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1دورية أكاديمية
المؤلفون: Sotiris, Justyna O.
المصدر: Mathematics & Statistics ETDs
مصطلحات موضوعية: laser, wave propagation, turbulent atmosphere, modeling, Applied Mathematics
الوصف: The propagation of lasers through different media is a broad topic of study and falls under the larger topic of wave propagation. The focus of this thesis is the development and analysis of a numerical computational model of laser beam propagation through a turbulent atmosphere over a long distance. When a beam propagates through a turbulent atmosphere over a distance exceeding several kilometers it is a strong fluctuation propagation. There exist fewer robust methods to demonstrate how strong fluctuations affect the beam. Beam propagation can be described by the Linear Schr\"{o}dinger Equation (LSE). The fluctuations in the refractive index are mainly caused by random density fluctuations in the atmosphere and this random turbulence is described using statistical methods. In this report a numerical solution of the LSE is solved using a split-step method, and the refractive index fluctuations are accounted for by a method of random phase screens. This solution was then implemented as a computational model. The analysis of the model consists of a convergence study in the resolution of the transverse propagation screens, as well as verification of expected theoretical behaviors, including the expected spectral density of the noise screens and initial Gaussian beam form. As a result, the simulations revealed the giant fluctuations of laser intensity during propagation.
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/math_etds/156Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1156&context=math_etdsTest
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2دورية أكاديمية
المؤلفون: Gesner, Ralph Lyndon
المصدر: Electrical and Computer Engineering ETDs
مصطلحات موضوعية: Millimeter wave propagation, meteorological attenuation phenomena, Electrical and Computer Engineering
الوصف: Interest in the W & V-bands of the radio frequency (RF) spectrum has become steadily more desirable for system designers due to the ever increasing need for greater communication bandwidths and higher data rates. The 40 GHZ to 110 GHz range that constitutes the W & V-bands provide a unique solution to both of these current demands by providing a bandwidth nearly double that of all current RF frequencies in use. To date, this range has only been used for point to point satellite and short link communications meaning these bands have remained largely unexplored and undeveloped. To capitalize on the untapped benefits of these bands, research must be conducted into the nature of propagation and the effects the atmosphere imbues upon it in the form of attenuation and depolarization at such frequencies. To conduct this research and model these effects, the W & V-band Terrestrial Link Experiment (WTLE) experiment has been implemented. This experiment consists of two continuous wave beacon lens antennas located on the crest of the Sandia Mountains in Albuquerque, New Mexico. The V-band transmitter operates at a frequency of 72 GHz with a half power beam width (HPBW) of 3 degrees, a directivity of 35 dBi, and an estimated radiated isotropic power of 40 dBm. The Receiver is located 24 km away from the transmitter on the roof of the COSMIAC research center in Albuquerque, NM, and consists of two 0.5 m Cassegrain Reflectors that observe both co- and cross-polarization. In addition to the antennas, disdrometers and weather stations are located at both the receiver and transmitter locations. These stations provide atmospheric and precipitation data. Using the received power and collected atmospheric data at both locations, the atmospheric properties’ profiles along the radio path are constructed using interpolation and variation statistics between the two sites. With these profiles the attenuation due to dry air gases and the liquid water content through any present cloud can be calculated, and these two ...
