Lying between the microwave and far infrared (IR) regions, the "terahertz gap" is a relatively unexplored frequency band in the electromagnetic spectrum that exhibits a unique combination of properties from its neighbors. Like in IR, many materials have characteristic absorption spectra in the terahertz (THz) band, facilitating the spectroscopic "fingerprinting" of compounds such as drugs and explosives. In addition, non-polar dielectric materials such as clothing, paper, and plastic are transparent to THz, just as they are to microwaves and millimeter waves. These factors, combined with sub-millimeter wavelengths and non-ionizing energy levels, makes sensing in the THz band uniquely suited for many NDE applications. In a typical nondestructive test, the objective is to detect a feature of interest within the object and provide an accurate estimate of some geometrical property of the feature. Notable examples include the thickness of a pharmaceutical tablet coating layer or the 3D location, size, and shape of a flaw or defect in an integrated circuit. While the material properties of the object under test are often tightly controlled and are generally known a priori, many objects of interest exhibit irregular surface topographies such as varying degrees of curvature over the extent of their surfaces. Common THz pulsed imaging (TPI) methods originally developed for objects with planar surfaces have been adapted for objects with curved surfaces through use of mechanical scanning procedures in which measurements are taken at normal incidence over the extent of the surface. While effective, these methods often require expensive robotic arm assemblies, the cost and complexity of which would likely be prohibitive should a large volume of tests be needed to be carried out on a production line. This work presents a robust and efficient physics-based image processing approach based on the mature field of parabolic equation methods, common to undersea acoustics, seismology, and other areas of science and engineering. The method allows the generation of accurate 3D THz tomographic images of objects with irregular, non-planar surfaces using a simple planar scan geometry, thereby facilitating the integration of 3D THz imaging into mainstream NDE use.

The aim of this research is to assess the material properties of concrete like modulus of elasticity, compressive strength, and Poisson’s ratio using various nondestructive Testing (NDT) methods like Ultrasonic Pulse Velocity (UPV) and Rebound Hammer (RH). Assessment of material properties of concrete is very important as they are used for structural design process. Various NDT methods are applied to ensure the quality of concrete specimens but they can also be used to find material properties. UPV is a NDT method which is used to test the internal condition of the concrete specimen. RH is a surface hardness testing method and can be used to test the homogeneity of the specimen. For this study, several batches of concrete samples with three different design strengths of 6000 psi, 8000 psi, and 12000 psi were casted. Modulus of elasticity and Poisson’s ratio were calculated from UPV P-wave and S-wave velocities. A Nomogram was developed by combining the longitudinal ultrasonic pulse velocities, rebound numbers, and compressive strengths measured from UPV, RH, and compressive strength tests respectively. This combined NDT correlation curve (Nomogram) can be used to estimate compressive strength of concrete if UPV and rebound values are known. The accuracy of these NDT methods were determined by comparing estimated strength to the actual strength. Furthermore, the effect of moisture content on UPV and rebound values was reviewed and also studied dynamic modulus of elasticity and its relation with static modulus of elasticity of the concrete was investigated for better understanding.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / Includes bibliographical references. / by Tomas A. Gonzalez. / Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980.

