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1
Liu, Zhongjian. "Investigation of low frequency electromagnetic waves for long-range lightning location." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760951.
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Lightning is the strongest natural electromagnetic radiation source, emitting electromagnetic energy in the frequency range from ~4 Hz to ~300 MHz or more. The location of lightning is calculated based on the received electromagnetic waves. The received electromagnetic waves, or lightning sferics, propagate from the lightning radiation source to the receiver along the ground path and reflections by the ionosphere named sky waves. Particularly for a long-baseline (>400 km) lightning receiver array, the received electromagnetic waves are usually a mixture of the ground wave and sky waves, which easily introduce a certain level of location uncertainty. Lightning sferics and the wave propagation velocity are analysed in order to mitigate the interference from long distance wave propagation. The complex lightning sferics are calculated by the Hilbert transform, which provides additional information regarding the instantaneous phase and frequency. The time differences calculated from the instantaneous phases are closer to the phase delay time introduced by the speed of light when compared to other possible signal processing methods. It is also found that the instantaneous frequencies at maximum amplitudes in the waveform bank are distance dependent, which has a potential application, i.e., to determine the distance between the lightning location and the receiver. The radio waves from two submarine communication transmitters at 20.9 kHz and 23.4 kHz exhibit phase propagation velocities that are ~0.51% slower and ~0.64% faster than the speed of light as a result of sky wave contributions and ground effects. Therefore, a novel technique with a variable phase propagation velocity is implemented for the first time using arrival time differences. The lightning locations inferred from variable velocities improve the accuracy of locations inferred from a fixed velocity by ~0.89–1.06 km when compared to the lightning locations reported by the UK MetOffice. The velocity map inferred from the calculated phase propagation velocities reflects the impact of sky waves and ground effects on the calculation of lightning locations as a result of the network configuration. Overall, the wave propagation issues are mitigated by analysis of the complex waveform and the variable phase propagation velocity. Finally, three interferometric methods, 2D lightning mapping, cross-correlation with a short time window, and lightning locations inferred from each sample, are proposed here in order to take advantage of the greater number of samples and information from the recordings.
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Seguin, Sarah Ann. "Detection of low cost radio frequency receivers based on their unintended electromagnetic emissions and an active stimulation." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Seguin_09007dcc80708216.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.<br>Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 23, 2009) Includes bibliographical references.
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Umeda, Takayuki. "Generation of low-frequency electrostatic and electromagnetic waves as nonlinear consequences of beam–plasma interactions." American Institite of Physics, 2008. http://hdl.handle.net/2237/12028.
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Chen, Chi-Chih. "Design and applications of two low frequency guided wave electromagnetic measurement structures." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406708013.
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Pokkuluri, Kiran S. "Effect of Admixtures, Chlorides, and Moisture on Dielectric Properties of Portland Cement Concrete in the Low Microwave Frequency Range." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/37039.
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The use of electromagnetic waves as a nondestructive
evaluation technique to evaluate Portland cement concrete
(PCC) structures is based on the principle that a change in
the structure, composition, or properties of PCC results in
a change in its dielectric properties. The coaxial
transmission line is one of the few devices that can
measure the dielectric properties of PCC at a frequency
range of 100-1000 MHz. A coaxial transmission line
developed at Virginia Tech was used to study the effect
of moisture, type of aggregate, water/cement ratio, curing
period, admixture type (microsilica, superplasticizer, and
shrinkage admixture), and chloride content on the dielectric
properties of PCC.
Measurements were conducted in the time
domain and converted to the frequency domain using Fast
Fourier Transform. The research found that an increase in
the moisture content of PCC resulted in an increase in the
dielectric constant. Mixes containing limestone aggregate
had a greater dielectric constant than those containing
granite. The dielectric constant decreased with curing
period due to the reduction in free water availability.
Mixes containing higher water/cement ratios exhibited a
higher dielectric constant, especially in the initial
curing period. The admixtures did not significantly
affect the dielectric constant after one day of curing.
After 28 days of curing, however, all three admixtures
had an effect on the measured dielectric constant as
compared to control mixes. Chloride content had a
significant effect on the loss part of the dielectric
constant especially during early curing. A relationship
was also established between the chloride permeability
(based on conductance measurements) of PCC and its
dielectric constant after 75 days of moist curing.<br>Master of Science
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Bittle, James R. "2017 Full Solar Eclipse| Observations and LWPC Modeling of Very Low Frequency Electromagnetic Wave Propagation." Thesis, University of Colorado at Denver, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10843376.
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<p> On August 21, 2017 a total solar eclipse occurred over the United States commencing on the west coast moving across to the east coast providing an opportunity to observe how the rapid day-night-day transition changed the ionosphere’s D-region electron density and how very low frequency (VLF) electromagnetic wave propagation was affected. To observe the solar obscurity effects, VLF receivers were deployed in two locations: one in the path of totality in Lakeside, Nebraska and another south of the totality path in Hugo, Colorado. The locations were chosen to achieve an orthogonal geometry between the eclipse path and propagation path of U. S. Navy VLF transmitter in North Dakota, which operates at 25.2 kHz and has call sign NML. VLF amplitude and phase changes were observed in both Lakeside and Hugo during the eclipse. A negative phase change was observed at both receivers as solar obscuration progressively increased. The observed phase changes became positive as solar obscuration reduced. The opposite trend was observed for the amplitude of the transmitted signal: growth as max totality approached and decay during the shadow’s recession. The Long Wave Propagation Capability (LWPC) code developed by the US Navy was used to model the observations. LWPC is a modal solution finder for Earth-ionosphere waveguide propagation that takes into account the D-region density profile. In contrast to past efforts where a single ionosphere profile was assumed over the entire propagation path, a degree of spatial resolution along the path was sought here by solving for multiple segments of length 100-200 km along the path. LWPC modeling suggests that the effective reflection height changed from 71 km in the absence of the eclipse, to 78 km at the center of the path of totality during the total solar eclipse and is on agreement with past work.</p><p>
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MAROUAN, YOUSSEF. "Etat de polarisation et caracteristiques de propagation moyennes d'emissions em naturelles dans un magnetoplasma froid : application aux donnees ebf du satellite aureol-3." Orléans, 1988. http://www.theses.fr/1988ORLE2040.
