Optical In-Process Measurement Systems

Information is key, which means that measurements are key. For this reason, this book provides unique insight into state-of-the-art research works regarding optical measurement systems. Optical systems are fast and precise, and the ongoing challenge is to enable optical principles for in-process measurements. Presented within this book is a selection of promising optical measurement approaches for real-world applications

Low-Cost, Water Pressure Sensing and Leakage Detection Using Micromachined Membranes

This work presents the only known SOI membrane approach, using Microelectromechanical systems (MEMS) fabrication techniques, to address viable water leakage sensing requirements at low cost. In this research, membrane thickness and diameter are used in concert to target specific stiffness values that will result in targeted operational pressure ranges of approximately 0-120 psi. A MEMS membrane device constructed using silicon-on-insulator (SOI) wafers, has been tested and packaged for the water environment. MEMS membrane arrays will be used to determine operational pressure range by bursting.Two applications of these SOI membranes in aqueous environment are investigated in this research. The first one is water pressure sensing. We demonstrate that robustness of these membranes depends on their thickness and surface area. Their mechanical strength and robustness against applied pressure are determined using Finite Element Analysis (FEA). The mechanical response of a membrane pressure sensor is determined by physical factors such as surface area, thickness and material properties. The second application of this device is water leak detection. In devices such as pressure sensors, microvalves and micropumps, membranes can be subjected to immense pressure that causes them to fail or burst. However, this event can be used to indicate the precise pressure level that malfunction occurred. These membrane arrays can be used to determine pressure values by bursting. We discuss the background information related to the proposed device: MEMS fabrication processes (especially related to proposed device), common MEMS materials, general micromachining process steps, packaging and wire bonding techniques, and common micromachined pressure sensors. Besides, FEA on SOLIDWORKS simulation module is utilized to understand membrane sensitivity and robustness. In addition, we focus on theories supporting the simulated results. We also discuss the device fabrication process, which consists of the tested device’s fabrication process, Deep Reactive Ion Etching (DRIE) for membrane formation, two different realizable fabrication technique (depending on sensing material) of sensing element, metal contact pads, and connectors deposition. In addition, a brief description and operation procedures of the device fabrication tools are provided as well. We also include detailed electrical and mechanical testing procedures and the collected data

Solidification behaviour and mechanical properties of cast Mg-alloys and Al-based particulate metal matrix composites under intensive shearing

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Magnesium alloys, as the lightest of all structural metallic materials, and aluminium-based particulate metal matrix composites (PMMCs), offering unified combination of metallic and ceramic properties, have attracted increased interest from the automotive, aerospace, electronic and recreation industries. Current processing technologies for PMMCs do not achieve a uniform distribution of fine-sized reinforcements and produce agglomerated particles in the ductile matrix, which are detrimental to the ductility. At the same time, molten magnesium alloys contain impurities and oxides and when cast conventionally, the final components usually exhibit a coarse and non-uniform microstructure with various casting defects. The key idea in this thesis has been to adopt a novel intensive melt conditioning process, allowing the application of sufficient shear stress that would disperse solid particles present in the melt and offer unique solidification behaviour, improved fluidity and die-filling during casting. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, where intensive shearing is directly imposed on the alloy melt, which is then cast by the conventional HPDC process, has been used to produce PMMC and magnesium alloy castings. The MC-HPDC process for PMMCs leads to a uniform dispersion of the reinforcement in the matrix, confirmed by quantitative statistical analysis, and increased mechanical performance as indicated by an increase in the hardness and the tensile properties of the composites. We describe a solidification path for aluminium containing magnesium alloys, where intensive shearing prior to casting leads to effective dispersion of solid oxide particles, which then effectively act as nucleation sites for magnesium grains, resulting in significant grain refinement. The MC-HPDC processed magnesium castings have a significantly refined microstructure, with reduced porosity levels and casting defects. Evaluation of the mechanical properties of the castings reveals the beneficial effect of intensive shearing. After careful optimization, the MC-HPDC process shows promising potential for the direct recycling of high purity magnesium die casting scrap, producing casting with mechanical properties comparable to those of primary magnesium alloys

Direct Experimental Observation of 3D Vortex States in Multilayer Fe/Gd using Scanning Electron Microscopy with Polarization Analysis (SEMPA)

