system costs into the future using technology learning rates and market data revealed that some of the systems become economically viable at a later stage under different scenarios. Alternative policies were explored and a new feed-in tariff was designed that guarantees 50% market penetration for domestic scale PV system sizes. Grid parity between retail and wholesale electricity prices was projected to occur in 2023 and 2025 respectively under the best scenarios. A look at the marginal abatement costs for the PV and SWH systems show that on a purely economic basis, it does not make sense to promote investment in domestic-scale PV systems in Ireland now, since Ireland would have very little impact on the technology learning curves and thus system costs being a small market. However, existing policy support for solar thermal systems should be sustained since it improves the economic viability of SWH systems.

Investigation to Improve the Control and Operation of a Three-phase Photovoltaic Grid-tie Inverter

Moin Hanif (Thesis) — Fri, 07 Oct 2011 02:56:22 PDT

Solar Energy or more precisely photovoltaic energy is one of the most promising sources of electricity for the future and it can be used as a distributed generator (DG) to play its role in ‘smart grids of the future’. Distributed PV (photovoltaic) generators can provide numerous potential benefits such as augmenting the capacity of distribution systems, deferring capital investments on distribution and transmission (T&D) systems and improving power quality and system reliability. The PV energy which possesses very special I-V and P-V characteristics has to be conditioned by a PV inverter before it can be consumed by an ac load and/or the grid. Technical improvements in maximum power point tracking (MPPT) and islanding detection are proposed for a three-phase photovoltaic grid tied inverter (GTI) keeping in mind the requirements of the international standards for connecting a DG to the utility grid. This PhD thesis will contain four major sections which are briefed below. A three phase GTI has been simulated using Matlab/Simulink to test the various control blocks and algorithms involved in the building of the power conditioning unit. A DS1104 dSpace DSP controlled, 5.625 kW three-phase GTI laboratory prototype has then been built. Various hardware components, including inverter switches, gate drivers, LCL filter, rectified dc source, boost circuit, transformer, 16A current protection circuit, additional sensing interface circuits and PWM level shifter have been designed and built within the laboratory. The software algorithm created in Simulink communicates directly with the built hardware via the graphical user interface that has been designed with dSPace Control Desk. Algorithms have been developed for the inverter in order to protect it from operating out of nominal frequency and voltage ranges. An algorithm has been developed iii to ensure the boost dc link voltage is controlled to 300V when dc voltage source varies between 150V and 265V. The Z-Source inverter (ZSI), with nine operating states that employs an extra shoot through (ST) state compared to the eight states (6 active and 2 zero states) in traditional VSI is one of the most recent boost topologies that has been proposed in the literature. A step by step design procedure of a ZSI has been developed. A topology comparison between Z-Source inverter and dc-dc boost with VSI is done using literature and simulations. Merits and demerits of the two topologies are summarised and the choice of the topology is justified. MPPT is a process by which maximum power from a PV panel or array is tracked and absorbed during a particular weather condition (insolation level and temperature). There are various MPPT techniques in the literature which are reviewed and a new MPPT approach based on the P&O (Perturb and Observe) method is proposed. The proposed technique is tested on the three phase GTI simulation, it is analysed and compared to the conventionally reviewed P&O MPPT approach. The issue of islanding of GTI’s has raised concerns of equipment and personal safety, for which reason the inverter has to detect and stop the inverter during loss of grid. Passive techniques can detect the grid failure quite well when there is a large power mismatch between the DG and the load but not when the mismatch is small. Active techniques can work well with lower levels of power mismatch but they degrade power quality by introducing disturbances into the power system. A novel wavelet based antiislanding technique is proposed and incorporated into the running hardware protection. This uses physical measurements to reduce the non-detection zone close to zero and keep the power quality of the inverter output unchanged. The developed algorithms have been validated in the laboratory prototype and yield very satisfactory performance.

