Electromagnetic Acoustic Transducers (EMATs) are advanced ultrasonic transducers that generate and detect acoustic waves in an electrically conducting material without making physical contact with the material unlike its counterpart, the piezoelectric transducers (PZT). The conventional EMAT consists of copper coil that generates the dynamic field when excited with a sinusoidal current, a permanent or electromagnet that provides the bias field and the conducting material specimen. The complex interaction between the bias field and the Eddy current induced within the skin depth of the conducting material by the dynamic field gives rise to the acoustic wave that then propagates within the surface of the material. Within the research a finite element EMAT model was developed using commercial software Comsol Multiphysics, to study and compare the Eddy current density and Lorentz force density generated by three EMAT configurations: The Meander-line, Spiral and Key Type EMAT configuration respectively. It was observed that apart from the ease of fabrication and simplicity of connectivity when stacked in layers, the Key Type coil EMAT showed a high tendency to generate higher amplitude of Eddy current and Lorentz force test materials especially when stacked in layers. Also, the effect of varying some key EMAT parameters was investigated to determine the optimal performance of Key Type EMAT configuration on CS70 pipe steel plate. The research further developed a coupled finite element model using the same software, Comsol Multiphysics to account for the generation, propagation and detection of acoustic wave by the Key Type EMAT configuration on CS70 grade of pipe steel. The model can solve the magnetostatic, electrodynamic and elastic equations that give rise to acoustic wave generation, propagation and detection on the test material. The developed coupled finite element model was validated both analytically and experimentally to establish the validity of the finite element model. The analytical and experimental results obtained were consistent with the numerical result with an average discrepancy less than 9 % percent. Finally, the research developed a novel modelling strategy to decouple and quantify the various transduction forces in operation when normally-biased EMAT and magnetostrictive EMAT configurations are used on various grades of pipe steel materials. The strategy established the value of the critical excitation current beyond which acoustic wave is generated solely by the dynamic Lorentz force mechanism. The critical excitation currents when Magnetostrictive EMAT configurations are used to generate acoustic wave was found to be; 268A, 274A, 279A, 290A and 305A for CS70, L80SS, L80A, TN80Cr3 and J55 respectively. While for Normally-Biased EMAT configurations, the critical excitation current was found to be 190A, 205A, 240A, 160A and 200A respectively. This work also compared the critical excitation current of the two EMAT configurations studied and established that normally-biased EMATs are more efficient in the generation of acoustic waves than their magnetostrictive counterpart due to their lower value of critical excitation current.

No description available.

by Kwong-hon Lee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [112-115]). / Chapter CHAPTER 1. --- INTRODUCTION / Chapter CHAPTER 2. --- PRINCIPLE OF ELLIPSOMETER / Chapter CHAPTER 3. --- MATHEMATICAL REPRESENTATION OF ELLIPSOMETRY / Chapter Section 3.1 --- Ambient Substrate / Chapter Section 3.2 --- Single Layer (Ambient-film substrate) / Chapter Section 3.3 --- Multilayer system (Isotropic Stratified planar structure) / Chapter CHAPTER 4. --- CLASSIFICATION OF ELLIPSOMETER / Chapter Section 4.1 --- Null-type Ellipsometer / Chapter Section 4.2 --- Photometric Ellipsometer / Chapter Section 4.3 --- Spectroscopic Ellipsometer / Chapter CHAPTER 5. --- CONSTRUCTION AND CALIBRATION OF THE SPECTROSCOPIC