The global market for power solely for data center usage is estimated to be $12.4 billion by 2027[1]. In 2021, data center electricity consumption was ∼400 TW h, representing almost 2% of the global energy demand[2]. Ongoing efforts in spintronics, which use spin currents instead of traditional charge currents at a fraction of the power[3], are paving the way for significant savings, both financially and environmentally. There has been considerable research into alternatives for memory[4–6] including a magnetic structure known as a skyrmion, a self-supporting magnetic texture characterized by a non-trivial topology. Recent advances in creating room-temperature stable skyrmions has reignited interest in these objects. Building on previous work in the McMorran group, this research set out to build a more complete understanding of the 3D structure of metastable magnetic skyrmions, specifically in Fe/Gd thin films. This was done using traditional trans- mission electron microscope (TEM) techniques along with a unique scanning elec- tron microscope with polarization analysis at the University, the SEMPA. Data col- lected using a TEM in Lorentz mode, providing information integrated through the bulk of the material, was combined with data from SEMPA, providing surface- sensitive information about the top of the material. Analysis of the data suggests atopologically complex winding nature for the magnetization of skyrmions in this material. Presented herein is a brief introduction of the magnetic structures found in Fe/Gd multilayer thin films; an analysis using new analytical tools built for this purpose of the data collected; and a user’s manual for SEMPA, including mainte- nance and troubleshooting guidance

Virtual metrology for plasma etch processes.

Plasma processes can present dicult control challenges due to time-varying dynamics and a lack of relevant and/or regular measurements. Virtual metrology (VM) is the use of mathematical models with accessible measurements from an operating process to estimate variables of interest. This thesis addresses the challenge of virtual metrology for plasma processes, with a particular focus on semiconductor plasma etch. Introductory material covering the essentials of plasma physics, plasma etching, plasma measurement techniques, and black-box modelling techniques is rst presented for readers not familiar with these subjects. A comprehensive literature review is then completed to detail the state of the art in modelling and VM research for plasma etch processes. To demonstrate the versatility of VM, a temperature monitoring system utilising a state-space model and Luenberger observer is designed for the variable specic impulse magnetoplasma rocket (VASIMR) engine, a plasma-based space propulsion system. The temperature monitoring system uses optical emission spectroscopy (OES) measurements from the VASIMR engine plasma to correct temperature estimates in the presence of modelling error and inaccurate initial conditions. Temperature estimates within 2% of the real values are achieved using this scheme. An extensive examination of the implementation of a wafer-to-wafer VM scheme to estimate plasma etch rate for an industrial plasma etch process is presented. The VM models estimate etch rate using measurements from the processing tool and a plasma impedance monitor (PIM). A selection of modelling techniques are considered for VM modelling, and Gaussian process regression (GPR) is applied for the rst time for VM of plasma etch rate. Models with global and local scope are compared, and modelling schemes that attempt to cater for the etch process dynamics are proposed. GPR-based windowed models produce the most accurate estimates, achieving mean absolute percentage errors (MAPEs) of approximately 1:15%. The consistency of the results presented suggests that this level of accuracy represents the best accuracy achievable for the plasma etch system at the current frequency of metrology. Finally, a real-time VM and model predictive control (MPC) scheme for control of plasma electron density in an industrial etch chamber is designed and tested. The VM scheme uses PIM measurements to estimate electron density in real time. A predictive functional control (PFC) scheme is implemented to cater for a time delay in the VM system. The controller achieves time constants of less than one second, no overshoot, and excellent disturbance rejection properties. The PFC scheme is further expanded by adapting the internal model in the controller in real time in response to changes in the process operating point

Virtual metrology for plasma etch processes.

