Дисертації з теми "High frequency electromagnetic field"
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1
Wang, Chunsheng. "Numerical study of RF magnetic field, specific absorption rate and signal to noise ratio in high field MRI." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36887560.
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Wang, Chunsheng, and 汪春生. "Numerical study of RF magnetic field, specific absorption rate and signal to noise ratio in high field MRI." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36887560.
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3
Xu, Xiaoming. "New approximations in finite element calculation in high frequency." Thesis, London South Bank University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245127.
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Tigga, Celine. "Modelling of Measurement Equipment for High Frequency Electromagnetic Fields." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-18894.
Повний текст джерелаАнотація:
The aim of this thesis was to develop a model of a receiver which could be quickly used to analyze radiated interference levels from data captured at the output of the antenna equipment used to measure radiated energy. Active circuits were mainly used in developing this model for the ease with which the design and simulations could be carried out in OrCAD. The guiding document for the thesis work has been CISPR 16-1-1 (International Special Committee on Radio Interference part 16-1-1) which specifies the characteristics and performance of equipment for the measurement of radiated interference. The testing of this receiver model was carried out as far as possible based on the test setups recommended in CISPR, and all results have been compared with the standards laid down for the model. Using the results, it will be shown that a CISPR EMI receiver can be modeled as a simple EMI receiver consisting of filtering, mixing and detecting circuits built according to specifications.
5
Whitman, Daniel Joseph. "Electromagnetic Fields, Power Losses, and Resistance of High-Frequency Magnetic Devices." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1268951694.
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6
Paknys, Robert. "High frequency surface fields excited by a line source on a dielectric coated cylinder /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487259580263306.
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7
Racic, Marin. "Enhancement of Inertial Electrostatic Confinement (IEC) Fusion Through High Frequency Electromagnetic Fields." Honors in the Major Thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/425.
Повний текст джерелаАнотація:
This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucfBachelors
Engineering and Computer Science
Mechanical Engineering
8
Geng, Deli. "High refresh rate three dimensional positioning system using frequency-multiplexed electromagnetic fields." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420040.
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9
Banova, Todorka [Verfasser], Thomas [Akademischer Betreuer] Weiland, and Ursula van [Akademischer Betreuer] Rienen. "Systematic Data Extraction in High-Frequency Electromagnetic Fields / Todorka Banova. Betreuer: Thomas Weiland ; Ursula van Rienen." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://d-nb.info/1110902441/34.
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10
Tadesse, Yonatan Abebe. "The Electromagnetic Simulation of Birdcage Coils for MRI based on Finite Element Method." Youngstown State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1484137190762487.
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11
Meloling, John H. "A caustic corrected uniform geometrical theory of diffraction for evaluating high-frequency electromagnetic fields near the cusp of the caustic caused by the curvature of an edge /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487853913101801.
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12
Pothecary, N. M. "The interaction of high frequency fields with physical objects and the resultant thermal response." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385685.
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13
Cornock, Leigh. "Electromagnetic coupling in high frequency multilayer structures." Thesis, University of Essex, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558827.
Повний текст джерелаАнотація:
The interaction of the electromagnetic fields generated by electronic products, known as Electromagnetic Compatibility (EMC), is a significant consideration within the development process of all electronic products. As products get smaller, faster and more complex, the compliance with international EMC regulations becomes a growing issue. The design of multilayer printed circuit boards (PCS's) and integrated circuits (IC's) have a key impact on the EMC performance of a product and are at the forefront of this research. The PCS layout can be the cause of a product not meeting the required international EMC standards or even impeding the design from working due to the parasitic interaction of parts within the design. Understanding the interaction of elements within a PCS structure is critical to high speed designs. This research investigates the parasitic interaction of plated through holes, known as vias, within multilayer printed circuit board structures. Vias are an unavoidable element in the design of multilayer structures (either PCS or IC) but there is only limited research on the interaction between closely spaced vias. This research investigates how vias in multilayer structures interact. Explicitly this research presents: Unique frequency domain measurements and full wave models of the coupling between closely spaced via structures. A parametric investigation, using electromagnetic modelling, of the impact of via design and layout on the degree of coupling experienced between vias. Consequently design guides / rules of thumb on the reduction of coupling are generated. The development of a novel, lumped element equivalent circuit to enable: accurate and efficient simulation of the coupling between vias. This work helps progress theoretical understanding as well as the practical reality of laying out printed circuit boards. This adds to previous published work in the development of EMC design for high speed multilayer structures.
14
Wang, Jian. "Study of electromagnetic field uniformity in radio frequency heating applicator." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Summer2007/J_Wang082207.pdf.
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15
Meier, Sven Damian. "High-frequency electromagnetic emissions from mechanical switching devices." Thesis, University of Strathclyde, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436097.
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16
Lawson, James. "High frequency electromagnetic links for wireless power transfer." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/54841.