Em formação de imagens por ultrassom de objetos com superfícies curvas, em imersão, se as velocidades de propagação no ruído e no objeto forem muito diferentes os efeitos de refração precisam ser compensados. Nesse caso a posição e a forma da superfície precisam ser conhecidas. Neste trabalho a superfície é detectada pelo mesmo array linear que captura os sinais para a formação de imagem.Dois métodos rápidos de detecção de superfície foram propostos, um baseado em técnicas de formação de imagem e outro que utiliza informações de tempo de percurso de ecos extraídas diretamente dos sinais de ultrassom.Os dois métodos foram comparados,e o método baseado em imagem apresentou uma maior tolerância a erros nos sinais, enquanto o método baseado em tempo de percurso mostrou-se mais rápido.Com a superfície detectada, a imagem foi formada por combinação de imagens por abertura sintética, que apresentou uma boa resolução. O uso conjunto dos métodos de detecção de superfície propostos e da formação de imagem resultou em uma taxa de imagens que permite ensaios interativos,com processamento em uma CPU de uso geral. / In ultrasound imaging ofobjects with curved surface, in immersion, the refraction eects must be compensated for if the propagation speed in the uid is very dierent from the speed in the object. In this case the surface position and shape must be known. In this work the surface is detected by the same linear array that captures the signals for the image formation. Two fast methods for surface detection were proposed,one is based on image formation techniques and another utilizes the echotime-of-ight information directly from the ultra\\sound signals.The two methods were compared,and the image-based method was more tolerant of signal errors, while the time-of-ight-based method was faster. After the surface detection, the image was formed by combination of synthetic aperture images,with a good resulting resolution. The utilization of the proposed surface detection methods together with the image formation resulted in an image rate that allows interactive testing, with processing on a general-purpose CPU.

In recent decades techniques related to the measurement of elastic waves have advanced significantly. It is now possible with relatively inexpensive equipment to record amplitudes and frequency bands that were unthinkable two decades ago. This has led to the development of theoretical topics which application was questionable until not long ago, to profit from new technological potential in obtaining more and better experimental information. In this context the study of the propagation of guided waves in solids is presented as a knowledge that allows to detect damage with efficiency and economy in a number of structures in which at least one dimension is much larger than the other two. This is the case for rails, tubulations and pressure vessels among others. In this work, guided waves propagation characteristics are studied, first in a prismatic bar and then within the geometry of a rail. In both cases, dispersion curves were computed according two different work methodologies, first using an axisymmetric model and then corroborated with a model of periodic conditions. Finally propagation of a Tone-Burst waves were simulated on the analyzed geometries, leading to the discussion of how the waves scatter along its propagation. The results obtained were the dispersion curves of both sections. / En las últimas décadas técnicas relacionadas con la medición de ondas elásticas han avanzado sensiblemente. Actualmente, con equipamientos relativamente económicos es posible registrar amplitudes y franjas de frecuencia que eran impensables dos décadas atrás. Este hecho ha motivado que tópicos teóricos que hasta hace un tiempo tenían una aplicación cuestionable tengan que ser desarrollados para poder aprovechar las nuevas potencialidades tecnológicas en la obtención de mayor y mejor información experimental. En este contexto, el estudio de la propagación de ondas guiadas en sólidos se presenta como un conocimiento que posibilita detectar daño con eficiencia y economía en una serie de estructuras en las cuales por lo menos una dimensión es mucho mayor que las otras dos. Es el caso de estructuras tubulares, rieles o recipientes sometidos a presión entre otras. En el presente trabajo se estudian las características de propagación de ondas guiadas primeramente una barra rectangular y posteriormente en la geometría de un riel. En ambos casos, fueron calculadas las curvas de dispersión obtenidas con por dos metodologías de trabajo por elementos finitos, la primer metodología fue emplear un cálculo aplicando un modelo axisimétrico, y luego corroborado con un modelo de condiciones periódicas y posteriormente fue simulada la propagación de una onda tipo Toneburst sobre las geometrías analizadas discutiendo cómo dicha onda se dispersa durante su propagación. Los resultados obtenidos fueron las curvas de dispersión de ambas secciones.