ELLIPSOMETER / Chapter Section 5.1 --- Design and construction / Chapter 5.1.1 --- Optical Assembly / Chapter 5.1.2 --- Electronic Circuit / Chapter 5.1.3 --- Micro-computer (Software) / Chapter 5.1.4 --- Modification of configuration / Chapter Section 5.2 --- Alignment and Calibration / Chapter 5.2.1 --- Alignment of Optical units / Chapter 5.2.2 --- Calibration of the system / Chapter 5.2.3 --- Measurements on standard samples / Chapter CHAPTER 6. --- ANALYSIS OF ELLIPSOMETRIC PARAMETERS / Chapter Section 6.1 --- Ambient-substrate model / Chapter Section 6.2 --- Ambient-layers model / Chapter 6.2.1 --- Parameter generator / Chapter 6.2.2 --- Least square fitting / Chapter 6.2.3 --- Choice of error function / Chapter CHAPTER 7. --- EXPERIMENTAL RESULT / Chapter Section 7.1 --- Spectra of Refractive index / Chapter 7.1.1 --- Low temperature MBE growth GaAs / Chapter 7.1.2 --- Amorphous Carbon / Chapter 7.1.3 --- High order x AlxGa1-xAs with different cooling rate / Chapter Section 7.2 --- Comparison of ellipsometric spectrum of SOI samples / Chapter 7.2.1 --- Difficulty in the analysis of multi-layer structure / Chapter 7.2.2 --- Silicon on insulator (SOI) / Chapter 7.2.2.1 --- The beam current effects / Chapter 7.2.2.2 --- Annealing after implantation / Chapter CHAPTER 8. --- CONCLUSION / Chapter Section8.1 --- Summary of the results / Chapter Section8.2 --- Suggestions for future work / REFERENCE / APPENDIX(A)MARQUART ALGORITHM / Chapter (B) --- CIRCUIT DIAGRAM

by Cho, King-sum. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 108-110). / Text in English; abstracts in English and Chinese. / by Cho, King-sum. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgment --- p.iv / Contents --- p.v / List of figures --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Review of non-destructive techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Eddy current inspection --- p.2 / Chapter 1.1.3 --- Ultrasonic testing --- p.3 / Chapter 1.1.4 --- Radiography --- p.3 / Chapter 1.1.5 --- Magnetic testing methods --- p.4 / Chapter 1.2 --- Barkhausen emission --- p.4 / Chapter 1.3 --- The development of Barkhausen Emission --- p.5 / Chapter 1.4 --- The advantages of using Barkhausen emission --- p.6 / Figures for chapter1 --- p.8 / Chapter 2 --- Iron-carbon System --- p.9 / Chapter 2.1 --- Iron-iron carbide phase diagram --- p.9 / Chapter 2.2 --- Invariant reactions in the Fe-Fe3C phase diagram --- p.11 / Chapter 2.3 --- Classification of carbon steels --- p.12 / Chapter 2.4 --- Effect of heat treatment on plain-carbon steels --- p.13 / Chapter 2.4.1 --- Annealing and normalizing --- p.14 / Chapter 2.4.2 --- Slow cooling --- p.15 / Chapter 2.5 --- Process of recovery and recrystallization --- p.15 / Chapter 2.5.1 --- Recovery --- p.16 / Chapter 2.5.2 --- Recrystallization --- p.16 / Chapter 2.5.3 --- Grain growth --- p.17 / Figures for chapter2 --- p.18 / Chapter 3 --- Background Theory --- p.23 / Chapter 3.1 --- Ferromagnetism --- p.23 / Chapter 3.1.1 --- Localized moment theory --- p.24 / Chapter 3.1.2 --- Band theory --- p.25 / Chapter 3.1.3 --- Hysteresis loop --- p.25 / Chapter 3.2 --- Domain theory --- p.26 / Chapter 3.2.1 --- Magnetic domain --- p.26 / Chapter 3.2.2 --- Structure of domain wall --- p.27 / Chapter 3.2.3 --- Domain wall motion --- p.29 / Chapter 3.2.4 --- Magnetostatic energy --- p.30 / Chapter 3.2.5 --- Magnetization process --- p.32 / Chapter 3.3 --- Effect of applied stress --- p.33 / Chapter 3.3.1 --- Stress --- p.33 / Chapter 3.3.2 --- Magnetostriction --- p.34 / Chapter 3.3.3 --- Effect of stress on magnetization --- p.34 / Figures for chapter 3 --- p.37 / Chapter 4 --- Instrumentation --- p.39 / Chapter 4.1 --- Introduction --- p.39 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.39 / Chapter 4.2.1 --- Magnetizing unit --- p.40 / Chapter 4.2.2 --- Signal detection unit --- p.41 / Chapter 4.2.3 --- Signal processing unit --- p.42 / Chapter 4.3 --- The typical BE profile --- p.42 / Chapter 4.4 --- Specimen treatment --- p.43 / Chapter 4.4.1 --- Optical microscope --- p.43 / Chapter 4.4.2 --- Vickers´ة hardness tester --- p.44 / Chapter 4.4.3 --- Thermal resistance furnace --- p.45 / Chapter 4.4.4 --- Instron loading machine --- p.45 / Figures for chapter4 --- p.47 / Chapter 5 --- Experiments and Results: Evaluation of Carbon Content in Steel --- p.52 / Chapter 5.1 --- Introduction --- p.52 / Chapter 5.2 --- Experiments and results --- p.52 / Chapter 5.3 --- Discussions --- p.53 / Chapter 5.3.1 --- The magnetization process --- p.53 / Chapter 5.3.2 --- The BE profiles 、 --- p.54 / Chapter 5.3.3 --- Hardness --- p.57 / Chapter 5.4 --- Conclusions --- p.57 / Figures for chapter5 --- p.58 / Chapter 6 --- Experiments and Results: The Effects of annealing on Barkhausen Emission in Mild Steel Bars --- p.64 / Chapter 6.1 --- Introduction --- p.64 / Chapter 6.2 --- Experiments --- p.64 / Chapter 6.3 --- Results and discussions --- p.64 / Chapter 6.3.1 --- The mechanical properties --- p.65 / Chapter 6.3.2 --- Grain size --- p.65 / Chapter 6.3.3 --- BE profiles --- p.66 / Chapter 6.4 --- Conclusions --- p.67 / Figures for chapter6 --- p.68 / Chapter 7 --- Experiments and Results: The Effects of Dynamic and Residual Stresses on Barkhausen Emission in Annealed Mild Steel Bars --- p.76 / Chapter 7.1 --- Introduction --- p.76 / Chapter 7.2 --- Experiments --- p.76 / Chapter 7.2.1 --- Measurement of dynamic loading (with samples of Set A) --- p.77 / Chapter 7.2.2 --- Measurement of residual stress (with samples of Set B) --- p.77 / Chapter 7.2.3 --- Measurement of continuous tensile stress (with samples of Set C) --- p.77 / Chapter 7.3 --- Results and discussions --- p.78 / Chapter 7.3.1 --- Peak ratio of the BE profile --- p.78 / Chapter 7.3.2 --- The initial peak value under the effects of increasing tensile stress --- p.81 / Chapter 7.4 --- Conclusions --- p.82 / Figures for chapter7 --- p.83 / Chapter 8 --- Experiments and Results: The Recovery of Strained Steel Bars by Annealing --- p.94 / Chapter 8.1 --- Introduction --- p.94 / Chapter 8.2 --- Experiments --- p.94 / Chapter 8.2.1 --- Measurement of annealed sample (Set D) --- p.95 / Chapter 8.2.2 --- Results of the Set E samples --- p.95 / Chapter 8.3 --- Results and discussions --- p.95 / Chapter 8.3.1 --- Hardness --- p.96 / Chapter 8.3.2 --- Peak ratio of the BE profile --- p.97 / Chapter 8.3.3 --- BE profile for the samples of Set E --- p.98 / Chapter 8.4 --- Conclusions --- p.99 / Figures for chapter8 --- p.100 / Chapter 9 --- Conclusions and Suggestions for Further Studies --- p.104 / Bibliography --- p.108

"The CHTE surface hardening simulation tools, CarboNitrideTool© and CarbTool© have been enhanced to improve the accuracy of the simulation and to predict the microstructure and microhardness profiles after the heat treatment process. These tools can be used for the prediction of both gas and low pressure carburizing processes. The steel alloys in the data base include 10XX, 48XX, 51XX, 86XX, 93XX and Pyrowear 53. They have been used by CHTE members to design efficient carburizing cycles to maximum the profit by controlling the cost and time. In the current software, the model has successfully predicted the carbon concentration profiles for gas carburizing process and many low pressure carburizing processes. In some case, the simulation toll may not work well with the low pressure carburizing process, especially with AISI 9310 alloy. In the previous simulation, a constant carbon flux boundary condition was used. However, it has been experimentally proven that the flux is a function of time. The high carbon potential may cause soot and carbides at the outer edge. The soot and carbides will impede the diffusion of carbon during the low pressure carburizing process. The constant carbon flux cannot be appropriately used as the boundary condition. An improved model for