Повний текст джерелаАнотація:
This thesis investigates inductive links used in wireless power transfer systems. Inductive power transfer can be used as a power delivery method for a variety of portable devices, from medical implants to electric vehicles and is gaining increased interest. The focus is on high quality factor coils and MHz operation, where accurate measurements are difficult to achieve. Fast models of all pertinent aspects of inductive power transfer systems for constant cross section coils are developed. These models are used to optimise a new coil winding pattern that aims to increase efficiency in volume constrained scenarios. Measurement systems are developed to measure coil Q factors in excess of 1,000. The prototype measurement systems are verified against models of that system, as well as finite element simulations of the coil under test. Shielding of inductive power transfer systems is then investigated. A structure typically used at GHz frequencies, the artificial magnetic conductor, is miniaturised as an alternative to conventional ferrite backed ground plane shielding. Finite element simulation shows this structure significantly improves link efficiency. The artificial magnetic conductor prototype does not result in a gain in efficiency expected, however it does display the properties expected of an artificial magnetic conductor, including increased coupling factor. Finally, an unconventional inductive power transfer system is presented where transmitter and receiver are up to 6m away from each other and of radically different size. This system provides mW level power to remote devices in a room, for example thermostats or e-ink displays. Conventional approaches to design do not consider the distortion of the magnetic field caused by metallic objects in the room. It was found that treating the system as a decoupled receiver and transmitter provides a better prediction of received power in real world environments.
17
Miah, Mijan. "The high frequency electromagnetic properties of conducting polymers." Thesis, Kingston University, 2000. http://eprints.kingston.ac.uk/20360/.
Повний текст джерелаАнотація:
Organic semiconductors such as polypyrrole, polyalkylthiophenes and polyanilines are being used as alternatives to current materials for electromagnetic interference (EMI) technology. Their production, processability, lightweight construction and cost compare very favourably with those of materials in more established technologies. The project involves the synthesis and purification of the conducting polymers, and the selective use of dopant additives to alter the local structure of the polymer chain, termed as 'doping' in order to produce desired interactions with electromagnetic radiation. Conducting polymers are effectively a new class of microwave absorbing material, and in order to optimise the use of such materials, correlations have been made between the structural variables (e.g. molecular weight, crystal structure, counter-ion size, side-group functionality), the electrical properties ([sigma][sub]dc, [epsilon]*) and the magnetic properties ([mu]*) Polythiophenes and polypyrroles were synthesised using both chemical and electrochemical methods; however, it was found that the chemical methods were more effective, as more processable, soluble and therefore lower molecular weight materials were produced as opposed to the brittle insoluble high molecular weight materials. This allows the manipulation of subtle properties of the conducting polymer such as [epsilon]', [epsilon]", [mu]' or [mu]" in order to enhance the lossy behaviour. These materials were doped to a wide range of conductivities, ranging from the undoped insulating state usually associated with polymers, through a semiconducting up to a metallic state, with conductivities comparable to that of copper. As the conductivity changed, it was found that the electromagnetic radiation could either be transmitted through the polymer material in the insulating state, or be reflected from the material in the conducting state. The intermediate semiconducting form had a maximum absorption of the electromagnetic radiation. The real and imaginary dielectric and magnetic constants of the conducting polymer were measured at microwave frequencies, using a vector network analyser. These conducting polymers were also arranged in a sandwich structure, together with other components with the aim of providing a lightweight, durable and portable device that may be switched 'on' or 'off' under the potentiostatic control, providing a method of controlling the radiation throughout of the device at optical and microwave frequencies. The rate of switching the reflective and transmissive states more conventionally known as the doped and undoped states respectively was controlled by the ionic volume of the dopant ions. The ionic value of dopant ions was determined to be < 1.8x10[sup]-27m[sup]3 based on using a variety of dopant ion volumes and measuring the diffusion coefficients. This device was constructed using a variety of techniques to determine which arrangement would confer the fastest switching time and give the best 'radiation absorbing characteristics'. A variety of conducting polymers, electrode and electrolyte combinations were used in order to fabricate a lightweight and portable device that could be made to interact with the incident electromagnetic radiation. This project investigates the effect of electromagnetic absorption with paramagnetic metal ion complexation to conducting polymers. Current electromagnetic absorption technology addresses either the electric component or the magnetic component of the electromagnetic wave. It has been established that an oscillating electromagnetic field is absorbed to some extent by conducting polymers by the excitation of the mid-gap states at intermediate doping levels. However, this addresses only the electric component of the electromagnetic wave. By complexing paramagnetic ions within the polymer chain, it is expected that this will provide additional electromagnetic absorption. With the electrochromic properties of conducting polymers being well understood, it is also the aim of this project to use the complexed conducting polymer to switch between the conducting and insulating state under the user's control. It is therefore of interest to find the limiting factors affecting the rate of switching. It was found that the complexation of magnetic ions into the polymer contributed to electromagnetic absorption by providing additional loss mechanisms for the incident radiation. Low conductivity materials that were doped to 3-5 mol% and were governed by DC conduction processes were the best absorbers of the electromagnetic radiation.