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Observation supposee effectuee en un point fixe de l'espace. Cette observation consiste en la mesure simultanee d'au moins trois composantes du champ electromagnetique. Discussion des estimateurs du degre de polarisation proposes par samson. Simulation numerique. Identification experimentale des modes d'une onde multiple en propagation dans ce magnetoplasma (ou deux modes peuvent coexister), obtenue a partir des caracteristiques de polarisation des ondes. Application aux emissions tres basse frequence observees par satellite aureol-3
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Suedan, Gibreel A. "High frequency beam diffraction by apertures and reflectors." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27545.
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Most solutions for electromagnetic wave diffraction by obstacles and apertures assume plane wave incidence or omnidirectional local sources. Solutions to diffraction problems for local directive sources are needed. The complex source point representation of directive beams together with uniform solutions to high frequency diffraction problems is a powerful combination for this. Here the method is applied to beam diffraction by planar structures with edges, such as the half-plane, slit, strip, wedge and circular aperture.
Previously used restrictions to very narrow beams and paraxial regions, are removed here and the range of validity increased. Also it is shown that the complex source point method can give a better approximation to broad antenna beams than the Gaussian function.
The solution derived for the half-plane problem is uniform, accurate and valid for all beam orientations. This solution can be used as a reference solution for other uniform or asymptotic solutions and is used to solve for the wide slit and complementary strip problems.
Uniform solutions for omidirectional sources are developed and extended analytically to become solutions for directive beams. The uniform theory of diffraction is used to obtain uniform solutions where there are no simple exact solutions, such as for the wedge and circular aperture. Otherwise rigorously correct solutions at high frequencies for singly diffracted far fields are used, such as for the half-plane, slit and strip. The geometrical theory of diffraction and equivalent line currents are used to include interaction between edges. Extensive numerical results including the limiting cases; e.g. plane wave incidence, line and point sources are given. These solutions are compared with previous solutions, wherever possible and good agreement is evident
Beam diffraction by a wedge with its edge on the beam axis is analysed. This solution completes a previous asymptotic solution which is infinite on the shadow boundaries and inaccurate in the transition regions. Finally, the diffraction by a circular aperture illuminated by normally incident acoustic beam, is derived and the singularity along the axial caustic is removed using Bessel functions and a closed form expression for multiple diffraction is derived.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
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Kipp, Robert. "Mixed potential integral equation solutions for layered media structures : high frequency interconnects and frequency selective surfaces /." Thesis, Connect to this title online; UW restricted, 1993. http://hdl.handle.net/1773/5974.
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Lachin, Anoosh. "Low frequency waves in the solar system." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267713.
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Clausen, Lasse Boy Novock. "Ultra-low frequency waves in the magnetosphere." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/7533.
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Ultra-low frequency waves, i.e. pulsations between 0.1 and 1,000 mHz, are an inherent feature of space plasmas. These plasmas are largely collisionless and hence waves play an important role as an agent to transfer energy, mass and momentum. This work explores some of the wave's features in the Earth's magnetosphere using several different measurement techniques located in different regions. The first of the three case studies presented describes results from an experiment involving an ionospheric heating facility located on Svalbard. The SPace Exploration by Active Radar (SPEAR) facility periodically changed the ionospheric conductivities, superimposing a AC component on a background DC current. Thus the heated patch acted as a giant virtual antenna, emitting Alfvén waves which were detected by ground-based magnetometers in the vicinity of the heater. The following two case studies investigate naturally occurring waves, using both space- and ground-based instruments. In both cases waves generated at the bow shock penetrated into the magnetospheric cavity where they interacted with the local plasma and magnetic field. Whereas in the first case the propagation path of one individual wave packet is analysed, the last data chapter discusses the generation of Alfvénic continuum by upstream generated waves.
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Borderick, James David. "Ionospheric signatures of ultra low frequency waves." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/9170.
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Ultra Low Frequency (ULF) waves have been studied for many years and the observation and modelling of such phenomena reveals important information about the solar-terrestrial interaction. Being ubiquitous in the collisionless terrestrial space plasma environment, ULF waves represent important physical processes in the transfer of energy and momentum. This thesis comprises three distinct studies to observe, model and analyse ULF phenomena. The first two studies focus on ULF wave observations at high-latitudes in the terrestrial ionosphere using a collection of both space- and ground-based instruments. The first study provides a detailed analysis of the time evolution of a ULF wave using the characteristics of the observed ULF wave as input-parameters to a 1-D numerical model. As the wave signature evolves towards a Field Line Resonance (FLR) a change in the incident wave mode from a partially Alfvénic wave to a purely shear Alfvénic wave is observed. The second study presents statistics of 25 large spatial-scale ULF waves with observations from a high-latitude Doppler sounder and ground-based magnetometers, complemented by model results. The third and final study describes the implementation of a well established radar technique ("double-pulse"), which is new for the Super Dual Auroral Radar Network (SuperDARN), which aims to provide an unprecedented temporal resolution for ULF wave studies. The new pulse sequence increases the temporal resolution of SuperDARN by a factor of three. Preliminary findings suggest this technique yields impressive results for ionospheric scatter with steady phase values but that the method cannot be used for data when the phase is rapidly changing or if the data originates from slowly decorrelating plasma irregularities. The running of two independent pulse sequences on the stereo channels of the Hankasalmi radar has also enabled, for the first time, the observation of cross-contamination between the radar channels.