the process is proposed. In the modeling, carbon potential and mass transfer coefficient are calculated and used as the boundary condition. CarbonitrideToolⒸ has been developed for the prediction of both carbon and nitrogen profiles for carbonitriding process. The microstructure and hardness profile is also needed by the industry. The nitrogen is an austenite stabilizer which result in high amount of retained austenite (RA). RA plays important role in the hardness. The model has been developed to predict the Martensite start temperature (Ms) which can be used for RA prediction. Mixture rule is used then to predict the hardness profiles. Experiments has been conducted to verify the simulation. The hardness profile is also predicted for tempered carburized alloys. Hollomon-Jaffe equation was used. A matrix of tempering experiments are conducted to study the Hollomon Jaffe parameter for AISI 8620 and AISI 9310 alloy. Constant C value is calculated with a new mathematical method. With the calculation result, the hardness profile can be predicted with input of tempering time and temperature. Case depth and surface hardness are important properties for carburized steel that must be well controlled. The traditional testing is usually destructive. Samples are sectioned and measured by either OES or microhardness tester. It is time consuming and can only be applied on sampled parts. The heat treating industry needs a physics based, verified simulation tool for surface hardening processes to accurately predict concentration profiles, microstructure and microhardness profiles. There is also a need for non-destructive measurement tool to accurately determine the surface hardness and case depth. Magnetic Barkhausen Noise (MBN) is one of the promising way to test the case depth and hardness. MBN measures the pulses generating by the interaction between magnetic domain walls in the ferromagnetic material and the pinning sites such as carbides, impurities and dislocation. These signals are analyzed to evaluate the properties of the carburized steel. "

by Cheng Kai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / by Cheng Kai. / Acknowledgments --- p.i / Abstract --- p.ii / Table of content --- p.iv / Chapter Chapter One --- Introduction / Chapter 1.1 --- Barkhausen emission --- p.1 / Chapter 1.2 --- Methods of measurements --- p.3 / Chapter 1.2.1 --- Magnetization of a sample --- p.4 / Chapter 1.2.2 --- Signal detection --- p.5 / Chapter 1.2.3 --- Signal processing --- p.5 / Chapter 1.3 --- Instrumentation --- p.6 / Chapter 1.3.1 --- Instron loading machine --- p.6 / Chapter 1.3.2 --- Optical microscopy --- p.7 / Chapter 1.3.3 --- Vicker's hardness tester --- p.7 / Chapter 1.3.4 --- Ceramic furnace --- p.8 / References --- p.9 / Chapter Chapter Two --- Domain Theory / Chapter 2.1 --- The postulate of domain --- p.16 / Chapter 2.2 --- Domain energy --- p.18 / Chapter 2.3 --- The magnetization process --- p.20 / Chapter 2.4 --- Effect of applied stress --- p.22 / Chapter 2.5 --- Hindrances to wall motion by inclusions --- p.23 / References --- p.24 / Chapter Chapter Three --- Steels / Chapter 3.1 --- The making of steel --- p.28 / Chapter 3.2 --- The iron-iron carbide phase diagram --- p.29 / Chapter 3.3 --- Heat treatment of plain-carbon steels --- p.29 / Chapter 3.3.1 --- Slow cooling of plain-carbon steels --- p.29 / Chapter 3.3.2 --- Rapid cooling of plain-carbon steels --- p.30 / Chapter 3.3.3 --- Annealing --- p.31 / References --- p.32 / Chapter Chapter Four --- Effects of carbon on Barkhausen emission in plain carbon steel / Chapter 4.1 --- introduction --- p.35 / Chapter 4.2 --- Experiments --- p.36 / Chapter 4.2.1 --- Samples --- p.36 / Chapter 4.3 --- Results and discussions --- p.37 / Chapter 4.4 --- Conclusions --- p.39 / References --- p.40 / Chapter Chapter Five --- Magnetization process in a steel plate/bar subjected to an increasing tensile load / Chapter 5.1 --- Introduction --- p.45 / Chapter 5.2 --- Experiments --- p.47 / Chapter 5.3 --- Results and discussions for the zinc-coated steel plate --- p.47 / Chapter 5.4 --- Results and discussions for mild steel --- p.50 / Chapter 5.5 --- A comparison between steel plate and steel bar --- p.52 / Chapter 5.6 --- Conclusions --- p.53 / References --- p.54 / Chapter Chapter Six --- Evaluation of residual stress in bent steel bars subjected to different heat treatment by Barkhausen emission / Chapter 6.1 --- Introduction --- p.60 / Chapter 6.2 --- Experiments --- p.60 / Chapter 6.3 --- Results and discussions --- p.61 / Chapter 6.4 --- Conclusions --- p.64 / References --- p.65 / Chapter Chapter Seven --- Effects of heat treatment on electrolytic zinc-coated steel plates by Barkhausen emission / Chapter 7.1 --- Introduction --- p.72 / Chapter 7.2 --- Experiments --- p.72 / Chapter 7.3 --- Results and discussions --- p.73 / Chapter 7.4 --- Conclusions --- p.75 / References --- p.76 / Chapter Chapter Eight --- Effects of demagnetizing and stray fields on Barkhausen emission / Chapter 8.1 --- Introduction --- p.80 / Chapter 8.2 --- Experiments --- p.80 / Chapter 8.3 --- Results and discussions --- p.81 / Chapter 8.4 --- Conclusions --- p.85 / References --- p.85 / Chapter Chapter Nine --- Conclusions and suggestions for further studies --- p.90

by Yu, Chak Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 129-133). / by Yu, Chak Chung. / PREFACE --- p.i / ACKNOWLEDGMENT --- p.iv / ABSTRACT --- p.v / Chapter 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Barkhausen effect --- p.2 / Chapter 1.2 --- Magnetoacoustic emission --- p.4 / Chapter 1.3 --- Methods of measurements --- p.5 / Chapter 1.3.1 --- Magnetization of a sample --- p.6 / Chapter 1.3.2 --- Signal detection --- p.8 / Chapter 1.3.3 --- Signal processing --- p.9 / Figures for chapter1 --- p.11 / References --- p.14 / Chapter 2 --- MAGNETIC PHENOMENA AND THEORIES --- p.17 / Chapter 2.1 --- Magnetostriction --- p.17 / Chapter 2.1.1 --- Spontaneous magnetostriction --- p.18 / Chapter 2.1.2 --- Saturation magnetostriction --- p.19 / Chapter 2.1.3 --- Field induced magnetostriction --- p.20 / Chapter 2.1.4 --- Magnetostriction at an angle θ to the magnetic field --- p.21 / Figures for section 21 --- p.24 / Chapter 2.2 --- Domain theory --- p.26 / Chapter 2.2.1 --- Magnetic domains --- p.26 / Chapter 2.2.2 --- Magnetostatic energy --- p.27 / Chapter 2.2.3 --- Magnetization process --- p.29 / Figures for section 22 --- p.30 / Chapter 2.3 --- Domain walls and domain processes --- p.33 / Chapter 2.3.1 --- Properties of domain walls --- p.33 / Chapter 2.3.2 --- "180° and non-180° domain walls, and closure domains" --- p.34 / Chapter 2.3.3 --- Domain wall motion --- p.35 / Chapter 2.3.4 --- Reversible and irreversible domain processes --- p.36 / Chapter 2.3.5 --- Barkhausen emission and magnetoacoustic emission --- p.38 / Figures for section 23 --- p.39 / Chapter 2.4 --- Hindrances to wall motion --- p.43 / Chapter 2.4.1 --- Residual stress --- p.43 / Chapter 2.4.1.1 --- Dislocation --- p.44 / Chapter 2.4.1.2 --- Magnetostriction --- p.45 / Chapter 2.4.1.3 --- Plastic deformation --- p.46 / Chapter 2.4.2 --- Inclusions --- p.47 / Chapter 2.4.3 --- "Domain nucleation, annihilation, and wall motion" --- p.48 / Figures for section 24 --- p.50 / References --- p.55 / Chapter 3 --- MEASUREMENT OF BARKHAUSEN EMISSION AND MAGNETOACOUSTIC EMISSION FROM A FRACTURED STEEL BAR --- p.57 / Chapter 3.1 --- Introduction --- p.57 / Chapter 3.2 --- Experiments --- p.58 / Chapter 3.3 --- Results and discussions --- p.60 / Chapter 3.3.1 --- BE and MAE profiles --- p.60 / Chapter 3.3.2 --- Defects --- p.61 / Chapter 3.3.3 --- Elongated grains --- p.62 / Chapter 3.3.4 --- Effect of annealing --- p.63 / Chapter 3.4 --- Conclusions --- p.64 / Figures and table for chapter3 --- p.66 / References --- p.70 / Chapter 4 --- NONDESTRUCTIVE INSPECTION OF A FRACTURED