18
Ivrissimtzis, Leonidas P. "High frequency electromagnetic scattering by conducting polyhedral structures /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487683049375339.
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19
Gulick, Sidney Luther. "Ion injection into radio frequency quadrupole field devices." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66038.
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20
Harrison, Robert Anthony. "An electromagnetic field model for the design of RF reed relays." Thesis, University of Plymouth, 2000. http://hdl.handle.net/10026.1/2678.
Повний текст джерелаАнотація:
A model of the electromechanical characteristics, electrostatic characteristics and coil eddy current losses of a reed relay was developed. These characteristics were returned from reed and coil dimensions. The model was intended as an aid to the design of reed relays for Radio Frequency (RF) and high voltage applications. An electromechanical model of a reed switch and coil was developed using a combination of an axisymmetric finite element model and analytical methods. The characteristics returned from this model were operate, release and differential amp turns, contact gap and contact force. Inclusion of results for contact resistance against contact force yielded the contact resistance characteristics. Electrostatic force between reed contacts was calculated and a criteria for contact arcing in a vacuum applied to allow prediction of breakdown voltage in an evacuated reed switch. The above elements were incorporated in a "Reed Switch Design Program" in which operating, contact resistance and breakdown voltage characteristics were calculated from reed and coil dimensions. Results were found to be in agreement with measured values for three reed switch types. Eddy current losses in relay coils were investigated through experimental measurement of losses occurring in coils mounted around a copper conductor carrying a high frequency current. The losses occurring in the coil were found to present an effective resistance to the current in the conductor. The influence of coil dimensions and the magnetic properties of the conductor on losses were observed. An analytical model of eddy current losses was derived from first principals results and were found concordant with those measured. An "RF Reed Relay Design Program" embodying the eddy current loss model and preceding work was created to demonstrate how relay performance (and efficiency) can be enhanced by tuning reed and coil dimensions. An example of its successful application to product development at Crydom Magnetics Ltd is presented. Proposals for future work are included.
21
Suedan, Gibreel A. "High frequency beam diffraction by apertures and reflectors." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27545.
Повний текст джерелаАнотація:
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.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
22
Golze, Christian. "Tunable High-Field/ High-Frequency ESR and High-Field Magnetization on Single-Molecule Clusters." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1199739868406-44757.
Повний текст джерелаАнотація:
In this work, low dimensional iron group clusters have been studied by application of high magnetic fields. The magnetization has been probed with an MPMS as function of temperature and field. The combination with pulse field measurements up to 52\,T allowed determination of the magnetic exchange coupling parameters, and to probing the effective spin of the ground state. The main focus was on tunable high-field/high-frequency (tHF) ESR in static fields < 17 T and pulse field ESR up to 36 T. This magnetic resonance method has been used for the characterization of the local magnetic properties: The detailed analysis of the field dependence of dedicated spin states allowed to determine the magnetic anisotropy and g-factors. The results were analyzed in the framework of the appropriate effective spin Hamiltonians in terms of magnetization fits and ESR spectrum simulations.
23
Golze, Christian. "Tunable High-Field/ High-Frequency ESR and High-Field Magnetization on Single-Molecule Clusters." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A24034.
Повний текст джерелаАнотація:
In this work, low dimensional iron group clusters have been studied by application of high magnetic fields. The magnetization has been probed with an MPMS as function of temperature and field. The combination with pulse field measurements up to 52\,T allowed determination of the magnetic exchange coupling parameters, and to probing the effective spin of the ground state. The main focus was on tunable high-field/high-frequency (tHF) ESR in static fields < 17 T and pulse field ESR up to 36 T. This magnetic resonance method has been used for the characterization of the local magnetic properties: The detailed analysis of the field dependence of dedicated spin states allowed to determine the magnetic anisotropy and g-factors. The results were analyzed in the framework of the appropriate effective spin Hamiltonians in terms of magnetization fits and ESR spectrum simulations.
24
Сидорук, Юрій Кіндратович. "Пристрої опромінення діелектричних сипучих матеріалів електричним ВЧ та електромагнітним НВЧ полями". Doctoral thesis, Київ, 2016. https://ela.kpi.ua/handle/123456789/17770.
Повний текст джерелаАнотація:
В дисертаційній роботі розглянуто принципи побудови пристроїв опромінення діелектричних сипучих матеріалів, в тому числі зерна,
електромагнітним полем НВЧ та електричним полем ВЧ, що забезпечують рівномірне опромінення сировини та високу енергетичну ефективність камери, в якій відбувається опромінення (активній камері). Детально
проаналізовано активну камеру ВЧ пристрою.