Os ensaios não destrutivos servem como uma importante ferramenta para a análise de estruturas de concreto armado. A utilização de ensaios de velocidade de propagação do pulso ultra-sônico (VPU) permite realizar um acompanhamento das características do material ao longo de sua vida útil. Através da análise dos dados obtidos, pode-se averiguar a uniformidade do concreto, controlar a sua qualidade, acompanhar sua deterioração e, através de comparação com corpos de prova de referência e, até mesmo, estimar a resistência do mesmo. No entanto, as técnicas atuais para análise dos resultados coletados são, em grande parte, baseadas na sensibilidade dos profissionais que as aplicam. Para facilitar o controle e inspeção de estruturas de concreto armado é fundamental desenvolver estratégias para tornar esta análise mais simples e precisa. Este trabalho se baseia na hipótese de que a aplicação de Redes Neurais Artificiais (RNAs) pode gerar modelos de relacionamento úteis e acurados entre as características do concreto, sua compacidade e sua resistência à compressão. O intuito é determinar se com o uso de RNAs é possível estabelecer relações não-lineares que permitam estimar a resistência do concreto a partir do conhecimento de algumas propriedades básicas e da verificação da sua compacidade por meio de ensaios de VPU. Os resultados indicam que as RNAs podem ser usadas para gerar métodos numéricos robustos e flexíveis para estimativa da resistência à compressão a partir de dados de VPU. O estudo evidencia uma considerável melhora nos resultados de estimação da resistência quando se empregam modelos neurais, em comparação a modelos estatísticos tradicionais. Para os dados coletados, provenientes de diversas pesquisas, os modelos tradicionais geram estimativas com coeficientes de determinação que não ultrapassam um valor de R² de 0,40. Já as redes neurais conseguem ajustes com R² da ordem de 0,90. Além de contribuir para uma melhor análise de situações em que haja dúvidas sobre a resistência ou homogeneidade de elementos de concreto, o trabalho demonstra que modelos neurais são uma forma eficiente de ordenar e transferir conhecimento não estruturado. Constatou-se, ainda, que, dada sua capacidade de aprendizagem e de generalização do conhecimento adquirido, as RNAs se constituem em um meio rápido e preciso para modelagem de fenômenos complexos. / Nondestructive Testing (NDT) techniques are useful tools for analyzing reinforced concrete (RC) structures. The use of Ultrassonic Pulse Velocity (UPV) measurements enables the monitoring of changes in some critical characteristics of concrete over the service life of a structure. The interpretation of the data collected allows an assessment of concrete uniformity, and can be used to perform quality control, to monitor deterioration and even, by means of comparison against reference samples, to estimate compressive strength. Nonetheless, the current techniques for UPV data analysis are, on a large degree, based on the sensitivity of the professionals who apply these tests. For accurate diagnosis it is necessary to consider the various factors and conditions that can affect the results. To proper control and inspect RC facilities it is essential to develop appropriate strategies to make the task of data interpretation easier and more accurate. This work is based on the notion that using Artificial Neural Networks (ANNs) is a feasible way to generate workable estimation models correlating concrete characteristics, compacity and compressive strength. The goal is to determine if it is possible to establish models based on non-linear relationships that are capable of estimating with good accuracy the concrete strength based on previous knowledge of some basic material characteristics and UPV measurements. The study shows that this goal is achievable and indicates that neural models perform better than traditional statistical models. For the data collected in this work, provided by various researchers, traditional regression models cannot exceed R² = 0.40, while the use of ANNs allows the creation of models that can reach a determination coefficient R² = 0.90. The results make clear that, besides contributing to better the analysis of situations where there is doubts regarding concrete strength or uniformity, neural models are an efficient way to order and transfer unstructured knowledge. It was shown that, given the learning capacity and its ability to generalize acquired information into mathematical patterns, ANNs are a quick and adequate way to model complex phenomena.