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Fozard, John Andrew. "Diffraction and scattering of high frequency waves." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433239.
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This thesis examines certain aspects of diffraction and scattering of high frequency waves, utilising and extending upon the Geometrical Theory of Diffraction (GTD). The first problem considered is that of scattering of electromagnetic plane waves by a perfectly conducting thin body, of aspect ratio O(k^1/2), where k is the dimensionless wavenumber. The edges of such a body have a radius of curvature which is comparable to the wavelength of the incident field, which lies inbetween the sharp and blunt cases traditionally treated by the GTD. The local problem of scattering by such an edge is that of a parabolic cylinder with the appropriate radius of curvature at the edge. The far field of the integral solution to this problem is examined using the method of steepest descents, extending the recent work of Tew [44]; in particular the behaviour of the field in the vicinity of the shadow boundaries is determined. These are fatter than those in the sharp or blunt cases, with a novel transition function. The second problem considered is that of scattering by thin shells of dielectric material. Under the assumption that the refractive index of the dielectric is large, approximate transition conditions for a layer of half a wavelength in thickness are formulated which account for the effects of curvature of the layer. Using these transition conditions the directivity of the fields scattered by a tightly curved tip region is determined, provided certain conditions are met by the tip curvature. In addition, creeping ray and whispering gallery modes outside such a curved layer are examined in the context of the GTD, and their initiation at a point of tangential incidence upon the layer is studied. The final problem considered concerns the scattering matrix of a closed convex body. A straightforward and explicit discussion of scattering theory is presented. Then the approximations of the GTD are used to find the first two terms in the asymptotic behaviour of the scattering phase, and the connection between the external scattering problem and the internal eigenvalue problem is discussed.
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Li, Min. "Robust topological design of low frequency electromagnetic devices." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121229.
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This thesis presents an automated topological design system for low frequency electromagnetic devices, e.g. an interior permanent magnet motor. The automated design is carried out through a topological shape optimization process: first, the system employs a topological sensitivity analysis to examine the design domain and to determine the optimal topology (distribution of source and materials); second, the system uses a shape optimizer to further improve the design; these two steps are performed alternately until the optimality condition is satisfied. The robustness of a topology with respect to small variations on its geometries is studied and a robustness measure is defined, originally in the thesis, as the worst case performance of an objective function for the topology and shape optimization. Therefore, the idea of robust design can be applied to the conceptual design (topological design) of electrical machines. Other than the application to motor design, the topology optimization algorithm developed in the thesis, was used originally in the non-destructive testing for quickly location and accurately shape reconstruction of cracks.<br>Cette thèse présente un système automatique de conception topologique pour les dispositifs électromagnétiques à basse fréquence, par exemple, un moteur à aimant permanent intérieur. La conception automatisée est effectuée par un processus d'optimisation topologique de la forme : d'abord, le système emploie une analyse de sensibilité topologique pour examiner le domaine de la conception et déterminer la topologie optimale (répartition des sources et des matériaux); Deuxièmement, le système utilise une optimisation de forme pour améliorer la conception, les deux étapes étant effectuées alternativement jusqu'à ce que la condition d'optimalité est satisfaite. La robustesse de la topologie par rapport à de petites variations est étudiée et une mesure de robustesse est défini, à l'origine dans cette thèse, comme la performance de la fonction objectif, dans le pire des cas, pour l'optimisation topologique de la forme. Le concept de conception robuste peut donc être appliquée à la conception (conception topologique) des machines électriques. Autre que l'application de la conception du moteur, l'algorithme d'optimisation topologique, développé dans la thèse, a été utilisé à l'origine dans le contrôle non destructif pour trouver rapidement les fissures et preciser la forme optimale.
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Miseikis, Vaidotas. "The interaction of graphene with high-frequency acoustic and electromagnetic waves." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595843.
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Devices were developed to explore the perturbation of graphene using high-frequency signals. Two kinds of effects were studied: the interaction of graphene with surface acoustic waves (SAWs) and the propagation of picosecond pulses. The coupling of graphene with SAWs was first studied using flip-chip devices, which employed an evanescent field extending across the gap between the chips. A later design directly integrated layers of graphene grown by chemical vapour deposition (CVD) on piezoelectric 5ubstrates, containing interdigital transducers (IDTs) for SAW generation and detection. Graphene devices were characterised using Raman spectroscopy and atomic force microscopy; the electronic properties of CVD-graphene were investigated by performing magnetoresistance measurements. The measurements of the acoustically-generated current in the direct-coupling devices closely followed the SAW response of the IDTs, demonstrating the acousto-electric effect in graphene for the first time . . In a second class of devices, graphene was transferred to a quartz substrate, and, using on-chip waveguides, integrated with photoconductive switches capable of generating and detecting sub-picosecond pulses, which allow studying THz-frequency transmission in the system. Pulses containing frequency components of up to 2.5 THz were generated in these devices. The demonstration of the acousto-electric effect in graphene paves the way for SAW-based charge manipulation in graphene, such as singleelectron transport. The propagation of picosecond pulses in graphene could be used to further investigate the properties of graphene in the terahertz-frequency range.
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Wilson, Robert John. "Ultra low frequency waves in the Jovian magnetosphere." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251582.
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Apo, Daniel Jolomi. "Low Frequency Microscale Energy Harvesting." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/49773.
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The rapid advancement in complimentary metal-oxide-semiconductor (CMOS) electronics has led to a reduction in the sizes of wireless sensor networks (WSN) and a subsequent decrease in their power requirements. To meet these power requirements for long time of operation, energy harvesters have been developed at the micro scale which can convert vibration energy into electrical energy. Recent studies have shown that for mechanical-to-electrical conversion at the mm-scale (or micro scale), piezoelectric mechanism provides the best output power density at low frequencies as compared to the other possible mechanisms for vibration energy harvesting (VEH). However, piezoelectric-based VEH presents a fundamental challenge at the micro scale since the resonance frequency of the structure increases as the dimension decreases. Electromagnetic induction is another voltage generation mechanism that has been utilized for VEH. However, the electromagnetic induction based VEH is limited by the magnet and coil size and the decrease in power density at the micro scale. Hybrid energy harvesting is a novel concept that allows for increased power response and increased optimization of the generated voltage. The work in this field is currently limited due to integration challenges at small dimensions.
An effective design for low frequency piezoelectric VEH is presented in this work. A unique cantilever design called arc-based cantilever (ABC) is presented which exhibits low natural frequencies as compared to traditional cantilevers. A general out-of-plane vibration model for ABCs was developed that incorporated the effects of bending, torsion, transverse shear deformation and rotary inertia. Different configurations of micro ABCs were investigated through analytical modeling and validation experiments. ABC structures were fabricated for dual-phase energy harvesting from vibrations and magnetic fields.
Next, a levitation-induced electromagnetic VEH concept based on double-repulsion configuration in the moving magnet composite was studied. Computational modeling clearly illustrated the advantages of the double-repulsion configuration over the single-repulsion and no-repulsion configurations. Based on the modeling results, an AA battery-sized harvester with the double-repulsion configuration was fabricated, experimentally characterized and demonstrated to charge a cell phone. The scaling analysis of electromagnetic energy harvesters was conducted to understand the performance across different length scales. A micro electromagnetic harvester was developed that exhibited softening nonlinear spring behavior, thus leading to the finding of nonlinear inflection in magnetically-levitated electromagnetic harvesters. The nonlinear inflection theory was developed to show its causal parameters.
Lastly, a coupled harvester is presented that combines the piezoelectric and electromagnetic voltage mechanisms. The advantages of each mechanism were shown to positively contribute to the performance of hybrid harvester. The cantilever provided low stiffness, low frequency, and pure bending, while the magnetic system provided nonlinearity, broadband response, and increased strain (and thus voltage).<br>Ph. D.
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Davies, Jacob Owen. "Inspection of pipes using low frequency focused guided waves." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503091.
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The aim of the work presented here is to develop a pipe inspection tool that is capable of detecting, locating and then sizing any defects that may be present in the pipe section under test. The work is primarily directed towards quantifying any improvements that can be made to the current screening system by using synthetically focused imaging algorithms. The algorithms are first tested for plate imaging using a linear array and then modified for use on cylindrical structures. The minimal modifications make use of similarities between the guided wave structure in plates and pipes. The pipe imaging system is then rigorously tested using data from 3D finite element model predictions and laboratory experiments. The performance of the system is established at various inspection frequencies in terms of detection sensitivity to circumferential cracks, resolution and robustness towards set up errors. It is found that the defect sensitivity is increased by around 15 dB over the simple screening tool and cracks of circumferential extent larger than ~1.5? can be directly sized from the pipe image.
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Barnes, Timothy. "The generation of low-frequency water waves on beaches." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319128.
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Sen, Mumtaz Bilgin. "Channel estimation techniques for single and multiple transmit antenna orthogonal frequency division multiplexing (OFDM) systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FSen.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2005.<br>Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 71-72). Also available online.
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Masumdar, Salim. "Vibration-based electromagnetic energy harvester for low-frequency road traffic." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10638807.
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<p> In recent times, wireless sensor network (WSN) has played an important role for applications in the biomedical, commercial, and military fields. One of the applications is in intelligent transportation system (ITS), which uses sensors placed under the roads to detect vehicles. Progress in the field of Micro-Electro-Mechanical System (MEMS) has made it possible to make sensors that are small and easy to install, but operate on batteries which need to be replaced on a regular basis. For this reason, an alternative supply of power is necessary to run the sensors more effectively. </p><p> This thesis project proposes an idea in which the road vibrations can be used to harvest energy, which will further be used to supply power to the sensors. The concept of electromagnetic induction is applied to convert traffic-induced road vibrations into electrical energy. This project is more focused on getting maximum output from low vibrations by making use of a repulsive stack arrangement of magnets rather than using a single magnet while keeping the size of the energy harvester small. The simulation model of the harvester was designed using Simulink and COMSOL software. </p><p> The simulation model takes into consideration the vibration data and gives the output voltage generated by the harvester model. Output voltages for road vibrations occurring at different frequencies were tested. Using a repulsive stack approach provided an increase in output voltage compared to a single magnet approach.</p><p>
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Shepherd, Sebastian James. "The effects of extremely low frequency electromagnetic fields on insects." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/422277/.
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Flying insect species are currently in decline, including many species that provide important pollination ecosystem services. Combined exposure to various environmental stressors are associated with insect declines, including land-use change, pesticide use and climate change, but the potential biological and environmental effects of extremely low frequency electromagnetic fields (ELF EMFs) are poorly understood. ELF EMFs are pervasive in the environment, and anthropogenic ELF EMF pollution has increased greatly in recent years. Despite this, little has been done to consider the potential environmental impacts of ELF EMFs. Given that there is evidence that ELF EMFs can have biological effects, it is important to explore these biological stimuli and their potential to affect insects in the environment. Here the biological effects of ELF EMFs on important insect species were investigated, with two-fold aims of both increasing understanding of the biological effects of ELF EMFs, and determining whether field-realisitc levels of ELF EMFs have the potential to cause envrionemental stress to insects. ELF EMF impacts were investigated with the desert locust, as an economically important agricultural pest and a species that provides utility in understanding insect neurophysiology, and the honey bee, as a globally important pollinator and a well known study species for insect cognitive behaviour. Short-term exposure to high levels of ELF EMFs was found to affect neurophysiology, and reduce locomotory function in locusts, as well as increase stress protein levels in bees and locusts, and affect honey bee cognitive behaviour. Acute exposure to ELF EMFs at levels that can be encountered regularly in the environment around man-man sources for ELF EMFs reduced honey bee performance in olfactory learning assays, affected flight behaviour, and affected feeding and flight performance in a semi-field scenario. Further to this, some of these impacts of ELF EMFs on cognitive behaviour and flight were reduced when ELF EMFs were applied in combination with other well-known environmental stressors, neonicotinoid insecticides. These findings give a more detailed indication of some of the physiological effects that may underpin changes in insect locomotory behaviour that occur after short-term exposure. This is the first time that powerline simulating ELF EMFs have been directly measured and applied to insects in the context of considering the ecological effects (and thus using field-realistic exposure levels) of the ELF EMFs, rather than just the biological effects. This is the first indication that short-term and acute ELF EMF exposure can affect insect cognitive behaviour, and these effects have been shown to occur at levels which can be encountered in the field by a globally important pollinator species, the honey bee. This is also the first indication that acute field-realistic ELF EMF exposure can affect insect locomotory behaviour in the environement. This research describes new effects of ELF EMFs on insect biology and establishes that ELF EMFs have a potential to affect insect ecology, such that future ELF EMF understanding must be focused in further exploring mechanisms by with ELF EMFs cause biological effects, as well as the larger scale ecological risk assessment of ELF EMF impacts from powerlines.
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Ma, Zuhui, and 馬祖輝. "Fast methods for low-frequency and static EM problems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/195987.
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Electromagnetic effects play an important role in many engineering problems. The fast and accurate numerical methods for electromagnetic analysis are highly desired in both the low-frequency analysis and the static analysis.
In the first part of this thesis, a low-frequency stable domain decomposition method, the augmented equivalence principle algorithm (A-EPA) with augmented electric field integral equation (A-EFIE), is introduced for analyzing the electromagnetic problems at low frequencies. The A-EFIE is first employed as a inner current solver for the EPA algorithm so that it improves the low-frequency inaccuracy issue. This method, however, cannot completely remove the low-frequency breakdown. To overcome it, the A-EPA with A-EFIE is studied and developed so that it has the capability to solve low-frequency problems accurately.
In the second part, novel Helmholtz decomposition based fast Poisson solvers for both 2-D and 3-D problems are introduced. These new methods are implemented through the quasi-Helmholtz decomposition technique, i.e. the loop-tree decomposition. In 2-D cases, the proposed method can achieve O(N) complexity in terms of both computational cost and memory consumption for moderate accuracy requirements. Although computational costs become higher when more accurate results are needed, a multilevel method by using the hierarchical loop basis functions can obtain the desired efficiency. The same idea can be extend to 3-D case for exploiting a new generation of fast method for electrostatic problems.<br>published_or_final_version<br>Electrical and Electronic Engineering<br>Doctoral<br>Doctor of Philosophy
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Trott, Keith Dennis. "A high frequency analysis of electromagnetic plane wave scattering by a fully illuminated perfectly conducting semi-infinite cone /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487323583622574.
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McChesney, Jon Mearns Bellan Paul Murray Bellan Paul Murray. "Observations of stochastic ion heating by low frequency drift waves /." Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-02092007-143250.
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Elsden, Tom. "Numerical modelling of ultra low frequency waves in Earth's magnetosphere." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/15663.
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Ultra Low Frequency (ULF) waves are a ubiquitous feature of Earth's outer atmosphere, known as the magnetosphere, having been observed on the ground for almost two centuries, and in space over the last 50 years. These waves represent small oscillations in Earth's magnetic field, most often as a response to the external influence of the solar wind. They are important for the transfer of energy throughout the magnetosphere and for coupling different regions together. In this thesis, various features of these oscillations are considered. A detailed background on the history and previous study of ULF waves relevant to our work is given in the introductory chapter. In the following chapters, we predominantly use numerical methods to model ULF waves, which are carefully developed and thoroughly tested. We consider the application of these methods to reports on ground and spaced based observations, which allows a more in depth study of the data. In one case, the simulation results provide evidence for an alternative explanation of the data to the original report, which displays the power of theoretical modelling. An analytical model is also constructed, which is tested on simulation data, to identify the incidence and reflection of a class of ULF wave in the flank magnetosphere. This technique is developed with the aim of future applications to satellite data. Further to this, we develop models both in Cartesian and dipole geometries to investigate some of the theoretical aspects of the coupling between various waves modes. New light is shed on the coupling of compressional (fast) and transverse (Alfvén) magnetohydrodynamic (MHD) wave modes in a 3D dipole geometry. Overall, this thesis aims to develop useful numerical models, which can be used to aid in the interpretation of ULF wave observations, as well as probing new aspects of the existing wave theory.
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Smit, Jacobus Petrus. "Theoretical development and implementation of algorithms for the inversion of frequency domain airborne electromagnetic data into a layered earth." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-02222007-142602.
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Toida, Mieko, Takashi Yoshiya, and Yukiharu Ohsawa. "Low-frequency electromagnetic fluctuations in thermal-equilibrium, multi-ion-species plasmas." American Institute of Physics, 2005. http://hdl.handle.net/2237/7057.
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Demanuele, Charmaine. "Analysis of very low frequency oscillations in electromagnetic brain signal recordings." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/159351/.
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Spontaneous very low frequency oscillations (<0.5 Hz), previously regarded as physiological noise, have of late been increasingly analysed in neuroimaging studies. These slow oscillations, which occur within widely distributed neuroanatomical systems and are unrelated to cardiac and respiratory events, are thought to arise from variations in metabolic demands in the resting brain. However, they also persist during active goal-directed processing, where they predict inter-trial variability in evoked responses and may present a potential source of attention deficit during task performance. This work presents a series of new approaches for investigating: (i) the slow waves in electromagnetic (EM) brain signal recordings, (ii) their contribution in brain function, and (iii) the changes that the slow wave mechanisms undergo during cognitive processing versus resting states. State-of-the-art blind source separation methodologies, including single-channel and spacetime independent component analysis (SC-ICA and ST-ICA), are employed for denoising and dimensionality reduction of multi-channel EM data, and to extract neurophysiologically meaningful brain sources from the recordings. Particularly, magnetoencephalographic (MEG) data of attention-deficit/hyperactivity disorder (ADHD) and control children, and electroencephalographic (EEG) data recorded from healthy adult controls, are analysed. The key analytical challenges and techniques available for the analysis of the slow waves in EM brain signal recordings are discussed, and specific solutions proposed. Core results demonstrate that the inter-trial variability in the amplitude and latency of the eventrelated fields sensory component, the M100 (in MEG), exhibits a slow wave pattern, which is indicative of the intrinsic slow waves modulating underlying brain processes. In a separate study, phase synchronisation in the slow wave band was observed between fronto-central, central and parietal brain regions, and the level of synchrony varied between rest and task conditions, and as a function of ADHD. Furthermore, a new EEG experimental framework and a multistage signal processing methodology have been designed and implemented in order to investigate brain activity during task performance in contrast with that during rest. Here, the brain has been envisaged as an oscillatory system onto which a graded load was imposed to yield a variable output response – the P300. Specifically, results show that the amplitude and phase of the brain sources in the slow wave band share essential similarities during rest and task conditions, but are distinct enough to be classified separately. This is in keeping with the view that the intrinsic slow waves are continuously influencing active brain sources and they are in turn affected by external stimulation. These slow wave variations are also significantly correlated with the level of cognitive attention assessed by performance measures (such as reaction time and error rates). Moreover, the power of the sources in the slow wave band is attenuated during task, and the level of attenuation drops as the task difficulty level is increased, whilst their phase undergoes a change in structure (measured through entropy). These new methodologies, developed for gaining insight into the neurophysiological role of the slow waves, could be used for assessing changes in the brain electrical oscillators as a function of various psychiatric and/or neurobehavioural disorders such as ADHD. This could ultimately lead towards a more scientific (and accurate) approach for the prognosis and diagnosis of these disorders.
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Koyama, Shin. "Genotoxic effects of extremely low frequency electromagnetic fields and radiofrequency radiation." Kyoto University, 2007. http://hdl.handle.net/2433/136436.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(人間・環境学)<br>甲第13165号<br>人博第372号<br>新制||人||91(附属図書館)<br>18||D||173(吉田南総合図書館)<br>UT51-2007-H438<br>京都大学大学院人間・環境学研究科相関環境学<br>(主査)教授 小松 賢志, 助教授 倉橋 和義, 助教授 三浦 智行<br>学位規則第4条第1項該当
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Callegary, James Briggs. "Spatial sensitivity of low-induction-number frequency-domain electromagnetic-induction instruments." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/282901.
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Numerical simulations were used to study spatial averaging in low-induction-number frequency-domain electromagnetic induction (LIN FEM) instruments. Local ( LS) and cumulative (CS) sensitivity were used to analyze three different aspects of LIN FEM spatial sensitivity. LS is the variation in a measured property given a small change at a given location of the property of interest. CS contours are derived from LS and reveal the shape and the fraction of total instrument sensitivity enclosed within the contours. The first study re-evaluated the asymptotic approach to LIN FEM spatial sensitivity. Using this approach, LIN FEM measurements have often been assumed to represent electrical conductivity (sigma) at discreet depths that do not vary with the sigma of the ground. This assumption was tested using simulations of electromagnetic fields in environments with homogeneous and layered sigma distributions. When the induction number was greater than 0.01, the 1-D vertical CS distribution and the depth of investigation varied up to 20% over the range of sigma simulated. As sigma increased, CS contours and depth of investigation decreased in depth. In the second study a small perturbation approach was used to calculate CS distributions so that each distribution is unique to a given LS distribution. CS was summed from regions of high to low LS, and retained information on the magnitude and location of LS. As sigma increased, CS became focused around the highest LS values. The maximum reduction in depth of investigation was about 40% at the highest sigma investigated. In the final study, a series of small, electrically conductive perturbations was simulated in a three-dimensional, homogeneous environment. Three-dimensional LS varied markedly with a large difference between horizontal (HMD) and vertical (VMD) orientations of the transmitter and receiver dipoles. In some regions, the calculated magnetic field intensity with the perturbation was less than that calculated for the host without the perturbation. This occurred for both VMD and HMD orientations of the transmitter. CS contours were highly complex. One dimensional, vertical LS curves extracted from the three-dimensional data were very different from curves from infinite layer simulations.
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Mason, Sammuel P. "Atmospheric effects on radio frequency (RF) wave propagation in a humid, near-surface environment." Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Mar/10Mar%5FMason.pdf.
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Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2010.<br>Thesis Advisor(s): Guest, Peter S. ; Goroch, Andreas K. "March 2010." Author(s) subject terms: Electromagnetic propagation, electromagnetic scattering, groundwave propagation, mathematical techniques, variance reduction. Includes bibliographical references (p. 67-68). Also available in print.
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Kochergov, Roman. "Wave equations for low frequency waves in hot magnetically confined plasmas." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=967545463.
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Dong, Chuanfei. "Heating of ions by low-frequency Alfven waves in solar atmosphere." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37160.
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The exact mechanisms responsible for heating the solar atmosphere in regions such as the chromosphere (partially ionized) and the corona (fully ionized) remain quantitatively unknown. This thesis demonstrates that the ions can be heated by Alfven waves with low frequencies in fully and partially ionized low beta plasmas, which is contrary to the customary expectation. For the partially ionized case, we find the heating process to be less efficient than the scenario with no ion-neutral collisions, and that the heating efficiency depends on the ratio of ion-neutral collision frequency to the ion gyrofrequency. For Alfven waves propagating obliquely to the background magnetic field in fully ionized plasmas, we find the heating process to be more efficient than the situation with Alfven waves propagating along the background magnetic field. Furthermore, the simulation results show the parallel kinetic temperature can become even larger than the perpendicular component for the case of obliquely propagating Alfven waves.
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Narita, Yasuhito. "Low frequency waves upstream and downstream of the terrestrial bow shock." Katlenburg-Lindau Copernicus GmbH, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?idn=979493870.
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Lu, Paul ChihPeng. "Passive cancellation of low frequency sound waves using optimized embedded mechanisms." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1876285421&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Kim, Hyo Tae. "High frequency analysis of EM scattering from a circular conducting cylinder with dielectric/ferrite coating /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487322984315885.
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Kim, Tony C. "Interaction of Very Low Frequency (VLF) and Extremely Low Frequency (ELF) Waves in the Ionospheric Plasma and Parametric Antenna Concept." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1486674973747427.
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TOIDA, MIEKO, and YUKIHARU OHSAWA. "Multi-ion-species effects on low-frequency electromagnetic fluctuations and energy transport." Cambridge University Press, 2006. http://hdl.handle.net/2237/10300.
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Bhakta, Nitin. "Extremely low frequency electromagnetic properties in marine environments with non-parallel interfaces." Thesis, King's College London (University of London), 2001. https://kclpure.kcl.ac.uk/portal/en/theses/extremely-low-frequency-electromagnetic-properties-in-marine-environments-with-nonparallel-interfaces(b13ce673-453d-4aca-925a-a7adf547cb69).html.
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Hill, Steven. "Measurements of low frequency acoustic backscatter from the sea surface." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/31022.
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The overall objective of this thesis was to predict, model and measure low frequency acoustic backscatter from the sea surface zone (SSZ). In particular, the objectives were fourfold: to relate the acoustic backscatter Doppler spectrum to the directional waveheight spectrum (DWS) through a perturbation analysis; to develop instrumentation suitable for measuring the properties of acoustic backscatter from the SSZ; to design and implement signal processing hardware and software to process raw data from the instrument; and to deploy the instrument and make measurements to test the validity of the predictions of the theoretical development.
A theoretical framework was developed to enable a test of the acoustic analogue of the Coastal Ocean Dynamics Applications Radar (CODAR) technique, using beamforming techniques to simulate the CODAR antennas. Expressions relating the CODAR antenna outputs to the output of an array of omnidirectional acoustic point sensors were developed, and mathematical algorithms and techniques were derived to extract information about the DWS of surface gravity waves from acoustic Doppler backscatter measurements with the array. Models were developed and implemented, showing the expected form of the power spectral density of the acoustic Doppler backscatter seen by single omnidirectional receivers, and the expected form of data products of the beamformed array.
An acoustic instrument — the Upward-Looking Sonar Array System (ULSAS) — was developed for stand-alone, remotely controlled operation in both bottom-situated and deep-water, surface-tethered configurations. This device can collect and store large quantities of acoustic data from a multi-element array, under the control of a distant operator over a radio link. The bottom-situated version was deployed in the coastal waters of British Columbia, and the deep water version was deployed in the recent Surface Wave Processes (SWAPP) experiment.
A preliminary test of the acoustic CODAR technique was made, yielding information consistent with the known wind and wave field. The form of the non-directional part of the extracted DWS followed approximately the expected k⁻⁴ shape for k values above saturation. Beamforming results using frequency-domain data show that the Doppler-shifted acoustic backscatter is directional in nature. These are the first results of this kind to be reported.
The deep-water version of ULSAS was tested for the first time during the SWAPP cruise. In spite
of a problem limiting the power output of the projector, estimates of the surface scattering strength parameter over angles of incidence less than 45° were made, showing some surprising departures from the Chapman-Harris empirical formula for S₅ , and interesting angular structure. Measurements of the ambient noise field were also made under calm conditions and during 14 kt winds.<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate
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Emelyanenko, Artyom. "Measurements and interpretation of lateral electromagnetic waves on the surface of low conductivity media." Thesis, Griffith University, 2020. http://hdl.handle.net/10072/393637.
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Measurements of electromagnetic fields are used for a wide range of applications. Often such measurements provide a non-destructive and non-intrusive way of obtaining information about the internal structure and other properties of the medium. Observations may be conducted across a very broad frequency range. Depending on the application domain, the frequency bands may range from the UHF band in biomedical engineering to the ULF band in geophysics.
This thesis reports on several experiments where the electric and magnetic fields were measured on the surface of different media for the purpose of determining the electric properties of the material (electric conductivity and relative permittivity).
A series of interference nulls were observed while measuring the electric field at UHF frequencies on the surface of a large, uniform sand dune. The source of the field was a transmitter buried in sand. The same pattern was observed after substituting the active transmitter with a passive scatterer exposed to a surface located electromagnetic transmitter. The scatterer then became a source of the electromagnetic field producing the interference pattern identical to the pattern observed in case of the active transmitter. Modelling of the surface electric field was done using known closed-form solutions for a uniform halfspace and by using an FDTD EM solver. Both approaches showed a close match with the measured fields. By varying the resistivity and the electric permittivity in the constructed models, it is demonstrated that the observed pattern (position of the nulls, nulls depth) depend on these electric properties. The inverse problem is posed with the goal of determining the electric properties of the material using the observed field. The inverse problem was solved, and the conductivity and relative permittivity of sand were determined. Two experiments conducted in different conditions showed the following results: conductivity 1×10-6 S/m and relative permittivity of 2.13 in dry conditions and conductivity 3×10-3 S/m and relative permittivity of 2.86 in wet conditions.
Another experiment reports the measurements of the surface electric field on the top surface of a small three-dimensional concrete block at microwave frequencies (1 – 5 GHz). A copper rod was placed in concrete during sample manufacturing to serve as a scatterer. The FDTD solver was used for modelling and determining the inverse problem solution.
At VLF frequencies, several experiments were conducted using surface impedance measurement equipment TranSIM. TranSIM allows registering amplitude of the electric and magnetic field in the time domain in the frequency range between 100 Hz – 50 kHz. The equipment was used to measure the EM fields produced by lightning strikes. Data collection was conducted on a site where the geology is known. The short-time Fourier transform was used to obtain the spectra of the electric and magnetic fields and the surface impedance was determined in the frequency range 0.5-20 kHz. Frequency sections of apparent resistivity were constructed along the measurement profiles and can be interpreted in terms of the geological sections.
These experiments and subsequent data interpretation techniques represent a novel approach of determining electric properties of the material by observing the electromagnetic field on the surface of the media.
Experiments conducted at UHF and microwave (S-band) frequencies utilize the innovative approach of using the field reradiated by a passive scatterer embedded in the material. Potential applications allow using that approach for non-intrusive data collection when a passive conductor is already present or can be put in the material during manufacturing.
Experiments conducted at VLF frequency range utilize the data collection equipment developed at Griffith University by Mogensen and Thiel. Novel data collection and data processing approach of registering solitary short samples of electric and magnetic fields produced by lightning strikes is discussed. It is shown that the EM field observed in that way can be used consistently for creating a reliable geoelectric model of the media.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>School of Eng & Built Env<br>Science, Environment, Engineering and Technology<br>Full Text
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Diamanti, Kalliopi. "Active-sensor health monitoring of composite structures using low-frequency Lamb waves." Thesis, Imperial College London, 2005. http://hdl.handle.net/10044/1/8293.
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Drexler, Josef. "Determining the properties of low-frequency Farley-Buneman waves at high latitudes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ58028.pdf.
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Farell, Cesar E. "A theoretical investigation of the low-frequency sound generated by breaking waves." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0002/MQ40967.pdf.
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Eriksson, Tommy. "Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere." Doctoral thesis, Stockholm, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4404.
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Landgren, Markus. "A Survey of Low-Frequency Plasma Waves in the Magnetosphere of Saturn." Thesis, KTH, Rymd- och plasmafysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121328.
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The Cassini mission to Saturn carries a wide variety of instruments to investigate Saturn and its surroundings. Since Cassini is an orbiter, the spatial coverage of this mission far exceeds the few flybys made by earlier spacecraft. We focus on just one of the instruments, and conduct a preliminary analysis of data from five-channel waveform receiver (WFR) which is a part of the Radio and Plasma Wave Science instrument (RPWS). Two electric and three magnetic field components are measured in the 3 Hz to 2.5 kHz band and recorded in the time domain. Interference from other systems of the spacecraft severely complicates interpretation of the electric field spectrum below about 1 kHz. To mitigate this problem we have applied a Blackman-Harris window with a strong sidelobe attenuation, but parts of our analysis is restricted to frequencies above 1 kHz. Various algorithms have been applied to detect and discard erroneous measurements. By analyzing the data we have produced maps of spatial variations in the measured power. The region inside about 9 Saturn radii was found to be particularly active, especially in the electric field measurements. Phenomena that have been seen in the data include dust impacts, electromagnetic whistler-mode hiss and chorus, and electrostatic electron-cyclotron harmonic (ECH) emissions.
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Meyer, Patrik K. (Patrik Kristof). "The impact of high frequency/low energy seismic waves on unreinforced masonry." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38557.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.<br>Includes bibliographical references (p. [85]-87).<br>Traditionally, the high frequency components of earthquake loading are disregarded as a source of structural damage because of their small energy content and because their frequency is too high to resonate with the natural frequencies of structures. This thesis argues that higher frequency waves travelling through stiff masonry structures can trigger two types of failure mechanisms that have not yet been taken into account. First, the high frequencies can cause small vertical inter-stone vibrations that result in irreversible relative displacements of the stones, which may ultimately lead to collapse. The energy needed to cause this deformation and failure comes largely from gravitational forces. The second failure mechanism is associated with the increase of the outward thrust that results from the partial fluidization and densification of the loose granular inner core of some unreinforced masonry walls. Preliminary results of a series of static and dynamic tests, as well as of numerical models, demonstrate the potentially destructive effects of high frequency/low energy seismic waves on unreinforced masonry structures.<br>by Patrik K. Meyer.<br>S.M.
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Myung, Noh Hoon. "A high frequency analysis of electromagnetic plane wave scattering by perfectly-conducting semi-infinite parallel plate and rectangular waveguides with absorber coated inner walls /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487267546980859.
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Shih, Wan-Chun. "Performance analysis of variable code rate signals transmitted over frequency-nonselective, slowly fading channels in a pulse-interference environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FShih.pdf.
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