В НВЧ діапазоні запропоновано три варіанти побудови пристроїв, в яких вказані вище вимоги забезпечуються багаторазовим проходженням електромагнітної хвилі через шар сировини. Для забезпечення рівномірного опромінення в ВЧ діапазоні запропонована багатоелектродна камера, на циліндричній поверхні якої розташовано n електродів, що живляться гармонійною напругою. Проведено детальний аналіз напруженості і потенціалу електричного поля в відкритій комплексній області з кільцевою багатозв’язною
границею з використанням теорії функцій комплексної змінної і теорії сингулярних інтегральних рівнянь. Проведено аналіз електричного поля шляхом представлення його як суми просторових гармонік. Показано, що
даний підхід спрощує аналіз при оцінці зони однорідності поля. Розглянуто принцип побудови багатофазного генератора, що живить
багатоелектродну структуру, принцип побудови багатоканального фазозсувача і запропоновано апарат його розрахунку.
25
Chen, Quan, and 陈全. "Efficient high-frequency electromagnetic simulation in VLSI: rough surface effects and electromagnetic-semiconductor coupled simulation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44904940.
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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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27
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.
Повний текст джерелаАнотація:
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.
28
Williams, Thomas. "Full-wave simulation of high-frequency electromagnetic propagation through inhomogeneous plasma." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/8780/.
Повний текст джерелаАнотація:
The propagation of EM radiation past wavelength-sized inhomogeneities is not well understood, yet is of importance for both microwave heating and diagnostic applications in tokamaks. The work presented in this thesis improves this understanding; for this purpose, EMIT-3D, a new finite-difference time-domain (FDTD) code implementing a cold-plasma model has been written to extend full-wave simulations of propagation in magnetized plasmas to 3D. The numerical development of the algorithm is presented and supported with a new stability analysis. Studies of propagation past density filaments (`blobs') are presented and compared with 2D simulations. The synergistic effects of blob density and width on scattering angle are investigated, resulting in the conclusion that even filaments of densities below beam critical density can cause significant deviation in beam paths over a wide frequency range. Further to this, the case of oblique incidence is an explicitly 3D interaction, and its effects have been calculated. The broadening and defocusing effect on microwave beams caused by realistic edge turbulence, observed in all magnetic fusion devices, is also investigated. A fluid model for edge turbulence is used to produce realistic turbulent profiles, which in turn are used to initialise a set of microwave propagation simulations. The effect of propagation through a turbulent layer is observed even at low fluctuation amplitude, and observed to have a peak when eddy sizes approach beam wavelength. This work supports MAST experiments using the SAMI diagnostic to image microwave emission from the plasma edge due to mode conversion from electron Bernstein waves; however, it has relevance for numerous microwave diagnostic, heating and current drive applications in plasmas.
29
Jones, Alexa. "Radio frequency coils for ultra-high field MRI." Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490979.
Повний текст джерелаАнотація:
The push toward higher magnetic fields in MRI has consistently thrown up new challenges in hardware development. The recent development of a new generation of ultra-high field scanners for human imaging is no exception. The earch presented in this thesis aims to provide solutions to new technical challenges in radio-frequency probe design. All probe designs were developed for use at 7T on a Philips Acheiva full body scanner.
30
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.
Повний текст джерелаАнотація:
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.
31
Coats, J. "High frequency asymptotics of antenna/structure interactions." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249595.
Повний текст джерелаАнотація:
This thesis is motivated by the need to calculate the electromagnetic fields produced by sources radiating in the presence of conductors. We begin by reviewing existing theory concerning sources in the presence of flat structures. Various extensions to the canonical Sommerfeld problem are considered. In particular we investigate the asymptotic solution for a finite source that focusses its energy at a point. In chapter 5 we review and extend the asymptotic results concerning illumination of a convex perfect conductor by an incident plane wave and outline the procedure for decoupling the electromagnetic surface field into two scalar modes. In chapter 6 we place a source on a perfect conductor and obtain a complete asymptotic solution for the fields. Special attention is paid to the asymptotic structure that smoothly matches between the leading order lit and shadow regions. We also investigate the degenerate case where one of the curvatures of the perfect conductor is zero. The case where the source is just off the surface is also investigated. In chapter 8 we use the Euler-Maclaurin summation formula to cheaply calculate the fields due to complicated arrays of point dipoles. The final chapter combines many earlier results to consider more general sources on the surface of a perfect conductor. In particular we must introduce new asymptotic regions for open sources. This then enables us to consider the focussing of the surface field due to a finite source. The nature of the surface and geometrical optics fields depends on the size of the source in comparison to the curvatures of the surface on which they lie. We discuss this in detail and conclude with the practical example of a spiral antenna.
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Otín, R. (Rubén). "Regularized Maxwell equations and nodal finite elements for electromagnetic field computations in frequency domain." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/109966.
