Design, Modeling, and Measurement of a Metamaterial Electromagnetic Field Concentrator

This document addresses the need to improve the design process for creating an optimized metamaterial. In particular, two challenges are addressed: creating an electromagnetic concentrator and optimizing the design of metamaterial used to create the electromagnetic concentrator. The first challenge is addressed by developing an electromagnetic field concentrator from a design of concentric geometric shapes. The material forming the concentrator is derived from the application of transformation optics. The resulting anisotropic, spatially variant constitutive parameter tensors are then approximated with metamatieral inclusions using the combination of an AFIT rapid metamaterial design process and a design process created for rapid metamaterial production. The second challenge of optimizing the design of the metamaterial is addressed by considering factors such as circuit board selection, various sets of metamaterial cell geometry combinations, and optimization of the ratio of the widths for the concentric geometric shapes. The resulting optimized design is simulated and shown to compress and concentrate the vertical electric field component of incident plane waves. A physical device is constructed based on the simulations and tested to confirm the entire design process. Experimental data do not definitely show concentration however an optimized design process has been proven

Full-wave modeling of ultrasonic scattering for non-destructive evaluation

The physical modeling and simulation of nondestructive evaluation (NDE) measurements has a major role in the advancement of NDE and structural health monitoring (SHM). In ultrasonic NDE (UNDE) simulations, evaluating the scattering of ultrasound by defects is a computationally-intensive process. Many UNDE system models treat the scattering process using exact analytical methods or high-frequency approximations such as the Kirchhoff approximation (KA) to make the simulation effort tractable. These methods naturally have a limited scope. This thesis aims to supplement the existing scattering models with fast and memory-efficient full-wave models that are based on the boundary element method (BEM). For computational efficiency, such full-wave models should be applied only to those problems wherein the existing approximation methods are not suitable. Therefore, the adequacy of different scattering models for representing various test scenarios has to be studied. Although analyzing scattering models by themselves is helpful, their true adequacy is revealed only when they are combined with models of other elements of the NDE system, and the resulting predictions are evaluated against measurements. Very few comprehensive studies of this nature exist, particularly for full-wave scattering models. To fill this gap, two different scattering models-- the KA and a boundary-element method-- are integrated into a UNDE system model in this work, and their predictions for standard measurement outputs are compared with experimental data for various benchmark problems. This quantitative comparison serves as a guideline for selecting between the KA and full-wave scattering models for performing UNDE simulations. In accordance with theoretical expectations, the KA is shown to be inappropriate for modeling penetrable (inclusion-type) defects and non-specular scattering, such as diffraction from thin cracks above certain angles of incidence. A key challenge to the use of full-wave scattering methods in UNDE system models is the high computational cost incurred during simulations. Whereas the development of fast finite element methods (FEM) has inspired various applications of the FEM for ultrasound modeling in 3D heterogeneous and anisotropic media, very few applications of the BEM exist despite the progress in accelerated BEMs for elastodynamics. The BEM is highly efficient for modeling scattering from arbitrary shaped 3D defects in homogeneous isotropic media due to a reduction in the dimensionality of the scattering problem, and this potential has not been exploited for UNDE. Therefore, building on recent developments, this work proposes a fast and memory-efficient implementation of the BEM for elastic-wave scattering in UNDE applications. This method features three crucial elements that provide robustness and fast convergence. They include the use of (1) high-order discretization methods for fast convergence, (2) the combined-field integral equation (CFIE) formulation for overcoming the fictitious eigenfrequency problem, and (3) the multi-level fast-multipole algorithm (MLFMA) for reducing the computational time and memory resource complexity. Although numerical implementations based on a subset of these three elements are reported in the literature, the implementation presented in this thesis is the first to combine all three. Some numerical examples are presented to demonstrate the importance of these elements in making the BEM viable for practical applications in UNDE. This thesis contains the first implementation of the diagonal-form MLFMA for solving the CFIE formulation for elastic wave scattering without using any global regularization techniques that reduce hypersingular integrals into less singular ones

Ultrasonic nondestructive evaluation of metal additive manufacturing.