NICKEL BAR BY BARKHAUSEN AND MAGNETOACOUSTIC EMISSIONS --- p.71 / Chapter 4.1 --- Introduction --- p.71 / Chapter 4.2 --- Experiments --- p.72 / Chapter 4.3 --- Results --- p.73 / Chapter 4.4 --- Discussions --- p.74 / Chapter 4.4.1 --- Barkhausen emission --- p.74 / Chapter 4.4.2 --- Magnetoacoustic emission --- p.75 / Chapter 4.4.3 --- Comparison of nickel and mild steel --- p.77 / Chapter 4.5 --- Conclusions --- p.78 / Figures and table for chapter4 --- p.81 / References --- p.83 / Chapter 5 --- DETERMINATION OF THE ROLLING DIRECTION OF ELECTROLYTIC ZINC-COATED STEEL PLATE BY BARKHAUSEN EMISSION --- p.84 / Chapter 5.1 --- Introduction --- p.84 / Chapter 5.2 --- Experiments --- p.85 / Chapter 5.3 --- Results --- p.86 / Chapter 5.4 --- Discussions --- p.87 / Chapter 5.4.1 --- BE profiles 、 --- p.87 / Chapter 5.4.2 --- Effects of hardness and defects --- p.89 / Chapter 5.5 --- Conclusions --- p.90 / Figures for chapter5 --- p.91 / References --- p.97 / Chapter 6 --- MAGNETIC MEASUREMENTS MADE ON A NICKEL PLATE WITH HIDDEN HOLE --- p.98 / Chapter 6.1 --- Introduction --- p.98 / Chapter 6.2 --- Experiments --- p.99 / Chapter 6.3 --- Results and discussions --- p.100 / Chapter 6.3.1 --- Barkhausen emission --- p.100 / Chapter 6.3.2 --- Magnetoacoustic emission --- p.102 / Chapter 6.4 --- Conclusions --- p.103 / Figures for chapter6 --- p.105 / Chapter 7 --- CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDIES --- p.114 / APPENDIX --- p.118 / Chapter A1 --- Experimental setup for BE measurement --- p.118 / Chapter A2 --- Experimental setup for MAE measurement --- p.119 / Chapter A3 --- Specifications and models of the equipment used in the experiments --- p.120 / Chapter A4 --- List of figures --- p.121 / BIBLIOGRAPHY --- p.129

In recent years Terahertz (THz) time domain spectroscopy has emerged as a promising new technology with potential applications in a variety of fields, including industrial manufacturing, security screening and medical imaging. Pulsed THz systems are uniquely suited for non-destructive evaluation (NDE) of the sub-surface layers of dielectric packaging and coating materials, because they provide high dynamic range over a wide bandwidth in the far infrared portion of the electromagnetic spectrum. Often the dielectric materials of the packaging and/or surface coating layers exhibit relatively low loss and abrupt changes in the refractive index at the layer boundaries can be observed as a train of THz pulses in A-scan data. However, many practical applications of THz NDE will require fast signal acquisition to efficiently scan and evaluate many samples. The conventional processing approach shown in much of the published work in the field of THz NDE does not perform well in low signal-to-noise ratio (SNR) conditions. In addition, many samples of interest contain thin film layers and the THz pulses reflecting from the boundaries overlap on top of one another. Thus, it is not always possible to calculate the thickness of thin films from conventional time difference of arrival (TDOA) measurements. In this dissertation physics-based signal processing methods that have been historically used for radar/sonar signal processing are adapted and applied for THz NDE of layered media. Results are demonstrated with measured data from a pulsed THz system in the Northwest Electromagnetic and Acoustics Research Laboratory (NEAR-Lab) at Portland State University (PSU). This research is expected to provide an important link for THz researchers to access and apply the robust methods that have been developed over several decades for other applications. Two key contributions of this work are: 1. Development of a matched filter approach for THz NDE of thick layered media based on the maximum likelihood estimator (MLE). 2. Development of a matched field processing (MFP) approach for THz NDE of thin-film layered media, based on techniques in the underwater acoustics literature.