Thermal Robotic Arm Controlled Spraying via Robotic Arm and Vision System

Dermot Breen (Thesis) — Wed, 05 Oct 2011 07:17:43 PDT

The Tribology Surface Engineering industry is a worldwide multi billion euro industry with significant health and safety risks. The thermal spraying sector of this industry employs the technique of applying molten surface coating material to a substrate via a thermal spray process which is implemented either by manual spraying or pre-programmed robotic systems. The development of autonomous robotic systems for thermal spraying surface coating would significantly improve production and profitability over pre-programmed systems and improve health and safety over manual spraying. The aim of this research was to investigate and develop through software simulation, physical modelling and testing the development of robotic subsystems that are required to provide autonomous robotic control for the thermal spraying process. Computer based modelling programs were developed to investigate the control strategy identified for the thermal spaying process. The algorithms included fifth order polynomial trajectories and the complete dynamic model where gravitational, inertia, centrifugal and coriolis torques are considered. Tests provide detail of the load torques that must be driven by the robot electric actuator for various structural changes to the thermal spraying robot and for variations in trajectory boundary conditions during thermal spraying. The non-linear and coupled forward and inverse kinematic equations of a five axis articulated robot with continuous rotation joints were developed and tested via computer based modelling and miniature physical robot modelling. Both the computer based modelling and physical model confirmed the closed form kinematic solutions. A solution to running cables through the continuous rotation joints for power and data is present which uses polytetrafloraethylene (PTFE) electroless nickel. This material was identified during the literature review of surface coating materials. It has excellent wear, friction and conductivity properties. Physical tests on a slip ring and brushes test rig using electroless nickel are presented which confirm the viability of using PTFE electroless nickel as a slip ring. Measurement of the substrate during thermal spraying so as to autonomously control the thermal spaying robot is a significant challenge. This research presents solutions for the measurement of the substrate using a low cost camera system and lasers in a single wavelength environment. Tests were carried out which resulted in the removal of a butane flame obscuring a test piece requiring measurement from the camera image so that substrate measurements can be made using image processing and analysis techniques such as canny edge detection and centroid measurements. Test results for the low cost vision system provide depth measure errors of ±0.6 % and structural measurements such as area and perimeter in the range -5% to -7.5%. These results confirm the efficacy of this novel flame removal technique.

Local Urban Interventions and their Role in Economic Development. an Evaluation of Key Policy Inputs based upon Irish and Polish Approaches Supported by European Union Initiatives 1992-2002

Izabela Litewska (Thesis) — Mon, 03 Oct 2011 08:17:26 PDT

The importance of local economies, based on a bottom-up approach, has been increasingly prioritised by urban policy makers as the vital factor that conditions economic development. Modern policy approaches, which are explored in this research, regard local economic development as a process deriving from both, market processes impacting upon local structures, functions and spatial planning, and non-market dimensions based on environmental and social measures. Since the 1990s, both Dublin in Ireland and Upper Silesia in Poland have represented urban regions where economic and social deprivation is being addressed by a range of area-based initiatives but from different perspectives. The research examines in detail the administrative processes involved in treating related developmental problems in similar but contrasting European urban contexts during the period of 1992-2002, a time of intense transition in both the Irish and Polish economy. It explores in practice the difficulties in achieving an integrated approach and how policy makers and service providers adapt to such goals. This could contribute to a wider debate by providing an assessment of the formulation, implementation and likely future impacts of innovative policies in enhancing local economic development during current economic restructuring.

A Cross-Layer Modification to the DSR Routing Protocol in Wireless Mesh Networks

Mustafa Ramadhan (Thesis) — Tue, 06 Sep 2011 04:46:00 PDT

A cross-layer modification to the DSR routing protocol that finds high throughput paths in WMNs has been introduced in this work. The Access Efficiency Factor (AEF) has been introduced in this modification as a local congestion avoidance metric for the DSR routing mechanism as an alternative to the hop count (Hc) metric. In this modification, the selected path is identified by finding a path with the highest minimum AEF (max_min_AEF) value. The basis of this study is to compare the performance of the Hc and max_min_AEF as routing metrics for the DSR protocol in WMNs using the OPNET modeler. Performance comparisons between max_min_AEF, Metric Path (MP), and the well known ETT metrics are also carried out in this work. The results of this modification suggest that employing the max_min_AEF as a routing metric outperforms the Hc, ETT, and MP within the DSR protocol in WMNs in terms of throughput. This is because the max_min_AEF is based upon avoiding directing traffic through congested nodes where significant packet loss is likely to occur. This throughput improvement is associated with an increment in the delay time due to the long paths taken to avoid congested regions. To overcome this drawback, a further modification to the routing discovery mechanism has been made by imposing a hop count limit (HCL) on the discovered paths. Tuning the HCL allows the network manager to tradeoff throughput against delay. The choice of congestion avoidance metric exhibits another shortcoming owing to its dependency on the packet size. It penalises the smaller packets over large ones in terms of path lengths. This has been corrected for by introducing a ModAEF metric that explicitly considers the size of the packet. The ModAEF metric includes a tuning factor that allows the operator determine the level of the weighting that should be applied to the packet size to correct for this dependence.