Metal Additive Manufacturing (AM) is increasingly being used to make functional components. One of the barriers for AM components to become mainstream is the difficulty to certify them. AM components can have widely different properties based on process parameters. Improving an AM processes requires an understanding of process-structure-property correlations, which can be gathered in-situ and post-process through nondestructive and destructive methods. In this study, two metal AM processes were studied, the first is Ultrasonic Additive Manufacturing (UAM) and the second is Laser Powder Bed Fusion (L-PBF). The typical problems with UAM components are inter-layer and inter-track defects. To improve the UAM process, an in-situ quality evaluation technique was desired. Several NDE techniques were tested in a lab environment before ultrasonic NDE was chosen as a practical, robust, and cost-effective NDE tool. An in-situ monitoring setup was designed and built on an UAM system. NDE results showed interesting features that were simulated through analytic and finite element wave-propagation models. AM layers with defects were characterized as an intact layer and a finite interfacial stiffness spring. The spring stiffness coefficient is a quality parameter that was used to characterize AM layers through a model-based inversion method. In-situ and post-process NDE provided an understanding of defect generation and propagation in UAM. A novel solid-state repair mechanism based on Friction Stir Processing (FSP) was proposed and demonstrated. The quality of L-PBF components depends on several factors including laser power, scan speed, hatch spacing, layer thickness, particle shape/size distribution and other build conditions. Developing process parameters for a new material is an expensive and complex optimization problem. Post-process ultrasonic NDE tests revealed that the model-based in-situ quality monitoring developed for UAM is also applicable to L-PBF Additive Manufacturing. A similar NDE set-up was designed and installed on an open-architecture L-PBF system. A layer-by-layer bond quality evaluation demonstrates the ability to detect good-quality bonds hidden behind poor-quality regions for Inconel 625 alloy. A cost-effective, process parameter development methodology has been proposed and demonstrated

Streamlining the Design and Use of Array Coils for In Vivo Magnetic Resonance Imaging of Small Animals

Small-animal models such as rodents and non-human primates play an important pre-clinical role in the study of human disease, with particular application to cancer, cardiovascular, and neuroscience models. To study these animal models, magnetic resonance imaging (MRI) is advantageous as a non-invasive technique due to its versatile contrast mechanisms, large and flexible field of view, and straightforward comparison/translation to human applications. However, signal-to-noise ratio (SNR) limits the practicality of achieving the high-resolution necessary to image the smaller features of animals in an amount of time suitable for in vivo animal MRI. In human MRI, it is standard to achieve an increase in SNR through the use of array coils; however, the design, construction, and use of array coils for animal imaging remains challenging due to copper-loss related issues from small array elements and design complexities of incorporating multiple elements and associated array hardware in a limited space. In this work, a streamlined strategy for animal coil array design, construction, and use is presented and the use for multiple animal models is demonstrated. New matching network circuits, materials, assembly techniques, body-restraining systems and integrated mechanical designs are demonstrated for streamlining high-resolution MRI of both anesthetized and awake animals. The increased SNR achieved with the arrays is shown to enable high-resolution in vivo imaging of mice and common marmosets with a reduced time for experimental setup

Study of Thickly and Thinly Sectioned Melanoma Skin Tissues with Mechanical Scanning Acoustic Reflection Microscopy

The contents of the present study are organized into two parts: the first is focused on characterizing a thickly sectioned skin tissue with a mechanical scanning acoustic reflection microscopy (hereinafter simply called “SAM”) of pulse-wave mode. The second part is focused on characterizing a thinly sectioned skin tissue with tone-burst-wave mode of SAM. We showed analyses of optical and acoustical images, as well as developed mathematical models using an angular spectrum approach for predicting contrast and characterizing acoustic properties of both sections of tissue. Also, for thin specimens a reflectance function for the tissue located on a substrate was theoretically determined, and fitted into a mathematical model of the V(z) curve. Their leaky surface acoustic wave velocities were obtained from the experimentally formed V(z) curves through FFT analyses. Finally, a computer simulation with a parameter-fitting technique was implemented to obtain the longitudinal wave velocities and densities of the tissues

Multiple parameters based pulsed eddy current non-destructive testing and evaluation

