Publication Search Results

Now showing 1 - 10 of 150

  • (2010) Timms, W. A.; Badenhop, A. M.; Rayner, D. S.; Mehrabi, S. M.

  • (2010) Forbes, Gareth Llewellyn; Randall, Robert Bond
    Conference Paper
    This paper presents a summary of a recent research program, focusing on a new method of non contact gas turbine blade vibration measurement using casing pressure and vibration signals. Currently the dominant method of non contact measurement of turbine blade vibrations employs the use of a number of proximity probes located around the engine periphery measuring the blade tip (arrival) time (BTT). Despite the increasing ability of this method there still exist some limitations, viz: the requirement of a large number of sensors for each engine stage, difficulties in dealing with multiple excitation frequencies, sensors being located in the gas path, and the inability to directly measure the natural frequency of a given blade. Simulations established with a physics based model along with experimental measurements are presented in this paper, using internal pressure and casing vibration measurements, which have the potential to rectify some of these problems.

  • (2010) Djukic, Luke Philip
    Thermoset Composite Welding (TCW) is a process designed specifically for joining composite materials, developed by the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS). The TCW manufacture process is carried out at higher temperatures than those used in service, causing thermal residual (TR) stresses to develop in the joints. An investigation of the strength of single-lap shear joints (SLJs), and the development of laminate free edge microcracks (LFEMs) is presented in this thesis. The reported investigations are primarily experimental. Finite element analysis has been used to understand observations where appropriate. The effect of TR stresses on static failure of TCW SLJs and Cytec FM1515 thin film epoxy adhesive SLJs over the temperature range of -55°C to 71°C is investigated. At temperatures where the joining material is ductile, plastic flow results in the redistribution of TR stresses within the joints, reducing their effect on the failure strength. No such stress redistributions occur at lower temperatures when the joining material is brittle; hence, the TR stresses cause strength reductions. These results were used to propose a method of shear strength improvement by initiating plastic flow in the joint at the time of manufacture. Microcracks are common at the free edges of thermoset composites. These develop preferentially near the weld material interface in TCW laminates, and are termed laminate free edge microcracks (LFEMs) in this study. MicroCT scanning was used to find and characterise LFEMs in TCW joints. The results indicated that TR stresses combined with the free edge sectioning process cause their development outside the joint overlap regions. Microcracks developed within the joint overlaps during mechanical fatigue cycling. LFEMs were also found in FM1515 joints. A fatigue life study is presented for TCW and FM1515 SLJs at -55°C, in which the effect of LFEMs is considered. TCW is a new process. This investigation is the first dealing with the effect of thermal residual stresses on the strength of TCW joints, and the development and effect of LFEMs. The shear strength improvement method is also a novel concept for joints.

  • (2010) Botros, Andrew
    Effective cochlear implant fitting (or programming) is essential for providing good hearing outcomes, yet it is a subjective and error-prone task. The initial objective of this research was to automate the procedure using the auditory nerve electrically evoked compound action potential (the ECAP) and machine intelligence. The Nucleus® cochlear implant measures the ECAP via its Neural Response Telemetry (NRT™) system. AutoNRT™, a commercial intelligent system that measures ECAP thresholds with the Nucleus Freedom™ implant, was firstly developed in this research. AutoNRT uses decision tree expert systems that automatically recognise ECAPs. The algorithm approaches threshold from lower stimulus levels, ensuring recipient safety during postoperative measurements. Clinical studies have demonstrated success on approximately 95% of electrodes, measured with the same efficacy as a human expert. NRT features other than ECAP threshold, such as the ECAP recovery function, could not be measured with similar success rates, precluding further automation and loudness prediction from data mining results. Despite this outcome, a better application of the ECAP threshold profile towards fitting was established. Since C-level profiles (the contour of maximum acceptable stimulus levels across the implant array) were observed to be flatter than T-level profiles (the contour of minimum audibility), a flattening of the ECAP threshold profile was adopted when applied as a fitting profile at higher stimulus levels. Clinical benefits of this profile scaling technique were demonstrated in a 42 subject study. Data mining results also provided an insight into the ECAP recovery function and refractoriness. It is argued that the ECAP recovery function is heavily influenced by the size of the recruited neural population, with evidence gathered from a computational model of the cat auditory nerve and NRT measurements with 21 human subjects. Slower ECAP recovery, at equal loudness, is a consequence of greater neural recruitment leading to lower mean spike probabilities. This view can explain the counterintuitive association between slower ECAP recovery and greater temporal responsiveness to increasing stimulation rate. This thesis presents the first attempt at achieving completely automated cochlear implant fitting via machine intelligence; a future generation implant, capable of high fidelity auditory system measurements, may realise the ultimate objective.