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/ece_etds/474Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1500&context=ece_etdsTest
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3دورية أكاديمية
المؤلفون: Tarasenko, Nicholas Pawel
المصدر: Electrical and Computer Engineering ETDs
مصطلحات موضوعية: rain attenuation modeling at 72 ghz, propagation measurements, millimeter wave propagation, terrestrial links, drop size distributions, nexrad, Electromagnetics and Photonics
الوصف: The wireless communication sector is rapidly approaching network capacities as a direct result of increasing mobile broadband data demands. In response, the Federal Communications Commission allocated 71-76 GHz “V-band” and 81-86 GHz “W-band” for terrestrial and satellite broadcasting services. Movement by the telecommunication industry towards W/V-band operations is encumbered by a lack of validated and verified propagation models, specifically models to predict attenuation due to rain. Additionally, there is insufficient data available at W/V-bands to develop or test propagation models. The first aim of this study was the successful installation and operation of a terrestrial link to collect propagation data at W/V-band frequencies. In September 2015, the University of New Mexico, in collaboration with the Air Force Research Laboratory’s Space Vehicle Directorate, NASA’s Glenn Research Center and industry partners including (ACME, Applied Technology Associates, and Quinstar Technologies, Inc.) established the W/V-band Terrestrial Link Experiment (WTLE). WTLE was installed in the Albuquerque metro area with persistent tonal transmissions at 72 GHz and 84 GHz on a 23.5 km slanted path. The second aim of this study was the utilization of the National Weather Service’s Next Generation Weather Radar (NEXRAD) system data to statistically estimate attenuation due to rain at 72 GHz. NEXRAD data provides a distributed sense of rain rates along WTLE’s path and alleviates challenges associated with instrumenting the 23.5 km link. Furthermore, NEXRAD data alleviates the need to develop complicated routines using in-situ meteorological measurements to estimate the size of the rain cell affecting the link. Non-linear regression techniques were applied on 2017 monsoon season data to obtain rain rate power law model coefficients. Testing of these coefficients was conducted on 2018 monsoon season data with satisfactory results. The techniques employed in this analysis represent a significant advancement in the ability to ...
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/ece_etds/457Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1469&context=ece_etdsTest
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4دورية أكاديمية
المؤلفون: Ahmed, Alhassan
المصدر: Mathematics & Statistics ETDs
مصطلحات موضوعية: wave propagation, Maxwell equations, far field, Applied Mathematics
الوصف: The Maxwell equations may be viewed as evolution equations which develop an initial state of the electromagnetic field forward in time. Such evolution can be simulated numerically, that is modeled on a computer, in which case the domain of simulation is typically finite in extent. Nonetheless, one is often interested in the electromagnetic waves which reach infinity (of course which is outside of the simulation domain). Thus we are interested in near-to-far field signal propagation, that is a mathematical process where a signal or solution recorded at a finite radius r = r1 can be converted to a signal at r = r2 > r1. We achieve such a conversion via application of convolution kernels in the time-domain, although the derivation of the appropriate kernels relies on Laplace transform arguments. Decomposing the wave and Maxwell equations using scalar and vector spherical harmonics respectively, we have solved the equations on the assumption that the source and initial data are compactly supported. We further assume that we work at a large distance outside of the supports. We develop from a theoretical standpoint signal-conversion formulas for the 3d wave and Maxwell equations and these generalize the simple time delay associated with the propagation between two radii of a solution to the 1d wave equation.
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/math_etds/167Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1152&context=math_etdsTest
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5دورية أكاديمية
المؤلفون: Baker, Tyler
المصدر: Mechanical Engineering ETDs
مصطلحات موضوعية: Joints (Geology)--Mathematical models, Elastic wave propagation--Mathematical models
الوصف: Joints represent planes of discontinuity in homogeneous media. The purpose of this investigation is to model joints and determine the e\ufb00ects on waves as they propagate through joints in rock. Properties of interest include energy dissipation, energy transmission, and changes in peak stress and impulse as waves propagate through one or more joints. Rather than combining rock joints into the constitutive model of the parent rock as typically done, this research seeks to model joints discretely. By capturing the behavior of individual rock joints, discrete e\ufb00ects on wave propagation are gathered. The ability to lump multiple joints into one equivalent joint is also explored. The key result is that joints a\ufb00ect short duration pulses more than long duration pulses. A single equivalent joint transmits less energy than a set of multiple joints.
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/me_etds/55Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1054&context=me_etdsTest
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6دورية أكاديمية
المؤلفون: Martin, Lowell P.
المصدر: Mechanical Engineering ETDs
مصطلحات موضوعية: Wave Propagation, Cushioned Impact, Applied Mechanics, Mechanical Engineering
الوصف: A typical problem of wave propagation which has received substantial attention concerns the longitudinal vibrations of a long, slender, uniform elastic rod after it has been dropped on one end. The purpose of this investigation was to extend the problem to include the effect of cushioning material attached to the impacting end of a rod similar to that described above; and to conduct experiments designed to verify the analysis. This study is essentially the first step toward the analysis, by wave propagation methods, of many practical impact problems encountered in military airborne operations, experimental rocket programs, and the packaging industry.
وصف الملف: application/pdf
العلاقة: https://digitalrepository.unm.edu/me_etds/124Test; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1132&context=me_etdsTest