Повний текст джерелаАнотація:
En esta tesis se presenta una alternativa a la formulación clásica de elementos finitos basada en elementos de arista (edge elements) y las ecuaciones de Maxwell curl-curl. Este enfoque alternativo se basa en elementos nodales y las ecuaciones de Maxwell regularizadas. Las ventajas son que, sin añadir incógnitas adicionales (tales como los multiplicadores de Lagrange), ofrece soluciones sin modos espurios y matrices bien acondicionadas. Además, su representación integral tiene en un orden de singularidad inferior (orden 1 en vez de 3), lo que la hace más adecuada para la hibridación con técnicas numéricas basadas en métodos integrales. Por otro lado, surgen nuevas dificultades que no estaban presentes en la formulación clásica. El principal inconveniente es que se obtiene una solución globalmente errónea si el campo electromagnético tiene una singularidad en el dominio del problema. Además, las condiciones de contorno y las discontinuidades de los campos al cambiar de medio son más laboriosas de implementar. Este trabajo explica la manera de superar estas dificultades y demuestra que se pueden obtener soluciones precisas con elementos nodales y la formulación regularizada.
También se presenta ERMES, un código en C++ que es la implementación de la formulación de elementos finitos mencionada en el párrafo anterior. Calcularemos con ERMES los parámetros de scattering de filtros de microondas y la tasa de absorción específica inducida en un cuerpo cuando está expuesto a campos electromagnéticos. ERMES es también la herramienta de cálculo utilizado en dos nuevos modelos numéricos presentados por primera vez en esta tesis. El primer modelo sirve para caracterizar procesos de conformado electromagnético y el segundo para obtener la impedancia de transferencia del apantallamiento de cables coaxiales perforados.
El modelo de conformado electromagnético calcula la fuerza de Lorentz impulsora del proceso y estima a su vez la frecuencia óptima a la que puede obtenerse la deformación máxima de la pieza. La principal ventaja del método es que proporciona una relación explícita entre la capacidad del banco de condensadores y la frecuencia de la descarga, que es un parámetro clave en el diseño de un sistema de conformado electromagnético. El uso de la formulación regularizada en esta aplicación pone de manifiesto su excelente comportamiento en problemas de baja frecuencia (cuasi-estáticos).
El segundo modelo presentado en este trabajo calcula la impedancia de transferencia de los apantallamientos perforados de cables coaxiales. Este modelo reproduce el comportamiento en alta frecuencia de la impedancia de transferencia con mayor precisión que los métodos encontrados en la literatura y, además, es capaz de analizar una mayor variedad de geometrías y materiales.In this thesis, we present an alternative approach to the usual finite element formulation based on edge elements and double-curl Maxwell equations. This alternative approach is based on nodal elements and regularized Maxwell equations. The advantages are that, without adding extra unknowns (such as Lagrange multipliers), it provides spurious-free solutions and well-conditioned matrices. Besides, its integral representation involves a less singular kernel (order 1 instead of 3), which makes this approach best suited to hybridization with integral numerical techniques. On the other hand, new difficulties arise that were not present in the classical formulation. The main drawback is that a globally wrong solution is obtained when the electromagnetic field has a singularity in the problem domain. Also, boundary conditions and field discontinuities are more laborious to implement. This work explains how to overcome these difficulties and demonstrates that accurate solutions can be obtained with nodal elements and the regularized formulation. We also present ERMES, the C++ implementation of the finite element approach depicted above and the main deliverable of this work. We compute with ERMES the scattering parameters of microwave filters and the specific absorption rate induced in a body when exposed to electromagnetic fields. ERMES is also the computational tool used in two novel numerical models introduced in this thesis. The first one characterizes electromagnetic metal forming processes and the second one the transfer impedance of cable shields. The electromagnetic metal forming model calculates the driving Lorentz force and estimates the optimum frequency at which it is attained the maximum workpiece deformation. The main advantage of the approach is that it provides an explicit relation between the capacitance of the capacitor bank and the frequency of the discharge, which is a key parameter in the design of an electromagnetic forming system. The use of the regularized formulation in this application reveals its excellent behavior in the low-frequency (quasi-static) regime. The second numerical model introduced in this work computes the transfer impedance of cable shields. The model reproduces the high frequency behavior of the transfer impedance more accurately than the approaches found in the literature and, moreover, it is able to analyze a wider variety of geometries and materials.
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Vazquez, Kalty. "Synthesis of Carbon Nanotubes Using High Voltage and High Frequency Induction Field." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/1031.
Повний текст джерелаАнотація:
The fields of nanomaterial and nanostructures are some of the fastest growing fields in material science today. Carbon nanotubes are at the forefront of these fields and their unique mechanical and electrical properties are of great interest to those working in multiple engineering fields.
The overall objective of this study was to design and develop a new process and the equipment necessary, to synthesize carbon nanotubes using high voltage and a high-frequency induction field. This was the first time that a high voltage and an induction field have been used simultaneously in high yield production of carbon nanotubes.
The source of carbon came from acetylene with cobalt used as the doping agent. The carbon was molded into carbon nanotubes by the high-voltage field. The carbon nanotubes were characterized using electron microscope techniques. Raman spectroscopy was also used to reveal the defects and graphitic structures of the carbon nanotubes.
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Lee, Daniel. "Radio frequency probes for ultra-high field magnetic resonance imaging." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/11889/.
