Nenhuma / Uma das principais etapas na fabricação de combustíveis nucleares tipo placa, para a utilização em reatores de pesquisa e de propulsão naval, consiste no desenvolvimento de métodos e técnicas de ensaios não destrutivos para a avaliação do combustível nuclear durante a fabricação, assim como para análises do combustível pós-irradiação. Os ensaios não destrutivos podem contribuir para a detecção de descontinuidades durante as etapas de fabricação do combustível, como trincas e falhas na união entre o cerrne e o revestimento, que podem provocar a falha do combustível durante o seu uso em reatores nucleares. Métodos de ensaio como visual, radiográfico, correntes parasitas e ultra-som podem ser utilizados para essa finalidade. Neste trabalho foi abordado o uso do ensaio não destrutivo por ultra-som para a avaliação de combustíveis nucleares tipo placa. Devido às pequenas espessuras dos combustíveis tipo placa, assim como aos diferentes materiais presentes nos mesmos, foram utilizados, nos experimentos, transdutores ultra-sônicos de contato com sapatas de atraso e transdutores de imersão. Os ensaios foram realizados em um protótipo de combustível tipo placa constituído por um núcleo de UO2 disperso em uma matriz metálica de aço inoxidável, com revestimento em aço inoxidável. Neste protótipo foram usinados diferentes tipos de refletores artificiais, simulando a presença de descontinuidades naturais. Para os testes com os transdutores de imersão foi desenvolvido um dispositivo para a obtenção do perfil do feixe sônico emitido pelos mesmos, de forma a identificar a região de maior sensibilidade do feixe para o ensaio. Foram ainda fabricadas algumas lentes acústicas para a focalização do feixe, neste caso, sem sucesso. O uso dos diferentes tipos de transdutores ultra-sônicos possibilitou o estabelecimento de uma metodologia para a detecção de descontinuidades com diferentes geometrias e dimensões. O protótipo de combustível desenvolvido para os experimentos demonstrou ser adequado para estudos de sensibilidade do sistema de ensaio. / One of the most important steps in the fabrication processes of plate type nuclear fuels, intended to be used in research reactors or naval propulsion, is the development of nondestructive testing (NDT) methods and techniques for their quality assessment during fabrication and post-irradiation analysis. Those tests can contribute to detect discontinuities such as cracks and fails in meat-cladding junctions, that can lead to failures when installed and used in reactors. Examples of NDT methods that may be used for this purpose are visual inspection, radiography, eddy current and ultrasound. The objective of this study is to present the utilization of ultrasound methods to evaluate plate type nuclear fuels. Due to the small thicknesses of such kind of fuels, as well as the presence of different materials, the ultrasonic transducers used to perform the experiments were immersion type or contact with delay shims. Furthermore, a dummy plate fuel, constituted by a dispersion of UO2 in stainless steel matrix, with stainless steel cladding, was specially constructed. In the surface of such plate, several kinds of artificial reflectors, simulating the presence of natural flaws were machined. For immersion type ultrasonic transducers, a mechanical scanning system was developed to allow the determination of their sonic beam profiles and identification of the highest sensitivity beam region. Additionally, some acoustic lenses, useful to help on beam focalization, were fabricated and used, but the expected performance was not achieved. The use of different kinds of ultrasonic transducers allowed the establishing of a methodology to detect discontinuities of different geometry and sizes. The developed dummy fuel demonstrated to be adequate for the studies of sensitivity of the test system.