  • (2010) Anprasertporn, Amornrat
    This thesis evaluates the MicroFoss system, also known as the BioSys or the SolerisÒ system, as a rapid method for microbiological analyses of eggs and egg products. Commercially assays for assessment of microbiological quality and sanitation conditions during processing, which are total viable counts (TVC), coliforms and Escherichia coli, are evaluated in comparison to the cultural methods. Concurrently, this thesis reports development of a new medium for the MicroFoss Salmonella detection, since this test is not available. Good correlations between the cultural TVCs and the MicroFoss detection times (DTs) were obtained (r ³-0.84) in all egg products. Preliminary results of a correlation between the cultural TVCs dominated by Pseudomonas fluorescens and the MicroFoss DTs suggested that the MicroFoss could be used for investigation of spoilage and shelf life prediction of eggs. High agreements (r ³-0.93) between the MicroFoss and cultural methods for coliforms and E. coli in eggs and egg products was achieved as well as the accuracy, sensitivity and specificity. The MicroFoss for estimations of TVC, coliforms and E. coli could be completed in less than 24h, compared to 48-72h required for the cultural methods. Hence, the MicroFoss could be used as a rapid screening for quality control of eggs and egg products. While a new propylene glycol-based selective medium developed was effective for detection of Salmonella, possible false positive results caused by certain bacteria, such as Enterobacter cloacae, E. coli, Klebsiella pneumoniae and Proteus mirabilis, were encountered. When this selective medium was supplemented with 40 mg/L of novobiocin, or 1 or 2 mL/L of Niaproof 4, these non-salmonellae were greatly suppressed or eliminated, particularly Pr. mirabilis, whilst this did not affect growth of Salmonella. Various serotypes of Salmonella including strains of atypical biotype were able to acidify propylene glycol in these media. Detection of Salmonella in naturally contaminated eggs by the MicroFoss using propylene glycol-based selective media showed equivalent sensitivity and specificity to the Australian Standard 5013.10-2004, according to numbers of egg samples tested in this study. Detection of low level of Salmonella (1-10 CFU/25g of eggs pre-enriched in buffered peptone water) was achieved in less than 24h.

