Capacitive imaging technique for non-destructive evaluation (NDE)

This thesis describes the development and characterization of a novel NDE methodthe Capacitive Imaging (CI) technique. The CI technique employs a pair of (or multiple) electrodes to form a co-planar capacitor, and uses the fringing quasi-static electric field established across the electrodes to investigate specimens of interest. In general, the CI probe is sensitive to surface and hidden defects in insulating materials, and surface features on conducting materials. The CI technique is advantageous for its non-contact and non-invasive nature, and the capacitive coupling allows the CI technique to work on a wide variety of material properties. The theoretical background to the CI technique has been developed. It is shown that in the frequency range of operation (10 kHz to 1 MHz), the quasi-static approximation is valid and the Maxwell’s Equations describing the general electromagnetic phenomena can be simplified. The practical implementation of the CI system is based on this analysis, and it is shown that the CI technique has features that can complement techniques such as eddy current methods that are already established in NDE. The design principles of the CI probes that are required for an optimum imaging performance have been determined, by considering the key measures of the performance including the depth of penetration, the measurement sensitivity, the imaging resolution and the signal to noise ratio (SNR). It has been shown that the operation frequency is not an influential factor - the performance of the CI probe is determined primarily by the geometry of the probe (e.g. size/shape of the electrodes, separation between electrodes, guard electrodes etc.). Symmetric CI probes with triangular-shaped electrodes were identified as a good general purpose design. Finite Element (FE) models were constructed both in 2D and 3D in COMSOLTM to predict the electric field distributions from CI probes. Effects of thickness of specimen, liftoff distance and relative permittivity value etc were examined using the 2D models. The sensitivity distributions of different CI probes were obtained from the 3D models and were used to characterize the imaging ability of the given CI probes. The fundamental concepts of the CI technique have been experimentally validated in a series of scans where the defects were successfully imaged in insulating (Perspex) and conducting (e.g. Aluminium, Steel and carbon fibre composite) specimens. The detection of corrosion under insulation (CUI) has also been demonstrated. The imaging abilities were assessed by investigating various standard specimens under different situations. The CI technique was then successfully applied to various practical specimens, including glass fibre laminated composites and sandwich structures, laminated carbon fibre composites, corroded steel plate and pipe, and concrete specimens. Further measurements were also conducted using modified CI probes, to demonstrate the wide range of applications of the CI technique

Advanced Energy Harvesting Technologies

Energy harvesting is the conversion of unused or wasted energy in the ambient environment into useful electrical energy. It can be used to power small electronic systems such as wireless sensors and is beginning to enable the widespread and maintenance-free deployment of Internet of Things (IoT) technology. This Special Issue is a collection of the latest developments in both fundamental research and system-level integration. This Special Issue features two review papers, covering two of the hottest research topics in the area of energy harvesting: 3D-printed energy harvesting and triboelectric nanogenerators (TENGs). These papers provide a comprehensive survey of their respective research area, highlight the advantages of the technologies and point out challenges in future development. They are must-read papers for those who are active in these areas. This Special Issue also includes ten research papers covering a wide range of energy-harvesting techniques, including electromagnetic and piezoelectric wideband vibration, wind, current-carrying conductors, thermoelectric and solar energy harvesting, etc. Not only are the foundations of these novel energy-harvesting techniques investigated, but the numerical models, power-conditioning circuitry and real-world applications of these novel energy harvesting techniques are also presented

Capacitive imaging technique for non-destructive evaluation (NDE)