Um dos painéis derivados de madeira que tem se destacado é o OSB (Oriented Strand Board). Cada vez mais se evidencia a necessidade de novas tecnologias relacionadas à avaliação das propriedades mecânicas desse tipo de derivado de madeira, atualmente realizada através de ensaios destrutivos, efetuados horas ou dias após a respectiva produção. A utilização de métodos não-destrutivos tem se mostrado eficiente na caracterização mecânica e na avaliação da qualidade da madeira, e promissora em relação aos derivados de madeira. O objetivo geral deste trabalho foi investigar a eficiência de técnicas não-destrutivas de ensaio, de ultra-som e de stress wave, na estimativa de parâmetros físicos e mecânicos de painéis OSB fabricados no país. Foram considerados dois grupos, com 10 painéis de espessuras nominais de 15mm cada, que possuíam valores de resistência e de módulos de elasticidade na flexão estática, na direção longitudinal, distintos entre si. Primeiramente foram conduzidos os ensaios não-destrutivos, de ultra-som e de stress wave, nos painéis OSB e, em seguida, os ensaios destrutivos para a caracterização físico-mecânica e subseqüentes comparações. Os painéis estudados apresentaram valores de velocidades e constantes dinâmicas diferenciados na espessura e nas direções longitudinal e transversal. Os coeficientes de correlação obtidos entre os valores de velocidades e de constantes dinâmicas e os das propriedades físico-mecânicas, dos dois grupos de painéis, na espessura e direção transversal, não atingiram 0,70 e, na direção longitudinal superaram 0,90. Mostrou-se que é equivalente a estimativa de parâmetros mecânicos na flexão estática, ou até mesmo o estudo de painéis OSB, com a utilização dos métodos não-destrutivos de ultra-som e de stress wave. Com os resultados obtidos são gerados importantes subsídios para possibilitar a avaliação da produção de painéis OSB, viabilizando eventuais correções e ajustes até no decorrer do próprio processo produtivo. / Wood based materials production has grown in the national market, as it is the current international trend. Such products have been an interesting alternative to the sawn wood. Among them, OSB (Oriented Strand Board) has been of an outstanding importance. Its potential of production in the national context is expressive when supplying civil construction, furniture industry, and others. However, this fact also makes clear the need of innovative technologies for mechanical properties evaluation of this wood based material, since until the present day it has been conducted with destructive tests which are only made hours or days after production. Nondestructive methods utilization has been proven to be efficient for mechanical characterization and quality evaluation of sawn wood, and quite promising for wood based materials. The main goal of this research has been to investigate the efficiency of nondestructive testing (ultrasound and stress wave) when estimating physical and mechanical parameters of OSB panels made in Brazil. Two groups of ten 15mm thick panels have been used, having each one of them strength and modulus of elasticity in static bending values distinct from each other in longitudinal direction. First the two types of nondestructive testing have been conducted on all OSB panels and then destructive tests have also been conducted for physical-mechanical characterization and following comparisons. Values of velocities and dynamic constants both in thickness and longitudinal and transversal directions have been different in the two groups of studied panels. Correlation coefficients between values of velocity and dynamic constants and values of physical-mechanical properties of the two groups of panels have not reached 0,70 in thickness and transversal direction, but they have exceeded 0,90 in longitudinal direction. It has been shown that ultrasound is analogous to stress wave either when estimating static bending mechanical parameters or studying OSB panels by nondestructive testing. Such results generate some important subsidies to the evaluation of OSB production, making feasible eventual corrections and adjustments even in the course of its process.