Повний текст джерелаАнотація:
This thesis describes the design, construction and testing of a dome coil. The dome coil is hemispherical in shape and is intended to be used within a set of hemispherical gradient coils in a seven tesla magnetic resonance imaging magnet. The dome coil has eight independent elements and is designed to be used for parallel transmission and reception. It is shown that the dome coil produces less specific absorption rate than a conventional birdcage coil and is suitable for head imaging. A study of travelling wave magnetic resonance imaging is also presented. In this study two different methods of generating a travelling wave (using a patch antenna and an end-fire helix antenna) are compared, and the power requirements and specific absorption rate of the travelling wave approach are considered. It is concluded that travelling wave magnetic resonance imaging is best performed using a local receive coil and with the travelling wave antenna placed at least 50 cm from the subject. All theory relevant to the design, construction, testing and use of these coils and antennas is also presented.
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Fuchs, Martin R. "A high field, high frequency electron paramagnetic resonance spectrometer (360 GHz, 14 T)." [S.l. : s.n.], 1999. http://www.diss.fu-berlin.de/2000/7/index.html.
Повний текст джерела
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Badenhorst, J. "Metrology and modelling of high frequency probes." Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/808.
Повний текст джерела
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Sun, Bingyao. "High-Frequency Oriented Design of Gallium-Nitride (GaN) Based High Power Density Converters." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85054.
Повний текст джерелаАнотація:
The wide-bandgap (WBG) devices, like gallium nitride (GaN) and silicon carbide (SiC) devices have proven to be a driving force of the development of the power conversion technology. Thanks to their distinct advantages over silicon (Si) devices including the faster switching speed and lower switching losses, WBG-based power converter can adopt a higher switching frequency and pursue higher power density and higher efficiency.
As a trade-off of the advantages, there also exist the high-frequency-oriented challenges in the adoption of the GaN HEMT under research, including narrow safe gate operating area, increased switching overshoot, increased electromagnetic interference (EMI) in the gate loop and the power stages, the lack of the modules of packages for high current application, high gate oscillation under parallel operation. The dissertation is developed to addressed the all the challenges above to fully explore the potential of the GaN HEMTs.
Due to the increased EMI emission in the gate loop, a small isolated capacitor in the gate driver power supply is needed to build a high-impedance barrier in the loop to protect the gate driver from interference. A 2 W dual-output gate driver power supply with ultra-low isolation capacitor for 650 V GaN-based half bridge is presented, featuring a PCB-embedded transformer substrate, achieving 85% efficiency, 1.6 pF isolation capacitor with 72 W/in3 power density. The effectiveness of the EMI reduction using the proposed power supply is demonstrated.
The design consideration to build a compact 650 V GaN switching cell is presented then to address the challenges in the PCB layout and the thermal management. With the switching cell, a compact 1 kW 400 Vdc three-phase inverter is built and can operate with 500 kHz switching frequency. With the inverter, the high switching frequency effects on the inverter efficiency, volume, EMI emission and filter design are assessed to demonstrate the tradeoff of the adoption of high switching frequency in the motor drive application. In order to reduce the inverter CM EMI emission above 10 MHz, an active gate driver for 650 V GaN HEMT is proposed to control the dv/dt during turn-on and turn-off independently. With the control strategy, the penalty from the switching loss can be reduced.
To build a high current power converter, paralleling devices is a normal approach. The dissertation comes up with the switching cell design using paralleled two and four 650 V GaN HEMTs with minimized and symmetric gate and power loop. The commutation between the paralleled HEMTs is analyzed, based on which the effects from the passive components on the gate oscillation are quantified. With the switching cell using paralleled GaN HEMTs, a 10 kW LLC resonant converter with the integrated litz-wire transformer is designed, achieving 97.9 % efficiency and 131 W/in3 power density. The design consideration to build the novel litz-wire transformer operated at 400 kHz switching frequency is also presented.
In all, this work focuses on providing effective solutions or guidelines to adopt the 650 V GaN HEMT in the high frequency, high power density, high efficiency power conversion and demonstrates the advance of the GaN HEMTs in the hard-switched and soft-switched power converters.Ph. D.
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Gross, Eugene Joseph 1960. "OPTICAL MAGNETIC FIELD PROBE WITH LIGHT EMITTING DIODE SENSOR (RADIO FREQUENCY, FARADAY'S LAW, INCANDESCENT, TEMPERATURE COMPENSATION, INDUCTRON)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276393.
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Schiantarelli, Harry Thornberry. "Performance analysis of high frequency single-site-location antenna arrays using numerical electromagnetic modeling." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA240868.
Повний текст джерелаАнотація:
Thesis (M.S. in Electrical Engineering and M.S. in Systems Engineering (Electronic Warfare))--Naval Postgraduate School, September 1990.Thesis Advisor(s): Adler, Richard W. Second Reader: Jauregui, Stephen. "September 1990." Description based on title screen as viewed on December 18, 2009. DTIC Descriptor(s): Electronic Support Measures, Direction Finding, Propagation, Warfare, Models, Performance Tests, Paths, Theses, Reflection, Vertical Orientation, Electromagnetic Radiation, Coordinates, Communication And Radio Systems, Radio Waves, Antenna Arrays, Law Enforcement, Ionospheric Propagation, Triangulation, Mathematical Models, Ionosphere. Author(s) subject terms: Single-Sight-Location, Direction Finding, High Frequency, Numerical Electromagnetics Code. Includes bibliographical references (p. 116). Also available in print.
