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1مورد إلكتروني
مستخلص: 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.
الموضوعات: wave propagation
مصطلحات الفهرس: wave propagation, Maxwell equations, far field, Applied Mathematics
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2مورد إلكتروني
مستخلص: 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.
الموضوعات: wave propagation
مصطلحات الفهرس: wave propagation, Maxwell equations, far field, Applied Mathematics
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المؤلفون: Forrest, Eric G.
الموضوعات: Sensor networks., Radio wave propagation., Nuclear explosions., Réseaux de capteurs., Ondes radioélectriques Propagation., Explosions nucléaires., Nuclear explosions., Radio wave propagation., Sensor networks.
مصطلحات الفهرس: Academic Dissertation, Academic theses., Academic theses., Thèses et écrits académiques.
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عناروين إضافية: IES2008
الموضوعات: Ionosphere Congresses., Ionospheric forecasting Congresses., Ionospheric radio wave propagation Congresses., Ionosphère Congrès., Prévisions ionosphériques Congrès., Ondes radioélectriques Congrès. Propagation dans l'ionosphère, Ionosphere., Ionospheric forecasting., Ionospheric radio wave propagation.
مصطلحات الفهرس: Conference papers and proceedings.
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5مورد إلكتروني
مستخلص: 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.
الموضوعات: Wave Propagation
مصطلحات الفهرس: Wave Propagation, Cushioned Impact, Applied Mechanics, Mechanical Engineering
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6مورد إلكتروني
مستخلص: 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.
الموضوعات: Wave Propagation
مصطلحات الفهرس: Wave Propagation, Cushioned Impact, Applied Mechanics, Mechanical Engineering
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7مورد إلكتروني
الموضوعات: Electronic apparatus and appliances Periodicals., Antennas (Electronics) Periodicals., Radio wave propagation Periodicals., Antennes (Électronique) Périodiques., Ondes radioélectriques Périodiques. Propagation, Radio wave propagation., Electronic apparatus and appliances., Antennas (Electronics)
مصطلحات الفهرس: antenna arrays, communications, radar, radio astronomy, millimetre-wave, EMC, matching networks, propagation, wireless, satellite, multipath, Journals - full-text, Periodicals.
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8مورد إلكتروني
المصدر: IEEE Transactions on Antennas and Propagation vol.70 (2022) date: 2022-09-01 nr.9 p.8291-8303 [ISSN 0018-926X]
مستخلص: Human blockage and its dynamics are potential challenges for millimeter-wave (mm-wave) mobile communication. This article presents the results of wideband measurements at 27 GHz with one human blocker close by a dynamic mobile terminal (MT) as well as one or multiple dynamic human blockers further away from an MT. The measured human blockage loss is largest when the direct path (DP) in a line-of-sight (LOS) is blocked, but this loss is limited by other multipath components (MPCs). For nonline-of-sight (NLOS) channels, it is shown that human blockage loss is typically negligible. The presented measurement results show that human blockage loss in multipath channels is much smaller than that reported in diffraction-and measurement-based models, which neglect or minimize the contribution of all MPCs other than the DP. This suggests that the multipath nature of the indoor wireless channel highly limits the impact of human blockage.
مصطلحات الفهرس: Channel dynamics, Channel sounding, Delay spread, Human blockage, Indoor measurements, Millimeter-wave propagation, Path Loss, Antenna measurements, human blockage, channel sounding, Loss measurement, delay spread, Synchronization, Semiconductor device measurement, Power measurement, millimeter-wave propagation, Stairs, Delays, path loss, indoor measurements, path loss (PL), delay spread (DS), millimeter-wave (mm-wave) propagation, Tijdschriftartikel, Article
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9مورد إلكتروني
مستخلص: The Dutch infrastructure counts many bridges, the majority of which are built in concrete. These bridges have been designed and constructed according to safety codes. A lot of these bridges date from the previous century and have been designed conform outdated safety codes. Therefore, the main problem of these bridges is the uncertainty with regard to their structural health as well as their performance under the current loading conditions. The application of ‘smart aggregates’ could potentially solve these issues. Smart aggregates refer to a network of sensors that emit and receive wave signals inside the concrete structure. These sensor are embedded within the concrete and can be implemented in both new and existing structures. The changes in the medium with regard to the stresses are reflected by the phase changes of the wave signal measured by the smart aggregates. This information allows for the monitoring of the conditions of the bridge during its lifespan. The magnitude of the stress in certain parts of the structure could then indicate the need for maintenance at an early stage, thus preventing unnecessary maintenance while preserving the safety of the bridge. This method, however, requires a thorough understanding of the wave propagation inside a concrete medium subjected to a stress state. This thesis investigates how the relative wave-velocity change of a concrete-like medium is influenced by the stresses to which it is subjected. Throughout the report this relation is referred to as the acoustoelastic effect. The first part of the thesis is centered around the theoretical formulation of the acoustoelastic effect. During this study, the models of Murnaghan and Biot have been studied. Subsequently, their differences with respect to the fundamental assumptions have been indicated. Here, it has been found that the main difference between the two models is demonstrated by the way they regard the second-order deformation terms. Murnaghan assumed th
Civil Engineering | Structural Engineering | Concrete Structures -
10مورد إلكتروني
مستخلص: The Dutch infrastructure counts many bridges, the majority of which are built in concrete. These bridges have been designed and constructed according to safety codes. A lot of these bridges date from the previous century and have been designed conform outdated safety codes. Therefore, the main problem of these bridges is the uncertainty with regard to their structural health as well as their performance under the current loading conditions. The application of ‘smart aggregates’ could potentially solve these issues. Smart aggregates refer to a network of sensors that emit and receive wave signals inside the concrete structure. These sensor are embedded within the concrete and can be implemented in both new and existing structures. The changes in the medium with regard to the stresses are reflected by the phase changes of the wave signal measured by the smart aggregates. This information allows for the monitoring of the conditions of the bridge during its lifespan. The magnitude of the stress in certain parts of the structure could then indicate the need for maintenance at an early stage, thus preventing unnecessary maintenance while preserving the safety of the bridge. This method, however, requires a thorough understanding of the wave propagation inside a concrete medium subjected to a stress state. This thesis investigates how the relative wave-velocity change of a concrete-like medium is influenced by the stresses to which it is subjected. Throughout the report this relation is referred to as the acoustoelastic effect. The first part of the thesis is centered around the theoretical formulation of the acoustoelastic effect. During this study, the models of Murnaghan and Biot have been studied. Subsequently, their differences with respect to the fundamental assumptions have been indicated. Here, it has been found that the main difference between the two models is demonstrated by the way they regard the second-order deformation terms. Murnaghan assumed th
Civil Engineering | Structural Engineering | Concrete Structures