  • (2010) Alshroof, Osama Nayef Abdallah
    The significant increase in heat fluxes rejected from electronic equipment and other small devices has continued with the unrelenting demand for technological improvement. There is therefore a need to increase the performance of the heat exchangers operating at these small scales. Consequently, the flow in these heat exchangers is likely to be laminar, resulting in poor thermal performance. Hence, some means of heat transfer enhancement is needed. It appears that protrusion and dimples may sufficiently increase heat transfer rates without a large pressure drop penalty. A comprehensive numerical study was undertaken of the flow and thermal fields along with the heat transfer distribution in the vicinity of isolated, height to print diameter ratio (h/D=0.22 and 0.5) spherical dimples and protrusions in shallow rectangular channels. The purpose of the study was to develop an understanding of flow structures, the resultant thermal fields and heat transfer in the vicinity of a single obstacle. In addition, different combinations of small and large dimples and protrusions have been investigated in order to obtain a comprehension of effect of the interaction between the flow fields of these heat transfer enhancement devices when placed in an array. The numerical approach used in this research was validated by the excellent agreement between the velocity and thermal fields generated by the computer code when modelling the flow and heat transfer in a shallow rectangular channel containing a large protrusion and the experimental data obtained by particle image velocimetry and thermochromic liquid crystal sheets. For the range of Reynolds numbers and channel aspect ratios studied the flow around the small protrusion and dimple is steady. However, these small obstacles generated surprisingly complex flow structures and concomitant thermal fields. When the large protrusion is used the flow becomes unsteady at a critical Reynolds number. A thorough study of the unsteady and time-averaged flow and temperature fields are presented as well as the resultant heat transfer distributions on the channel surfaces at a Reynolds number of 1600. Similar studies were performed for the steady flow in the vicinity of isolated large dimple. The introduction of a single small protrusion in a shallow rectangular channel leads to a larger enhancement in heat transfer than a single small dimple. This enhancement is dependent on Prandtl and Reynolds numbers. Whilst a similar result is found when isolated large protrusions and dimples are employed, the average augmentation achieved when the large protrusion is used is four times that obtained when a small protrusion is employed at the same Reynolds number. This massive heat transfer enhancement wit ha large protrusion is associated with an effectiveness factor of 1.7 in contrast with 1.15 for the small protrusion; making the large protrusion a cost effective method of heat transfer enhancement. As a result, a number of large protrusion/dimple combinations were studied in order to develop an understanding of the interactions between the flow fields developed by individual obstacles so as to be able to design arrays which would maximise the heat transfer without producing undesirably high pressure penalties.

  • (2010) Tjahjono, Budi Santoso
    To reach the goal of grid parity, the cost of crystalline solar cells need to be reduced considerably. This can be done by using cheaper materials, such as thinner or lower quality wafers, or by reducing manufacturing costs, both process and material costs. Increasing the efficiencies of the devices while maintaining low costs via simple fabrication schemes is an ideal combination. The benefits of selective emitter have been known and quantified for many years. However, the adaptation of selective emitter solar cell designs into mass-production has been quite slow due to the relatively complex processing steps involved in applying such a design. This thesis begins with a review of various existing selective emitter solar cell technologies. A method of creating a selective emitter is then selected to be the main focus of the thesis due to its simple yet powerful features. This method is laser-doping through a dielectric layer. A new solar cell structure that employs the laser-doping process combined with a self-aligned metallisation method is then introduced, termed Laser-Doped Selective Emitter (LDSE) solar cell. A study is then presented to help further understanding of the laser-doping through dielectric process. Investigative work combines the use of defect Yang etch, SEM and EBIC analysis, light JV curve measurements and local ideality factor derived from dark JV curve measurements. These investigations help to identify several challenges associated with the laser-doping process. Theories on the causes of these challenges are then presented along with possible solutions. One of the most critical findings is the use of a stacked layer consisting of a thin layer of thermally grown SiO2 and PECVD SiNx to prevent laser-induced defects. Next, several characterisation methods that include four point-probes, Secondary Ion Mass Spectrometry (SIMS), spreading sheet resistance, Electron Beam Induced Current (EBIC) analysis and photoluminescence imaging are utilised to measure the sheet resistances, doping profiles and lifetime of the laser-doped region. These measurement techniques are used to optimise the laser parameters and other processing parameters involved in the fabrication of LDSE solar cells. In the final chapter, a novel self-aligned metallisation method that utilises the solar cell’s ability to produce voltage and current is investigated. It is found that this photoplating method is well-suited for fabrication of LDSE cells and potentially suitable in mass-production. Finally, the integration of the optimised process flow and parameters combined with the photoplating method is demonstrated through the fabrication and characterisation of a batch of LDSE solar cells made of commercial 125mm 1 Ω.cm p-type wafers. Efficiencies of up to 19% with VOC in excess of 635 mV and JSC close to 38 mA/cm2 are reported on 125 mm commercial grade CZ p-type wafers. The use of typical production line equipments for most of the fabrication steps is also demonstrated.