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Fenton, David Richard. "An experimental investigation into the electromagnetic compatibility aspects of high frequency power line communications." Thesis, Open University, 2006. http://oro.open.ac.uk/54632/.
Повний текст джерелаАнотація:
Power line communications technology, long established for low data rate applications, is now charting new territory with respect to data rates and provided services. This can only be achieved by increasing PLC operating frequencies from the low frequency band (below 148.5 kHz) to the high frequency band (1 MHz and upwards). There is now only one technical barrier to widespread deployment - Electromagnetic Compatibility. Existing low voltage power networks are optimised for the safe supply of electrical energy. Low voltage cables are often pseudo co-axial in their cross section, but when high frequency signals are coupled onto the network, part of the signal will be radiated. There is therefore a potential for interference to be caused to legitimate users of the radio spectrum. This thesis, and the experimental program underlying it, seeks to quantify potential problems and to propose mechanisms by which they could be mitigated to the extent that wide scale deployment of PLC networks becomes possible. The first part of the thesis offers a detailed introduction to the topics of electricity supply networks, power line communications, modulation techniques and electromagnetic compatibility. Existing EMC standards are examined and although some do not directly cover power line communications networks, key principals are drawn for later use in standards development. The thesis then seeks to examine the mechanisms by which high frequency interference might be caused. Radio propagation modes are discussed and a clear technical distinction is drawn between localised interference from a single PLC network to an individual radio user, and cumulative interference from wide spread deployment of PLC systems. Both such scenarios are examined in detail. The experimental program IS described quantifying radiated signal strength regression from a number of power networks and at a number of operating frequencies within the high frequency band. In this context, signal strength regression is the rate at which electrical field strength reduces with increasing measurement distance. The experimental setup uses a conventional signal generator to supply single test frequencies of known power spectral density, which are coupled onto a power network. The subsequent radiated signal is received via a conventional antenna and radio receiver at a number of locations surrounding the power network at known distances, and signal regression is derived. The experiment was repeated for a number of different frequencies and at representative urban, suburban and rural locations. Indeed, the experimental technique was evolved over a number of months to allow increased portability of the signal receiving equipment, and hence the number of measurements that could be taken. From the experimental results, presented both In tabular and graphical format, a number of conclusions can be drawn. Firstly, based on these results, antenna factors in the order of 85 dB/m can be expected of power line communication networks. It can be concluded that the field strength regression to be anticipated from PLC networks is likely to be significantly below the -20 dB per decade 'free space' regression figure that has often been used in interference models. In fact a regression figure of -35 dB/decade IS more representative of ground wave propagated interference from PLC networks. It is also possible to conclude that the adoption of orthogonal frequency division multiplexing as a multi-carrier spectral technique offers specific advantages in EMC terms. Due to its nature, it is possible to apply a frequency 'mask' to an OFDM based PLC system. Such a mask might be static, applied on a national or regional basis in order to guarantee non-interference with specific frequencies, for example those used for emergency radio channels. It would also be possible to add a dynamic frequency mask, controllable on each PLC system, to mitigate interference with radio services operating within the PLC operating band.
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Liu, Zidong. "High Frequency Inverter Power Stage Design Considerations for Non-Magnetic Materials Induction Cooking." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/40674.
Повний текст джерелаАнотація:
Recently induction cookers, which are based on induction heating principle, have become quite popular due to their advantages such as high energy efficiency, safety, cleanliness, and compact size. However, it is widely known that with current technology, induction cookers require the cookware to be made of magnetic materials such as iron and stainless steel. This is why a lot of cookware is labeled â Induction Readyâ on the bottom. The limited choice of â Induction Readyâ cookware causes inconvenience to customers and limits the growing popularity of the induction cooker. Therefore, a novel induction cooker, which can work for non-magnetic material cookware such as aluminum and copper, can be very competitive in the market.
This thesis studies the induction cooking application; briefly introduces its fundamental principle, research background and the motivation of the development of a non-magnetic material induction cooker. Followed by the research motivation, three commonly used inverter topologies, series resonant inverter, parallel resonant inverter, and single-ended resonant inverter, are introduced. A comparative study is made among these three topologies, and the comparative study leads to a conclusion that the series resonant inverter is more suitable for non-magnetic material induction cooking application.
The thesis also presents several major issues about non-magnetic material induction cooking and how to deal with these issues through induction coil design, higher operating frequency and novel control strategy. Because of non-magnetic materialâ s low resistivity and permeability characteristics, it is difficult to be heated and to achieve soft-switching while the coupling between the induction coil and the cooking pan can be easily changed. Later in this thesis, these issues will be discussed in detail and some potential solutions to these issues such as self-sustained oscillating control, optimized induction coil design, proper selection of power semiconductor device, etc.