by Ng, Hiu Tung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 121-123). / by Ng, Hiu Tung. / Acknowledgement --- p.i / Abstract --- p.ii / Table of Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xi / Chapter Chapter One --- Introduction --- p.1 / Chapter 1.1 --- Non-destructive testing techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Electrical methods (Eddy current testing) --- p.3 / Chapter 1.1.3 --- Ultrasonic testing --- p.4 / Chapter 1.1.4 --- Radiography --- p.5 / Chapter 1.1.5 --- Magnetic methods --- p.6 / Chapter 1.2 --- The development of Barkhausen and magnetoacoustic emissions --- p.7 / Chapter 1.2.1 --- Barkhausen emission --- p.7 / Chapter 1.2.2 --- Magnetoacoustic emission --- p.8 / Chapter 1.3 --- The advantages of using Barkhausen and magnetoacoustic emission over the other nondestructive techniques --- p.10 / Chapter Chapter Two --- Fundamental concept in ferromagnetic materials --- p.12 / Chapter 2.1 --- Ferromagnetism --- p.12 / Chapter 2.1.1 --- Curie point --- p.13 / Chapter 2.1.2 --- Hysteresis loop --- p.14 / Chapter 2.2 --- Magnetic domains --- p.17 / Chapter 2.2.1 --- Magneto static energy --- p.17 / Chapter 2.2.2 --- Structure of domain wall --- p.19 / Chapter 2.2.3 --- Domain wall motion --- p.21 / Chapter 2.2.4 --- Domain nucleation --- p.22 / Chapter 2.3 --- Magnetostriction --- p.28 / Chapter 2.3.1 --- Spontaneous magnetostriction --- p.28 / Chapter 2.3.2 --- Saturation magnetostriction --- p.29 / Chapter 2.3.3 --- Field-induced magnetostriction --- p.29 / Chapter 2.3.4 --- Magnetostriction of polycrystalline --- p.30 / Chapter 2.4 --- Effect of stress on magnetic properties --- p.36 / Chapter 2.4.1 --- Stress --- p.36 / Chapter 2.4.2 --- Effect of stress on the magnetization --- p.37 / Chapter 2.4.3 --- Effect of stress on the magnetostriction --- p.38 / Chapter 2.5 --- Eddy current shielding --- p.41 / Chapter Chapter Three --- Barkhausen emission and magnetoacoustic emission --- p.42 / Chapter 3.1 --- Barkhausen emission --- p.42 / Chapter 3.1.1 --- The wall potential energy model of Barkhausen emission --- p.43 / Chapter 3.1.2 --- Typical BE profiles --- p.45 / Chapter 3.2 --- Magnetoacoustic emission --- p.48 / Chapter 3.2.1 --- Magnetoacoustic emission model --- p.48 / Chapter 3.2.2 --- Typical MAE profiles --- p.50 / Chapter Chapter Four --- Instrumentation --- p.52 / Chapter 4.1 --- Introduction --- p.52 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.53 / Chapter 4.3 --- Experimental setup for magnetoacoustic emission --- p.56 / Chapter 4.4 --- Specimen treatment --- p.58 / Chapter 4.4.1 --- Furnace --- p.58 / Chapter 4.4.2 --- Instron loading machine --- p.60 / Chapter 4.4.3 --- Optical microscopy --- p.60 / Chapter 4.4.4 --- Vicker's hardness tester --- p.61 / Chapter Chapter Five --- Effect of field frequency and strength on Barkhausen emission in mild steel and nickel --- p.66 / Chapter 5.1 --- Introduction --- p.66 / Chapter 5.2 --- Experiments --- p.67 / Chapter 5.3 --- Results and discussions --- p.68 / Chapter 5.4 --- Conclusions --- p.76 / Chapter Chapter Six --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in steel bar --- p.77 / Chapter 6.1 --- Introduction --- p.77 / Chapter 6.2 --- Experiments --- p.81 / Chapter 6.3 --- Results and discussions --- p.84 / Chapter 6.3.1 --- BE profiles --- p.84 / Chapter 6.3.2 --- MAE profiles --- p.85 / Chapter 6.3.3 --- Optical microscopy and hardness measurements --- p.85 / Chapter 6.4 --- Conclusions --- p.92 / Chapter Chapter Seven --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in a nickel bar --- p.93 / Chapter 7.1 --- Introduction --- p.93 / Chapter 7.2 --- Experiments --- p.96 / Chapter 7.3 --- Results and discussions --- p.97 / Chapter 7.3.1 --- Hardness and optical microscopy measurement --- p.97 / Chapter 7.3.2 --- BE profiles --- p.98 / Chapter 7.3.3 --- MAE profiles --- p.99 / Chapter 7.4 --- Comparison of nickel and mild steel --- p.106 / Chapter 7.5 --- Conclusions --- p.108 / Chapter Chapter Eight --- Effect of dynamic stress on Barkhausen emission in mild steel --- p.109 / Chapter 8.1 --- Introduction --- p.109 / Chapter 8.2 --- Experiments --- p.110 / Chapter 8.3 --- Results and discussions --- p.112 / Chapter 8.4 --- Conclusions --- p.118 / Chapter Chapter Nine --- Conclusions --- p.119 / References --- p.121