  • (2010) Hameiri, Ziv
    This thesis examines two different ways to improve the performance of single sided laser-doped solar cells. The first is replacing the aluminum rear contact with localised contacts and a high-quality passivation layer. The second is optimising the laser processing to minimise any detrimental effects. It is demonstrated that annealing in the 600-820°C range significantly improves the passivation of different SiNx films on different silicon surfaces. Significant bulk lifetime enhancement is seen when SiNx-passivated CZ wafers are annealed. Using an optimal annealing condition, the implied Voc of CZ silicon substrates increased to a value comparable to that of FZ wafers - almost 720 mV. Laser-induced defects are investigated using a wide range of characterisation techniques. It is found that laser doping degrades the electrical performance of the device. This degradation is more pronounced when a dielectric layer is present during the laser process, possibly due to the thermal expansion mismatch between the silicon and the overlying dielectric layer. Methods to reduce defect density are discussed. The influence of laser parameters on the electrical performance of laser-doped solar cells is studied. It is demonstrated that a wide range of laser diode currents can be used to create a p-n junction by laser doping. Grooves formed through intermediate levels of ablation can be used to improve the adhesion between the silicon and metal without significantly degrading the cell performance. Electroless and photo-plating are compared; higher pseudo-FFs are achieved for photoplated laser-doped solar cells. If the photoplating technique is combined with well-optimised Ni sintering, the pseudo-FF is almost independent of the laser diode current. A new double sided laser-doped structure is developed. This structure is based on silicon nitride passivation of the rear surface and the formation of a selective emitter and local back-surface field by laser doping. One-sun implied Voc above 680 mV is achieved on commercial grade CZ p-type wafers when measured after laser doping and prior to metallisation. This is ~50 mV higher than the Voc obtained for the single-sided laser-doped cell at the same stage. This high Voc demonstrates the potential of this structure to achieve efficiencies exceeding 20%.

  • (2010) Ji, Philip Nan
    As the backbone for the global communication network, optical dense wavelength division multiplexed (DWDM) systems are facing challenges in capacity, flexibility, reliability and cost effectiveness. In my thesis research I developed five novel optical devices or subsystems to combat these technical challenges. Each of these devices/subsystems is described in an individual chapter including background survey, proposal of new features, theoretical analysis, hardware design, prototype fabrication and characterization, and experimental verification in DWDM systems. The first is a novel tunable asymmetric interleaver that allows the interleaving ratio to be adjusted dynamically. Two design methods were proposed and implemented. Spectral usage optimisation and overall system performance improvement in 10G/40G and 40G/100G systems were successfully demonstrated through simulations and experiments. The second is a colourless intra-channel optical equalizer. It is a passive periodic filter that restores the overall filter passband to a raised cosine profile to suppress the filter narrowing effect and mitigate the inter-symbol interference. 20% passband widening and 40% eye opening were experimentally achieved. The third is a flexible band tunable filter that allows simultaneous tuning of centre frequency and passband width. Based mainly on this filter, a low cost expendable reconfigurable optical add/drop multiplexer (ROADM) node was developed. Its flexible switching features were experimentally demonstrated in a two-ring four-node network testbed. The fourth is a transponder aggregator subsystem for colourless and directionless multi-degree ROADM node. Using the unique characteristics of the coherent receiver, this technology eliminates the requirement of wavelength selector, thus reduces power consumption, size and cost. I experimentally demonstrated that it can achieve < 0.5 dB penalty between receiving single channel and 96 channels. The last is a real-time feedforward all-order polarization mode dispersion (PMD) compensator. It first analyses spectral interference pattern to retrieve phase information and calculate PMD, then it uses a pulse shaper to restore the pulse shape and thus compensates the PMD. These functions were demonstrated through experiments and simulations. All of these novel devices and subsystems deliver new functional features and are suitable to be applied in the next generation DWDM systems to improve capacity, flexibility, and reliability and to reduce cost.