This thesis presents the application of ash thermography techniques to the analysis of documents. The motivation for this research is to develop the ability to non-destructively reveal covered writings in archaeological artifacts such as the Codex Selden or Egyptian car- tonnage. Current common signal processing techniques are evaluated for their effectiveness in enhancing subsurface writings found within a set of test documents. These processing techniques include: false colorization, contrast stretching, histogram equalization, median altering, Gaussian low-pass altering, layered signal reconstruction and thermal signal reconstruction (TSR), several contrast image definitions, differential absolute contrast (DAC), correlated contrast, derivative images, principal component thermography (PCT), dynamic thermal tomography (DTT), pulse phase thermography (PPT), tying-correlation analysis (FCA), Hough transform thermography (PTHTa), and transmission line matrix tying algorithm (TLMFa). New processing techniques are developed and evaluated against the existing techniques. The ability of ash thermography coupled with processing techniques to reveal subsurface writings and document strikeouts is evaluated. Flash thermography parameters are evaluated to determine most eeffective value for the document. In summary, this thesis reports the following contributions to the existing scientific knowledge: 1. A comprehensive analysis of existing pulsed thermography processing techniques. 2. New pulsed thermography processing techniques that improve upon the results of the existing techniques were developed. 3. A proof-of-concept for detecting subsurface ink writings in documents. 4. Varies the capability of pulsed thermography techniques to detect document strike- outs. 5. Demonstrates the ability to enhance surface writings based on differences in thermal characteristics when optical characteristics do not vary significantly. 6. Demonstrates that pulsed thermography significantly improves upon multi-spectral imaging for subsurface and surface writing enhancement. 7. Provides an evaluation of ash thermography parameters for the most effective document imaging.

Adhesives have presently reached a stage where they have become part of everyday life both in a professional sense as well as for household applications. They offer advantages that in many respects surpass other joining processes such as bonding of large areas, joining a wide range and dissimilar materials; and without the need for special tooling or operator training, that is often required by many other joining processes. They are of course not a panacea to all fastening applications, but they can easily be described as the most versatile and most widely used joining method at present. Engineering applications have also benefited from the advantages offered by adhesives, but they are not as liberally used due to the severe consequences that may result from bond failure. Although adhesives can demonstrate their ability to fulfil the joining strength requirements under laboratory conditions, their application in industry proved to be not as reliable as expected. A number of parameters that can easily be controlled under laboratory conditions such as temperature, humidity, surface preparation and uniform adhesive application are not as easily observed in industry. Quality assurance during manufacturing can achieve excellent results; however even in these cases the probability of having adhesive bond defects is still present. Therefore, there is a need for post process inspection of adhesive bonds where risk levels require higher reliability than what is offered though process quality control. Adhesive bond inspection is a well researched area with respectable outcomes. Non destructive inspection techniques such as x-ray, thermal, and ultrasonic are well utilised in the inspection of adhesive bonds. However, despite all the effort in this area for more than forty years, there is still no singular technique that can achieve the confidence level required in some engineering applications. Therefore, the need for continuing research in the area of non-destructive evaluation of adhesive bonds is as necessary today as it�s ever been. The research presented in this thesis, continues in the same endeavour as many other researchers; that of achieving the ultimate technique in adhesive bond inspection, capable of reaching the confidence level required for all engineering applications. The research in the thesis commenced with coverage of adhesives used for engineering applications and a study of the adhesion science that was considered necessary to enable an informed approach to the problem. Adhesive bond failure is also analysed through a literature survey as well as experimental tests on standard specimens. At the completion of the literature survey and preliminary tests, a decision was taken to follow the ultrasonic path of non-destructive testing of adhesive bonds. The reasons for this, are clearly outlined in the main body of this thesis but in summary, the literature has shown that ultrasonic evaluation is the most widely used technique by industry. Therefore, improvements on data analysis using existing techniques that exploit ultrasonic inspection have the potential to reach the widest spectrum of industrial applications. Ultrasonic inspection equipment was sourced that was capable of achieving experimental results to the accuracy level required in this research. A precision test rig was designed and constructed that was subsequently calibrated using computer based statistical techniques to ensure the validity of all results. Other ancillary equipment, such as a portable tensile testing device were also designed and constructed during the research as it became necessary. Research concentrated on techniques found to be inadequately researched in this domain. The first technique evaluated was to measure bond quality through the stress distribution in adherent and adhesive. Computer based Finite Element Analysis showed that the ability to detect variation in stress distribution at the adhesion interface is capable of revealing the local bond strength. Having found that there is no technique available at present that can measure the stress distribution at the interface, a different direction was taken that showed potential in achieving excellent quantitative results in the analysis of ultrasonic signals from adhesive bonds. This technique was rigorously evaluated and the results are systematically reported in this work.