Adhesion, heterogeneous catalysis, electrochemistry, and many other important processes and properties are driven by interactions at surfaces and interfaces. Vibrational sum frequency generation spectroscopy (VSFG) is an increasingly popular analytical technique because it can provide information about the nature and physical orientation of functional groups at these surfaces and interfaces. Analysis of VSFG data can be complicated by the presence of SFG signal that is not associated with a resonant vibration. This nonresonant sum frequency generation (NR-SFG) signal can interfere with the resonant signal and influence the detected spectrum. Methods have been developed to remove NR-SFG signal; however, these methods tend to be complicated and expensive. In fact many SFG practitioners do not have the ability to remove NR-SFG signal components, and systems designed to remove NR-SFG signal contributions may not be able to do so for some materials. We have worked to help develop a better understanding of NR-SFG. As part of this work, a better understanding of the temporal and phase behavior of NR-SFG signal has been developed, based on the behavior of NR-SFG signal from Si(111) wafers. This work calls into question some assumptions underlying nonresonant suppression methods based on time-domain detection. A new method for nondestructively testing (NDT) materials has been developed that uses nonresonant second harmonic generation, the degenerate form of SFG. This new NDT technology has the potential to detect several forms of material damage, such as aluminum sensitization, and plastic deformation of materials, which are largely invisible to current NDT technologies. Methods for extracting functional group orientation from VSFG data that contains NR-SFG contributions are also demonstrated and used to investigate how the surface of high density polyethylene changes in response to mechanical deformation. This work shows that the inability to remove NR-SFG contributions from VSFG spectra does not mean that these instruments cannot be used to make important discoveries. It simply means that NR-SFG contributions must be properly understood and accounted for during experimental design, and kept in mind during the analysis of VSFG spectra.

Terahertz (THz) wavelengths have attracted recent interest in multiple disciplines within engineering and science. Situated between the infrared and the microwave region of the electromagnetic spectrum, THz energy can propagate through non-polar materials such as clothing or packaging layers. Moreover, many chemical compounds, including explosives and many drugs, reveal strong absorption signatures in the THz range. For these reasons, THz wavelengths have great potential for non-destructive evaluation and explosive detection. Three-dimensional (3-D) reflection imaging with considerable depth resolution is also possible using pulsed THz systems. While THz imaging (especially 3-D) systems typically operate in transmission mode, reflection offers the most practical configuration for standoff detection, especially for objects with high water content (like human tissue) which are opaque at THz frequencies. In this research, reflection-based THz synthetic-aperture (SA) imaging is investigated as a potential imaging solution. THz SA imaging results presented in this dissertation are unique in that a 2-D planar synthetic array was used to generate a 3-D image without relying on a narrow time-window for depth isolation [1]. Novel THz chemical detection techniques are developed and combined with broadband THz SA capabilities to provide concurrent 3-D spectral imaging. All algorithms are tested with various objects and pressed pellets using a pulsed THz time-domain system in the Northwest Electromagnetics and Acoustics Research Laboratory (NEAR-Lab).

Abstract not available