Um dos painéis derivados de madeira que tem se destacado é o OSB (Oriented Strand Board). Cada vez mais se evidencia a necessidade de novas tecnologias relacionadas à avaliação das propriedades mecânicas desse tipo de derivado de madeira, atualmente realizada através de ensaios destrutivos, efetuados horas ou dias após a respectiva produção. A utilização de métodos não-destrutivos tem se mostrado eficiente na caracterização mecânica e na avaliação da qualidade da madeira, e promissora em relação aos derivados de madeira. O objetivo geral deste trabalho foi investigar a eficiência de técnicas não-destrutivas de ensaio, de ultra-som e de stress wave, na estimativa de parâmetros físicos e mecânicos de painéis OSB fabricados no país. Foram considerados dois grupos, com 10 painéis de espessuras nominais de 15mm cada, que possuíam valores de resistência e de módulos de elasticidade na flexão estática, na direção longitudinal, distintos entre si. Primeiramente foram conduzidos os ensaios não-destrutivos, de ultra-som e de stress wave, nos painéis OSB e, em seguida, os ensaios destrutivos para a caracterização físico-mecânica e subseqüentes comparações. Os painéis estudados apresentaram valores de velocidades e constantes dinâmicas diferenciados na espessura e nas direções longitudinal e transversal. Os coeficientes de correlação obtidos entre os valores de velocidades e de constantes dinâmicas e os das propriedades físico-mecânicas, dos dois grupos de painéis, na espessura e direção transversal, não atingiram 0,70 e, na direção longitudinal superaram 0,90. Mostrou-se que é equivalente a estimativa de parâmetros mecânicos na flexão estática, ou até mesmo o estudo de painéis OSB, com a utilização dos métodos não-destrutivos de ultra-som e de stress wave. Com os resultados obtidos são gerados importantes subsídios para possibilitar a avaliação da produção de painéis OSB, viabilizando eventuais correções e ajustes até no decorrer do próprio processo produtivo. / Wood based materials production has grown in the national market, as it is the current international trend. Such products have been an interesting alternative to the sawn wood. Among them, OSB (Oriented Strand Board) has been of an outstanding importance. Its potential of production in the national context is expressive when supplying civil construction, furniture industry, and others. However, this fact also makes clear the need of innovative technologies for mechanical properties evaluation of this wood based material, since until the present day it has been conducted with destructive tests which are only made hours or days after production. Nondestructive methods utilization has been proven to be efficient for mechanical characterization and quality evaluation of sawn wood, and quite promising for wood based materials. The main goal of this research has been to investigate the efficiency of nondestructive testing (ultrasound and stress wave) when estimating physical and mechanical parameters of OSB panels made in Brazil. Two groups of ten 15mm thick panels have been used, having each one of them strength and modulus of elasticity in static bending values distinct from each other in longitudinal direction. First the two types of nondestructive testing have been conducted on all OSB panels and then destructive tests have also been conducted for physical-mechanical characterization and following comparisons. Values of velocities and dynamic constants both in thickness and longitudinal and transversal directions have been different in the two groups of studied panels. Correlation coefficients between values of velocity and dynamic constants and values of physical-mechanical properties of the two groups of panels have not reached 0,70 in thickness and transversal direction, but they have exceeded 0,90 in longitudinal direction. It has been shown that ultrasound is analogous to stress wave either when estimating static bending mechanical parameters or studying OSB panels by nondestructive testing. Such results generate some important subsidies to the evaluation of OSB production, making feasible eventual corrections and adjustments even in the course of its process.

Two new stepped-frequency continuous wave (SFCW) radar sensor prototypes, based on a coherent super-heterodyne scheme, have been developed using Microwave Integrated Circuits (MICs) and Monolithic Millimeter-Wave Integrated Circuits (MMICs) for various surface and subsurface applications, such as profiling the surface and subsurface of pavements, detecting and localizing small buried Anti-Personnel (AP) mines and measuring the liquid level in a tank. These sensors meet the critical requirements for subsurface and surface measurements including small size, light weight, good accuracy, fine resolution and deep penetration. In addition, two novel wideband microstrip quasi-TEM horn antennae that are capable of integration with a seamless connection have also been designed. Finally, a simple signal processing algorithm, aimed to acquire the in-phase (I) and quadrature (Q) components and to compensate for the I/Q errors, was developed using LabView. The first of the two prototype sensors, named as the microwave SFCW radar sensor operating from 0.6-5.6-GHz, is primarily utilized for assessing the subsurface of pavements. The measured thicknesses of the asphalt and base layers of a pavement sample were very much in agreement with the actual data with less than 0.1-inch error. The measured results on the actual roads showed that the sensor accurately detects the 5-inch asphalt layer of the pavement with a minimal error of 0.25 inches. This sensor represents the first SFCW radar sensor operating from 0.6-5.6-GHz. The other sensor, named as the millimeter-wave SFCW radar sensor, operates in the 29.72-35.7-GHz range. Measurements were performed to verify its feasibility as a surface and sub-surface sensor. The measurement results showed that the sensor has a lateral resolution of 1 inch and a good accuracy in the vertical direction with less than  0.04-inch error. The sensor successfully detected and located AP mines of small sizes buried under the surface of sand with less than 0.75 and 0.08 inches of error in the lateral and vertical directions, respectively. In addition, it also verified that the vertical resolution is not greater than 0.75 inches. This sensor is claimed as the first Ka-band millimeter-wave SFCW radar sensor ever developed for surface and subsurface sensing applications.

Concrete structures can often be modeled as plates, for example, bridges, tunnel walls and pipes. Near-surface damage in concrete structures mostly takes the form of cracking. Surface-breaking cracks affect concrete properties and structural integrity; therefore, the nondestructive evaluation of crack depth is important for structural monitoring, strengthening and rehabilitation. On the other hand, material damping is a fundamental parameter for the dynamic analysis of material specimens and structures. Monitoring damping changes is useful for the assessment of material conditions and structural deterioration. The main objective of this research is to develop new methodologies for depth evaluation of surface-breaking cracks and the evaluation of damping in concrete plates. Nondestructive techniques based on wave propagation are useful because they are non-intrusive, efficient and cost effective. Previous studies for the depth evaluation of surface-breaking cracks in concrete have used diffracted compressional waves (P-waves). However, surface waves exhibit better properties for the characterization of near surface defects, because (a) surface waves dominate the surface response, they carry 67% of the wave propagation energy, and present lower geometrical attenuation because the propagating wave front is cylindrical; and (b) the penetration depth of Rayleigh waves (R-waves) depends on their frequency. Most of the R-wave energy concentrates at a depth of one-third of their wavelengths. The transmission of R-waves through a surface-breaking crack depends on the crack depth; this depth sensitivity is the basis for the so-called Fourier transmission coefficient (FTC) method. R-waves only exist in a half-space (one traction-free surface); whereas in the case of a plate (two traction-free surfaces), Lamb modes are generated. Fundamental Lamb modes behave like R-waves at high frequencies, because their wavelengths are small relative to the plate thickness. Lamb modes are not considered in the standard FTC method, and the FTC method is also affected by the selected spacing between receivers. The FTC calculation requires the use of an explicit time window for the identification of the arrival of surface waves, and the selection of a reliable frequency range. This research presents theoretical, numerical and experimental results. Theoretical aspects of Lamb modes are discussed, and a theoretical transfer function is derived, which can be used to study changes of Lamb modes in the time and frequency domains as a function of distance. The maximum amplitude of the wavelet transform varies with distance because of the dispersion of Lamb modes and the participation of higher Lamb modes in the response. Numerical simulations are conducted to study the wave propagation of Lamb modes through a surface-breaking crack with different depths. The surface response is found to be dominated by the fundamental Lamb mode. Using the 2D Fourier transform, the incident, transmitted and reflected fundamental Lamb modes are extracted. A transmission ratio between the transmitted and incident modes is calculated, which is sensitive to crack depths (d) normalized to the wavelength (λ) in a range (d / λ) = 0.1 to 1/3. A new wavelet transmission coefficient (WTC) method for the depth evaluation of surface-breaking cracks in concrete is proposed to overcome the main limitations of the FTC method. The WTC method gives a global coefficient that is correlated with the crack depth, which does not require time windowing and the pre-selection of a frequency bandwidth. To reduce the effects of wave reflections, which are present in the FTC method because of the non-equal spacing configuration, a new equal spacing configuration is used in the WTC method. The effects of Lamb mode dispersion are also reduced. In laboratory tests, an ultrasonic transmitter with central frequency at 50kHz is used as a source; the 50kHz frequency is appropriate for the concrete plate tested (thickness 80mm), because the fundamental Lamb modes have converged to the Rayleigh wave mode. The new method has also been used in-situ at Hanson Pipe and Precast Inc., Cambridge, Ontario, Canada, and it shows potential for practical applications. In general, the evaluation of material damping is more difficult than the measurement of wave velocity; the dynamic response and attenuation of structural vibrations are predominantly controlled by damping, and the damping is typically evaluated using the modal analysis technique, which requires considerable efforts. The existing methods based on surface waves, use the Fourier transform to measure material damping; however, an explicit time window is required for the spectral ratio method to extract the arrival of surface wave; in addition, a slope of the spectral ratio varies for different frequency ranges, and thus a reliable frequency range needs to be determined. This research uses the wavelet transform to measure material damping in plates, where neither an explicit time window nor the pre-selection of a frequency bandwidth are required. The measured material damping represents an average damping for a frequency range determined by source. Both numerical and experimental results show good agreement and the potential for practical applications.

The development of an online method for the early detection of a stator turn insulation deterioration is the objective of the research at hand. A high percentage of motor breakdowns is related to the failure of the stator insulation system. Since most of the stator insulation failures originate in the breakdown of the turn-to-turn insulation, the research in this realm is of great significance. Despite the progress that has been made in the field of stator turn fault detection methods, the most popular and the best known ones are still limited to the detection of solid turn faults. The time span between a solid turn fault and the breakdown of the primary insulation system can be as short as a few seconds. Therefore, it is desirable to develop a method capable of detecting the deterioration of the turn insulation as early as possible and prior to the development of a solid turn fault. The different stresses that cause the aging of the insulation and eventually lead to failure are described as well as the various patterns of an insulation failure. A comprehensive literature survey shows the methods presently used for the monitoring of the turn insulation. Up to now no well-tested and reliable online method that can find the deterioration of the turn insulation is available. The most commonly used turn insulation test is the surge test, which, however, is performed only when the motor is out of service and disconnected from the supply. So far no research at all has been conducted on the application of an online surge test. The research at hand examines the applicability of the surge test to an operating machine. Various topologies of online surge testing are examined with regard to their practicability and their limitations. The most practical configuration is chosen for further analysis, implementation and development. Moreover, practical challenges are presented by the non-idealities of the induction machine like the eccentricity of the rotor and the rotor slotting, and have to be taken into account. Two solutions to eliminate the influence of the rotor position on the surge waveform are presented. Even though the basic concepts of online surge testing can be validated experimentally by a machine with a solid turn fault, it is preferable to use a machine with a deteriorated turn insulation. Therefore, a method, which does not require complex and expensive hardware, to experimentally emulate the turn insulation breakdown is implemented. The concepts at any stage of the work are supported by simulations and experimental results. In addition, the theory of surge testing is further developed by giving new definitions of the test's sensitivity, i.e., the frequency sensitivity and the error area ratio (EAR) sensitivity.

Concrete structures can often be modeled as plates, for example, bridges, tunnel walls and pipes. Near-surface damage in concrete structures mostly takes the form of cracking. Surface-breaking cracks affect concrete properties and structural integrity; therefore, the nondestructive evaluation of crack depth is important for structural monitoring, strengthening and rehabilitation. On the other hand, material damping is a fundamental parameter for the dynamic analysis of material specimens and structures. Monitoring damping changes is useful for the assessment of material conditions and structural deterioration. The main objective of this research is to develop new methodologies for depth evaluation of surface-breaking cracks and the evaluation of damping in concrete plates. Nondestructive techniques based on wave propagation are useful because they are non-intrusive, efficient and cost effective. Previous studies for the depth evaluation of surface-breaking cracks in concrete have used diffracted compressional waves (P-waves). However, surface waves exhibit better properties for the characterization of near surface defects, because (a) surface waves dominate the surface response, they carry 67% of the wave propagation energy, and present lower geometrical attenuation because the propagating wave front is cylindrical; and (b) the penetration depth of Rayleigh waves (R-waves) depends on their frequency. Most of the R-wave energy concentrates at a depth of one-third of their wavelengths. The transmission of R-waves through a surface-breaking crack depends on the crack depth; this depth sensitivity is the basis for the so-called Fourier transmission coefficient (FTC) method. R-waves only exist in a half-space (one traction-free surface); whereas in the case of a plate (two traction-free surfaces), Lamb modes are generated. Fundamental Lamb modes behave like R-waves at high frequencies, because their wavelengths are small relative to the plate thickness. Lamb modes are not considered in the standard FTC method, and the FTC method is also affected by the selected spacing between receivers. The FTC calculation requires the use of an explicit time window for the identification of the arrival of surface waves, and the selection of a reliable frequency range. This research presents theoretical, numerical and experimental results. Theoretical aspects of Lamb modes are discussed, and a theoretical transfer function is derived, which can be used to study changes of Lamb modes in the time and frequency domains as a function of distance. The maximum amplitude of the wavelet transform varies with distance because of the dispersion of Lamb modes and the participation of higher Lamb modes in the response. Numerical simulations are conducted to study the wave propagation of Lamb modes through a surface-breaking crack with different depths. The surface response is found to be dominated by the fundamental Lamb mode. Using the 2D Fourier transform, the incident, transmitted and reflected fundamental Lamb modes are extracted. A transmission ratio between the transmitted and incident modes is calculated, which is sensitive to crack depths (d) normalized to the wavelength (λ) in a range (d / λ) = 0.1 to 1/3. A new wavelet transmission coefficient (WTC) method for the depth evaluation of surface-breaking cracks in concrete is proposed to overcome the main limitations of the FTC method. The WTC method gives a global coefficient that is correlated with the crack depth, which does not require time windowing and the pre-selection of a frequency bandwidth. To reduce the effects of wave reflections, which are present in the FTC method because of the non-equal spacing configuration, a new equal spacing configuration is used in the WTC method. The effects of Lamb mode dispersion are also reduced. In laboratory tests, an ultrasonic transmitter with central frequency at 50kHz is used as a source; the 50kHz frequency is appropriate for the concrete plate tested (thickness 80mm), because the fundamental Lamb modes have converged to the Rayleigh wave mode. The new method has also been used in-situ at Hanson Pipe and Precast Inc., Cambridge, Ontario, Canada, and it shows potential for practical applications. In general, the evaluation of material damping is more difficult than the measurement of wave velocity; the dynamic response and attenuation of structural vibrations are predominantly controlled by damping, and the damping is typically evaluated using the modal analysis technique, which requires considerable efforts. The existing methods based on surface waves, use the Fourier transform to measure material damping; however, an explicit time window is required for the spectral ratio method to extract the arrival of surface wave; in addition, a slope of the spectral ratio varies for different frequency ranges, and thus a reliable frequency range needs to be determined. This research uses the wavelet transform to measure material damping in plates, where neither an explicit time window nor the pre-selection of a frequency bandwidth are required. The measured material damping represents an average damping for a frequency range determined by source. Both numerical and experimental results show good agreement and the potential for practical applications.

The quantitative nondestructive evaluation (NDE) of cement-based materials is a critical area of research that is leading to advances in the health monitoring and condition assessment of the civil infrastructure. Ultrasonic NDE has been implemented with varying levels of success to characterize cement-based materials with complex microstructure and damage. A major issue with the application of ultrasonic techniques to characterize cement-based materials is their inherent inhomogeneity at multiple length scales. Ultrasonic waves propagating in these materials exhibit a high degree of attenuation losses, making quantitative interpretations difficult. Physically, these attenuation losses are a combination of internal friction in a viscoelastic material (ultrasonic absorption), and the scattering losses due to the material heterogeneity. The objective of this research is to use ultrasonic attenuation to characterize the microstructure of heterogeneous cement-based materials. The study considers a real, but simplified cement-based material, cement paste - a common bonding matrix of all cement-based composites. Cement paste consists of Portland cement and water but does not include aggregates. First, this research presents the findings of a theoretical study that uses a set of existing acoustics models to quantify the scattered ultrasonic wavefield from a known distribution of entrained air voids. These attenuation results are then coupled with experimental measurements to develop an inversion procedure that directly predicts the size and volume fraction of entrained air voids in a cement paste specimen. Optical studies verify the accuracy of the proposed inversion scheme. These results demonstrate the effectiveness of using attenuation to measure the average size, volume fraction of entrained air voids and the existence of additional larger entrapped air voids in hardened cement paste. Finally, coherent and diffuse ultrasonic waves are used to develop a direct relationship between attenuation and water to cement (w/c) ratio. A phenomenological model based on the existence of fluid-filled capillary voids is used to help explain the experimentally observed behavior. Overall this research shows the potential of using ultrasonic attenuation to quantitatively characterize cement paste. The absorption and scattering losses can be related to the individual microstructural elements of hardened cement paste. By taking a fundamental, mechanics-based approach, it should be possible to add additional components such as scattering by aggregates or even microcracks in a systematic fashion and eventually build a realistic model for ultrasonic wave propagation study for concrete.

Two new stepped-frequency continuous wave (SFCW) radar sensor prototypes, based on a coherent super-heterodyne scheme, have been developed using Microwave Integrated Circuits (MICs) and Monolithic Millimeter-Wave Integrated Circuits (MMICs) for various surface and subsurface applications, such as profiling the surface and subsurface of pavements, detecting and localizing small buried Anti-Personnel (AP) mines and measuring the liquid level in a tank. These sensors meet the critical requirements for subsurface and surface measurements including small size, light weight, good accuracy, fine resolution and deep penetration. In addition, two novel wideband microstrip quasi-TEM horn antennae that are capable of integration with a seamless connection have also been designed. Finally, a simple signal processing algorithm, aimed to acquire the in-phase (I) and quadrature (Q) components and to compensate for the I/Q errors, was developed using LabView. The first of the two prototype sensors, named as the microwave SFCW radar sensor operating from 0.6-5.6-GHz, is primarily utilized for assessing the subsurface of pavements. The measured thicknesses of the asphalt and base layers of a pavement sample were very much in agreement with the actual data with less than 0.1-inch error. The measured results on the actual roads showed that the sensor accurately detects the 5-inch asphalt layer of the pavement with a minimal error of 0.25 inches. This sensor represents the first SFCW radar sensor operating from 0.6-5.6-GHz. The other sensor, named as the millimeter-wave SFCW radar sensor, operates in the 29.72-35.7-GHz range. Measurements were performed to verify its feasibility as a surface and sub-surface sensor. The measurement results showed that the sensor has a lateral resolution of 1 inch and a good accuracy in the vertical direction with less than  0.04-inch error. The sensor successfully detected and located AP mines of small sizes buried under the surface of sand with less than 0.75 and 0.08 inches of error in the lateral and vertical directions, respectively. In addition, it also verified that the vertical resolution is not greater than 0.75 inches. This sensor is claimed as the first Ka-band millimeter-wave SFCW radar sensor ever developed for surface and subsurface sensing applications.

This thesis investigates the generation of second harmonic bulk waves in the presence of a free boundary. Second harmonic waves have proven to be useful in the field of nondestructive evaluation to detect fatigue in a material at an early stage. Since most experimental setups include a free surface, the influence of such a boundary is of significant practical interest. As a result, the objective of this research is to develop a quantitative understanding of the complete process of second harmonic generation at a free boundary. This research shows that the interaction of primary waves (with each other) in the nonlinear framework leads to the generation of second harmonic bulk waves. We distinguish between self-interaction of a single primary wave and the cross-interaction of two different primary waves. The proposed approach uses the perturbation method to solve the nonlinear equations of motion, and shows two fundamentally different solutions. In the case of resonance, the secondary waves grow with propagation distance. This is the most important practical case, since the growing amplitudes of these waves should be easier to experimentally measure. In the second, non-resonant case, the amplitudes of the secondary waves are constant. The complete process of second harmonic generation is analyzed for an incident Pand an incident SV-wave, with the primary and secondary fields given. Finally, the degenerate case of normal incidence is presented. Normal and oblique incidence are compared with regard to their feasibility in experimental setups. The specific behavior of second harmonic waves propagating in aluminum is numerically determined. These results enable a variety of physical insights and conclusions to be drawn from the analytical and numerical investigations.