Plasma processes can present dicult control challenges due to time-varying dynamics and a lack of relevant and/or regular measurements. Virtual metrology (VM) is the use of mathematical models with accessible measurements from an operating process to estimate variables of interest. This thesis addresses the challenge of virtual metrology for plasma processes, with a particular focus on semiconductor plasma etch. Introductory material covering the essentials of plasma physics, plasma etching, plasma measurement techniques, and black-box modelling techniques is rst presented for readers not familiar with these subjects. A comprehensive literature review is then completed to detail the state of the art in modelling and VM research for plasma etch processes. To demonstrate the versatility of VM, a temperature monitoring system utilising a state-space model and Luenberger observer is designed for the variable specic impulse magnetoplasma rocket (VASIMR) engine, a plasma-based space propulsion system. The temperature monitoring system uses optical emission spectroscopy (OES) measurements from the VASIMR engine plasma to correct temperature estimates in the presence of modelling error and inaccurate initial conditions. Temperature estimates within 2% of the real values are achieved using this scheme. An extensive examination of the implementation of a wafer-to-wafer VM scheme to estimate plasma etch rate for an industrial plasma etch process is presented. The VM models estimate etch rate using measurements from the processing tool and a plasma impedance monitor (PIM). A selection of modelling techniques are considered for VM modelling, and Gaussian process regression (GPR) is applied for the rst time for VM of plasma etch rate. Models with global and local scope are compared, and modelling schemes that attempt to cater for the etch process dynamics are proposed. GPR-based windowed models produce the most accurate estimates, achieving mean absolute percentage errors (MAPEs) of approximately 1:15%. The consistency of the results presented suggests that this level of accuracy represents the best accuracy achievable for the plasma etch system at the current frequency of metrology. Finally, a real-time VM and model predictive control (MPC) scheme for control of plasma electron density in an industrial etch chamber is designed and tested. The VM scheme uses PIM measurements to estimate electron density in real time. A predictive functional control (PFC) scheme is implemented to cater for a time delay in the VM system. The controller achieves time constants of less than one second, no overshoot, and excellent disturbance rejection properties. The PFC scheme is further expanded by adapting the internal model in the controller in real time in response to changes in the process operating point

INTEGRATED APPROACH TO THE SUPERPLASTIC FORMING OF MAGNESIUM ALLOYS

The economical and environmental issues associated with fossil fuels have been urging the automotive industry to cut the fuel consumption and exhaust emission levels, mainly by reducing the weight of vehicles. However, customers increasing demands for safer, more powerful and luxurious vehicles have been adding more weight to the various categories of vehicles, even the smallest ones. Leading car manufacturers have shown that significant weight reduction, yet satisfying the growing demands of customers, would not be feasible without the extensive use of lightweight materials. Magnesium is the lightest constructional metal on earth, offering a great potential for weight-savings. However, magnesium and its alloys exhibit inferior ductility at low temperatures, limiting their practical sheet metal applications. Interestingly, some magnesium alloys exhibit superplastic behaviour at elevated temperatures; mirrored by the extraordinarily large ductility, surpassing that of conventional steels and aluminium alloys. Superplastic forming technique is the process used to form materials of such nature, having the ability to deliver highly-profiled, yet very uniform sheet-metal products, in one single stage. Despite the several attractions, the technique is not widely-used because of a number of issues and obstacles. This study aims at advancing the superplastic forming technique, and offering it as an efficient process for broader utilisation of magnesium alloys for sheet metal applications. The focus is primarily directed to the AZ31 magnesium alloy, since it is commercially available in sheet form, possesses good mechanical properties and high strength/weight ratio. A general multi-axial anisotropic microstructure-based constitutive model that describes the deformation behaviour during superplastic forming is first developed. To calibrate the model for the AZ31 magnesium alloy, systematic uniaxial and biaxial stretching tests are carried out over wide-ranging conditions, using 3 specially-designed fixtures. In a collaborative effort thereafter, the calibrated constitutive model is fed into a FE code in conjunction with a stability criterion, in order to accurately simulate, control and ultimately optimise the superplastic forming process. Special pneumatic bulge forming setup is used to validate some proposed optimisation schemes, by forming sheets into dies of various geometries. Finally, the materials post-superplastic-forming properties are investigated systematically, based on geometrical, mechanical and microstructural measures

Solidification behaviour and mechanical properties of cast Mg-alloys and Al-based particulate metal matrix composites under intensive shearing