This thesis describes the development and characterization of a novel NDE methodthe Capacitive Imaging (CI) technique. The CI technique employs a pair of (or multiple) electrodes to form a co-planar capacitor, and uses the fringing quasi-static electric field established across the electrodes to investigate specimens of interest. In general, the CI probe is sensitive to surface and hidden defects in insulating materials, and surface features on conducting materials. The CI technique is advantageous for its non-contact and non-invasive nature, and the capacitive coupling allows the CI technique to work on a wide variety of material properties. The theoretical background to the CI technique has been developed. It is shown that in the frequency range of operation (10 kHz to 1 MHz), the quasi-static approximation is valid and the Maxwell’s Equations describing the general electromagnetic phenomena can be simplified. The practical implementation of the CI system is based on this analysis, and it is shown that the CI technique has features that can complement techniques such as eddy current methods that are already established in NDE. The design principles of the CI probes that are required for an optimum imaging performance have been determined, by considering the key measures of the performance including the depth of penetration, the measurement sensitivity, the imaging resolution and the signal to noise ratio (SNR). It has been shown that the operation frequency is not an influential factor - the performance of the CI probe is determined primarily by the geometry of the probe (e.g. size/shape of the electrodes, separation between electrodes, guard electrodes etc.). Symmetric CI probes with triangular-shaped electrodes were identified as a good general purpose design. Finite Element (FE) models were constructed both in 2D and 3D in COMSOLTM to predict the electric field distributions from CI probes. Effects of thickness of specimen, liftoff distance and relative permittivity value etc were examined using the 2D models. The sensitivity distributions of different CI probes were obtained from the 3D models and were used to characterize the imaging ability of the given CI probes. The fundamental concepts of the CI technique have been experimentally validated in a series of scans where the defects were successfully imaged in insulating (Perspex) and conducting (e.g. Aluminium, Steel and carbon fibre composite) specimens. The detection of corrosion under insulation (CUI) has also been demonstrated. The imaging abilities were assessed by investigating various standard specimens under different situations. The CI technique was then successfully applied to various practical specimens, including glass fibre laminated composites and sandwich structures, laminated carbon fibre composites, corroded steel plate and pipe, and concrete specimens. Further measurements were also conducted using modified CI probes, to demonstrate the wide range of applications of the CI technique.EThOS - Electronic Theses Online ServiceUniversity of Warwick. School of EngineeringGBUnited Kingdo

Development of novel high-performance six-axis magnetically levitated instruments for nanoscale applications

This dissertation presents two novel 6-axis magnetic-levitation (maglev) stages that are capable of nanoscale positioning. These stages have very simple and compact structure that is advantageous to meet requirements in the next-generation nanomanufacturing. The 6-axis motion generation is accomplished by the minimum number of actuators and sensors. The first-generation maglev stage is capable of generating translation of 300 ??m in x, y and z, and rotation of 3 mrad about the three orthogonal axes. The stage demonstrates position resolution better than 5 nm rms and position noise less than 2 nm rms. It has a light moving-part mass of 0.2126 kg. The total power consumption by all the actuators is only around a watt. Experimental results show that the stage can carry, orient, and precisely position an additional payload as heavy as 0.3 kg. The second-generation maglev stage is capable of positioning at the resolution of a few nanometers over a planar travel range of several millimeters. A novel actuation scheme was developed for the compact design of this stage that enables 6-axis force generation with just 3permanent-magnet pieces. Electromagnetic forces were calculated and experimentally verified. The complete design and construction of the second-generation maglev stage was performed. All the mechanical part and assembly fixtures were designed and fabricated at the mechanical engineering machine shop. The single moving part is modeled as a pure mass due to the negligible effect of the magnetic spring and damping. Classical as well as advanced controllers were designed and implemented for closed-loop feedback control. A nonlinear model of the force was developed and applied to cancel the nonlinearity of the actuators over the large travel range. Various experiments were conducted to test positioning, loading, and vibration-isolation capabilities. This maglev stage has a moving-part mass of 0.267 kg. Its position resolution is 4 nm over a travel range of 5 ?? 5 mm in the x-y plane. Its actuators are designed to carry and precisely position an additional payload of 2 kg. Its potential applications include semiconductor manufacturing, micro-fabrication and assembly, nanoscale profiling, and nano-indentation

NASA Tech Briefs, September 1997

Topics include: Data Acquisition and Analysis; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Software; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences