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Digital Signal Processing Methods for Source Function Extraction of Piezoelectric ElementsKreuzinger, Tobias 19 August 2004 (has links)
Guided wave techniques have great potential for the structural
health monitoring of plate-like components. Previous research has
demonstrated the effectiveness of combining laser-ultrasonic
techniques with time-frequency representations to experimentally
develop the dispersion relationship of a plate; the high fidelity,
broad bandwidth and point-like nature of laser ultrasonics are
critical for the success of these results. Unfortunately, laser
ultrasonic techniques are time and cost intensive, and are
impractical for many in-service applications. Therefore this
research develops a complementary digital signal processing
methodology that uses mounted piezoelectric elements instead of
optical devices. This study first characterizes the spatial and
temporal effects of oil coupled and glued piezoelectric sources,
and then develops a procedure to interpret and model the
distortion caused by their limited bandwidth and finite size.
Furthermore, it outlines any inherent difficulties for time and
frequency domain considerations. The deconvolution theory for
source function extraction in the time - and frequency domain
under the presence of noise is provided and applied to measured
data. These considerations give the background for further studies
to develop a dispersion relationship of a plate with the fidelity
and bandwidth similar to results possible with laser ultrasonics,
but made using mounted piezoelectric sources.
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Spatial variability in soils: stiffness and strengthKim, Hyunki 19 July 2005 (has links)
Geotechnical properties vary in space. Statistical parameters such as mean, deviation, and correlation length are characteristics for each sediment and formation history. The effects of spatial variability on the macro-scale mechanical properties of soils are investigated using Monte Carlo non-linear finite element simulations. Boundary conditions include 1) isotropic loading, 2) zero-lateral strain loading, 3) drained and undrained deviatoric loading, and 4) small-strain wave propagation. Emphasis is placed on identifying the effects of spatial variability on the stiffness and strength of soils, recognizing emergent phenomena, and creating the background for new geotechnical design methods that take into consideration spatial variability.
The arithmetic mean of soil properties cannot be used to estimate the stiffness or strength of heterogeneous soils. Greater deviation and longer relative correlation length in the spatial distribution of soil properties yield a softer and weaker mechanical response. Load transfer concentrates along stiffer zones, leading to stress-focusing and lower K0 values. Drained loading promotes internal homogenization. Undrained deviatoric loading can cause percolation of internal weakness and shear strain localization. Spatial heterogeneity adds complexity to elastic wave propagation. Heterogeneous soil mixtures can be engineered to attain unique macroscale behavior
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Transmission strategies for wireless multi-user, multiple-input, multiple-output communication channels /Spencer, Quentin H., January 2004 (has links) (PDF)
Thesis (Ph. D.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 129-145).
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Generalized homogenization theory and inverse design of periodic electromagnetic metamaterialsLiu, Xing-Xiang 14 July 2014 (has links)
Artificial metamaterials composed of specifically designed subwavelength unit cells can support an exotic material response and present a promising future for various microwave, terahertz and optical applications. Metamaterials essentially provide the concept to microscopically manipulate light through their subwavelength inclusions, and the overall structure can be macroscopically treated as homogeneous bulk material characterized by a simple set of constitutive parameters, such as permittivity and permeability. In this dissertation, we present a complete homogenization theory applicable to one-, two- and three-dimensional metamaterials composed of nonconnected subwavelength elements. The homogenization theory provides not only deep insights to electromagnetic wave propagation among metamaterials, but also allows developing a useful and efficient analysis method for engineering metamaterials. We begin the work by proposing a general retrieval procedure to characterize arbitrary subwavelength elements in terms of a polarizability tensor. Based on this system, we may start the macroscopic analysis of metamaterials by analyzing the scattering properties of their microscopic building blocks. For one-dimensional linear arrays, we present the dispersion relations for single and parallel linear chains and study their potential use as sub-diffractive waveguides and leaky-wave antennas. For two-dimensional arrays, we interpret the metasurfaces as homogeneous surfaces and characterize their properties by a complete six-by-six tensorial effective surface susceptibility. This model also offers the possibility to derive analytical transmission and reflection coefficients for metasurfaces composed of arbitrary nonconnected inclusions with TE and TM mutual coupling. For three-dimensional metamaterials, we present a generalized theory to homogenize arrays by effective tensorial permittivity, permeability and magneto-electric coupling coefficients. This model captures comprehensive anisotropic and bianisotropic properties of metamaterials. Based on this theory, we also modify the conventional retrieval method to extract physically meaningful effective parameters of given metamaterials and fundamentally explain the common non-causality issues associated with parameter retrieval. Finally, we conceptually propose an inverse design procedure for three-dimensional metamaterials that can efficiently determine the geometry of the inclusions required to achieve the anomalous properties, such as double-negative response, in the desired frequency regime. / text
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Mobile based localisation for assisting disabled people.Samoita, Dominic Ondieki. January 2010 (has links)
M. Tech.: Electrical Engineering. / The purpose of this research was to design a low cost mobile positioning system based on Global System for Mobile communication network. The positioning system utilises Timing Advance, Signal Strength, a calibrated propagation system based on per -cell modelling and field measurements data to calculate the mobile position. Clutter and terrain features such as trees and buildings were modelled to closely represent the real environment to enhance the accuracy of the Signal Strength prediction. The key pillar of this approach is its ability to establish the contribution of each of the localised features to the propagation model. Based on the magnitude of the contribution of each feature, a conclusive correction factor for each feature was obtained. The proposed system is evaluated using field measurements collected from a Global System for Mobile communication network in diverse geographic locations in the outskirts of Pretoria. A fair correlation was established between field measurements and propagation model predictions.
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Development of a multi-measurement confined free-free resonant column device and initial studiesPucci, Martin Joseph 20 December 2010 (has links)
This study is comprised of three major parts. The first part involved the development of a multi-measurement, confined, free-free resonant column device. This device was developed to improve upon traditional manually excited, vacuum-confined, free-free methods. The device is capable of testing specimens with diameters up to 6-in., under confinements upwards of 50 psi. The device is composed of a seismic-source system, a data acquisition system and a specimen support and confinement system. The seismic source system is used to induce small-strain constrained compression waves, and longitudinal and torsional stress waves in the specimen. The data acquisition system is used to measure: (1) direct travel time of constrained compression waves, (2) longitudinal resonance in unconstrained compression, and (3) torsional resonance. From these measurements, constrained compression wave velocity, Vp, unconstrained compression wave velocity, Vc, and shear wave velocity, Vs, can be determined. With these wave velocities, small-strain, constrained modulus, Mmax, Young’s modulus, Emax, and shear modulus, Gmax can be determined. Poisson’s ratio is also calculated with the wave velocities. Finally, from the resonance measurements, small-strain material damping in unconstrained compression, DCmin, and in shear, DSmin, can be evaluated.
The second part of this study involved verification tests with materials of known dynamic properties. The tests were performed with a manufactured aluminum specimen, ASTM graded Ottawa sand, and crushed rock aggregate base. The results compared well with previous results from similar tests.
The third part of this study involved testing artificially cemented ASTM graded Ottawa sand. Cement contents (by weight) of 0.0, 0.5, 1.0 and 2.0%, were used to observe the effect of cementation with curing time at a constant confining pressure of 5 psi. The overall effect of cementation was: (1) a large increase in stiffness, and (2) an increase in material damping. The key effects related to cementation versus curing time are: (1) the increase in wave velocities are reasonably proportional to an increase in cement content up to a curing time of about 5 to 7 days, and (2) after a curing time of 5 to 7 days time the velocity increase with time seems to be similar for all cemented specimens. Additionally, the 2% cemented specimen was tested to observe the effect of confining pressure. The stiffness of this specimen was quite insensitive to confining pressure as was the material damping. / text
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ON THE RADIATION FROM SOURCES IN LAYERED MEDIA INCLUDING MAGNETOPLASMASchell, Robert Ray, 1937- January 1967 (has links)
No description available.
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A theory of the scattering of electromagnetic radiation in the troposphereShaver, Harry Nicholson, 1935- January 1958 (has links)
No description available.
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Just diagonalize: a curvelet-based approach to seismic amplitude recoveryHerrmann, Felix J., Moghaddam, Peyman P., Stolk, Christiaan C. January 2007 (has links)
No description available.
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A Two-Dimensional Horizontal Wave Propagation and Mud Mass Transport Model on Muddy Coastal RegionsOVEISY, ALI 24 July 2009 (has links)
It is well known that surface water waves interact with fluid mud on the sea bed. Wave mud interaction results in high wave energy dissipation and mud mass transport. This kind of wave energy dissipation, which generally is much more significant than wave dissipation due to bottom friction, should be considered in the simulation of wave evolution and transformation in muddy coastal environments.
In this research, a two-dimensional horizontal wave propagation and morphodynamic model for muddy coasts was developed. The model can be applied on a general three dimensional bathymetry of a soft muddy coast to calculate wave damping, fluid mud transport and resulting bathymetry change under wave action. In addition to the effect of wave-mud interaction on wave propagation, the dissipation due to wave-mud interaction was also implemented in SWAN (a third generation numerical model for Simulating WAves Nearshore) using a multilayered wave mud interaction model. These two models combined can be used for generation and propagation of waves in muddy coastal areas. The nonlinear constitutive equations of the visco-elastic-plastic model are adopted for the rheological behavior of fluid mud in this research.
The results of the numerical model are compared against a series of wave-basin experiments, wave flume experiments and field observations. Comparisons between the simulated results with the both field and laboratory data reveal the capability of the proposed model to predict the wave transformation and mud mass transport. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-07-24 11:18:18.622
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