Magnesium alloys, as the lightest of all structural metallic materials, and aluminium-based particulate metal matrix composites (PMMCs), offering unified combination of metallic and ceramic properties, have attracted increased interest from the automotive, aerospace, electronic and recreation industries. Current processing technologies for PMMCs do not achieve a uniform distribution of fine-sized reinforcements and produce agglomerated particles in the ductile matrix, which are detrimental to the ductility. At the same time, molten magnesium alloys contain impurities and oxides and when cast conventionally, the final components usually exhibit a coarse and non-uniform microstructure with various casting defects. The key idea in this thesis has been to adopt a novel intensive melt conditioning process, allowing the application of sufficient shear stress that would disperse solid particles present in the melt and offer unique solidification behaviour, improved fluidity and die-filling during casting. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, where intensive shearing is directly imposed on the alloy melt, which is then cast by the conventional HPDC process, has been used to produce PMMC and magnesium alloy castings. The MC-HPDC process for PMMCs leads to a uniform dispersion of the reinforcement in the matrix, confirmed by quantitative statistical analysis, and increased mechanical performance as indicated by an increase in the hardness and the tensile properties of the composites. We describe a solidification path for aluminium containing magnesium alloys, where intensive shearing prior to casting leads to effective dispersion of solid oxide particles, which then effectively act as nucleation sites for magnesium grains, resulting in significant grain refinement. The MC-HPDC processed magnesium castings have a significantly refined microstructure, with reduced porosity levels and casting defects. Evaluation of the mechanical properties of the castings reveals the beneficial effect of intensive shearing. After careful optimization, the MC-HPDC process shows promising potential for the direct recycling of high purity magnesium die casting scrap, producing casting with mechanical properties comparable to those of primary magnesium alloys.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Clinical outcomes of ranibizumab treatment in diabetic eye disease

Background: The vascular endothelial growth factor (VEGF) inhibitor ranibizumab is emerging as an efficacious treatment for diabetic macular oedema. Large clinical trials have shown improvements in visual acuity and reduced central retinal thickness. Details of its effect on other retinal functional parameters are lacking. There is a concern that repeated ranibizumab treatment could exacerbate macular ischaemia or lead to global retinal dysfunction by inhibiting physiological isoforms of VEGF. Outcomes of surgery for advanced proliferative retinopathy remain variable and post-operative complications including recurrent haemorrhage can limit visual recovery. VEGF is strongly implicated in the pathogenesis of advanced retinopathy, so VEGF inhibition prior to surgery may improve outcomes. Trials have failed to demonstrate a clear benefit for bevacizumab, so investigation of the licensed intraocular agent ranibizumab represents a logical next step. Aims: To investigate the effects of ranibizumab and laser treatment in diabetic macular oedema on the following parameters: visual acuity, protan and tritan colour contrast sensitivity, 4° and 12° macular sensitivity by microperimetry, electrophysiological indices from pattern and full field electroretinograms. To report structural retinal changes following ranibizumab and laser treatment in terms of qualitative and quantitative optical coherence tomography outcomes, and to quantify macular ischaemia by fluorescein angiography. To investigate the effect on visual acuity at three months post-surgery of ranibizumab pre-treatment in patients undergoing vitrectomy for advanced proliferative diabetic retinopathy. Methods: Randomised clinical trial of intravitreal ranibizumab vs. laser in 36 subjects with centre-involving diabetic macular oedema (The LUCIDATE study). Randomised clinical trial of pre-operative intravitreal ranibizumab vs. subconjunctival saline injection in 30 subjects undergoing vitrectomy-delamination for advanced proliferative diabetic retinopathy (The RaDiVit study). Results: Thirty six subjects with diabetic macular oedema were recruited and 33 completed the trial. Ranibizumab treated subjects gained a mean of 6 letters compared with 0.9 letter loss for laser at 48 weeks. Retinal sensitivity improved in the central macular 4° and 12° in both groups but to a greater extent with ranibizumab. There was no evidence of worsening global retinal dysfunction by electroretinograms in either group. Retinal thickness decreased in both groups: there was a 132 µm reduction in central macular thickness with ranibizumab compared with 103 µm for laser. Fluorescein angiography showed no evidence of significantly increased macular ischaemia in either group. Thirty subjects with advanced proliferative diabetic retinopathy were recruited, underwent surgery, and completed the study. At three months post-surgery, visual acuity in the ranibizumab group was 53 letters compared with 47 letters in the control group. Conclusion: In diabetic macular oedema, there is evidence that ranibizumab leads to greater improvements in visual acuity and retinal sensitivity than laser, with a corresponding greater reduction in retinal thickness. There is no evidence that it worsens macular ischaemia or indices of global retinal electrophysiological function, but larger trials designed to address each of the outcomes investigated here would be required to confirm these findings. In proliferative diabetic retinopathy, there is evidence from this small pilot study that ranibizumab treatment leads to better visual acuity at 3 months post-surgery. An appropriately powered trial would be required to confirm this