PhD ThesisEddy current sensing technique is widely used primarily because of its high tolerance to harsh environments, low cost, broad bandwidth and ease of automation. And its variant, pulsed eddy current offers richer information of target materials. However, accurate detection and characterisation of defects remains a major challenge in the petro-chemical industry using this technique which leads to spurious detection and false alarm. A number of parameters are contributory, amongst which is the inhomogeneity of the materials, coupling variation effect and relatively large lift-off effect due to coating layers. These sometimes concurrently affect the response signal. For instance, harsh and dynamic operating conditions cause variation in the electrical conductivity and magnetic permeability of materials. Also, there is the increased need to detect defects and simultaneously measure the coating layer. In practice therefore, multi-sensing modalities are employed for a comprehensive assessment which is often capital intensive. In contrast to this, multiple parameter delineation and estimation from a single transient response which is cost-effective becomes essential. The research concludes that multiple parameter delineation helps in mitigating the effect of a parameter of interest to improve the accuracy of the PEC technique for defect detection and characterisation on the one hand and for multi-parameter estimation on the other. This research, partly funded by the Petroleum Technology Development Fund (PTDF), proposes use of a novel multiple parameter based pulsed eddy current NDT technique to address the challenges posed by these factors. Numerical modelling and experimental approaches were employed. The study used a 3D finite element model to understand, predict and delineate the effect of varying EM properties of test materials on PEC response; which was experimentally validated. Also, experimental studies have been carried out to demonstrate the capabilities of the proposed to estimate multiple parameters vis-à-vis defect depth (invariant of lift-off effects) and lift-off. The major contributions of the research can be summarised thus: (1) numerical simulation to understand and separate the effect of material magnetic permeability and electrical conductivity in pulsed eddy current measurements and experimental validation; (2) proposed the lift-off point of intersection (LOI) feature for defect estimation invariant of lift-off effects for ferromagnetic and non-ferromagnetic samples; a feature which is hitherto not apparent in ferromagnetic materials (a primary material used in the oil and gas industry); (3) separation and estimation of defect and the lift-off effects in magnetic sensor based pulsed eddy current response; and (4) application of the LOI feature and demonstration of increased defect sensitivity of the PEC technique with the proposed feature in both ferrous and non-ferrous conductive materials.Petroleum Technology Development Fund (PTDF) for sponsoring this research work through the overseas scholarship scheme

Nuclear Fusion Programme: Annual Report of the Association Karlsruhe Institute of Technology (KIT)/EURATOM ; January 2010 - December 2010 (KIT Scientific Reports ; 7592)

The Karlsruhe Institute of Technology (KIT) is working in the framework of the European Fusion Programme on key technologies in the areas of superconducting magnets, microwave heating systems (Electron-Cyclotron-Resonance-Heating, ECRH), the deuterium-tritium fuel cycle, He-cooled breeding blankets, a He-cooled divertor and structural materials, as well as refractory metals for high heat flux applications including a major participation in the preparation of the international IFMIF project

The Public Service Media and Public Service Internet Manifesto

This book presents the collectively authored Public Service Media and Public Service Internet Manifesto and accompanying materials.The Internet and the media landscape are broken. The dominant commercial Internet platforms endanger democracy. They have created a communications landscape overwhelmed by surveillance, advertising, fake news, hate speech, conspiracy theories, and algorithmic politics. Commercial Internet platforms have harmed citizens, users, everyday life, and society. Democracy and digital democracy require Public Service Media. A democracy-enhancing Internet requires Public Service Media becoming Public Service Internet platforms – an Internet of the public, by the public, and for the public; an Internet that advances instead of threatens democracy and the public sphere. The Public Service Internet is based on Internet platforms operated by a variety of Public Service Media, taking the public service remit into the digital age. The Public Service Internet provides opportunities for public debate, participation, and the advancement of social cohesion. Accompanying the Manifesto are materials that informed its creation: Christian Fuchs’ report of the results of the Public Service Media/Internet Survey, the written version of Graham Murdock’s online talk on public service media today, and a summary of an ecomitee.com discussion of the Manifesto’s foundations