A 1.5 kW high frequency series resonant inverter with self-sustained oscillating control is prototyped. Experimental results demonstrated successful operation of the resonant inverter under up to 1.5 kW, and the inverterâ s capability to maintain zero-voltage turn-on during wide operating condition is confirmed.
At the end, a summary is given about the research work done in the thesis and future research work is discussed.Master of Science
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Wang, Tong. "Enhanced Field Emission Studies on Nioboim Surfaces Relevant to High Field Superconducting Radio-Frequency Devices." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29284.
Повний текст джерелаАнотація:
Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling.
The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE.
To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance.
EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m.
To address concerns on the effect of natural air drying process on EFE, a comparative study was conducted on Nb and the results showed insignificant difference under the experimental conditions.
Nb thin films deposited on Cu present a possible alternative to bulk Nb in superconducting cavities. The EFE performance of a preliminary energetically deposited Nb thin film sample are presented.Ph. D.
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Sun, Zhishen. "Application of Lorentz Force in Ultrasound-electromagnetic-field-coupled Electrical Impedance Tomography and Elastography." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1261.
Повний текст джерелаАнотація:
La première partie de la thèse étudie le balayage des gradients de conductivité électrique avec la force de Lorentz induite par ultrasons (SECG-UILF). Pour réduire la puissance de stimulation instantanée du transducteur émetteur et en même temps la pression acoustique maximale du transducteur, cette thèse propose d'appliquer l'excitation de l'impulsion ultrasonore à la modulation de fréquence linéaire ou l'excitation de l'impulsion ultrasonore à fréquence sinusoïdale dans SECG-UILF. Pour les gradients de conductivité électrique à balayage avec la force de Lorentz induite par l’ultrasons à la modulation de fréquence linéaire (SECG-LFM-UILF), un signal électrique de puissance instantanée maximale de 39,54 dBm est utilisé pour exciter le transducteur de transmission, ce qui est inférieur de 25,5 dB à la puissance instantanée maximale de l'impulsion étroite haute tension négative (65,05 dBm) adopté dans le SECG-UILF traditionnel. Et en temps, la pression acoustique d'émission maximale dans le SECG-LFM-UILF est inférieure de 0,44 MPa à celle du SECG-UILF traditionnel. Des expériences de SECG-LFM-UILF sont effectuées en utilisant des fantômes de conductivité à la gélose saline à plusieurs formes de conductivité allant de 0,2 S/m à 0,5 S/m, ce qui montre que: (1) le SECG-LFM-UILF peut détecter avec précision la distance longitudinale des gradients de conductivité électrique; (2) le rapport signal sur bruit des images de balayage B reconstituées de la distribution de gradient de conductivité électrique par le SECG-LFM-UILF est comparable à celui obtenu par le biais du SECG-UILF traditionnel; et (3) en utilisant une largeur de bande de fréquence de modulation de 2 MHz et une durée de modulation de 500 μs, une résolution longitudinale de 1 mm est obtenue. Pour balayer des gradients de conductivité électrique avec une force de Lorentz induite par ultrasons à fréquence fréquentielle (SECG-SF-UILF), le schéma de démodulation en phase présente une implémentation matérielle plus simple que le schéma de démodulation IQ, mais ne peut détecter que la moitié de la plage longitudinale. Des expériences de SECG-SF-UILF sont effectuées sur un échantillon de feuille de cuivre à deux couches, qui démontrent qu’en utilisant une largeur de bande de fréquences de 2 MHz et 64 fréquences discrètes, la plage longitudinale de l’échantillon peut être détectée avec précision. La deuxième partie de la thèse étudie l'élastographie à base d'approche de corrélation croisée. Pour élargir la largeur de bande de fréquence du champ de déplacement de l’onde de cisaillement afin d’améliorer la qualité de la carte de vitesse de l’onde de cisaillement, cette partie étudie l’application de la force de Lorentz pour la génération de champs d’onde de cisaillement. Tout d'abord, la génération des sources des ondes de cisaillement sur la surface du support souple à travers le mécanisme de la force de Lorentz est étudiée en stimulant un anneau ou un patch conducteur non ferromagnétique avec un champ magnétique transitoire. La mesure de déplacement à l'aide d'une sonde laser interférométrique confirme les caractéristiques d'origine, de fréquence et d'amplitude de la force de Lorentz. Sous un champ magnétique transitoire dont la vitesse de changement est de 10,44 kTs-1, le patch génère une source de champ des ondes de cisaillement d'amplitude de 100 µm à la surface de l'échantillon de fantôme d'alcool polyvinylique (PVA). Ensuite, le potentiel des champs d'ondes de cisaillement générés pour la reconstruction de la vitesse des ondes de cisaillement basée sur la corrélation croisée est exploré. Sur la base de l’approche de corrélation croisée, les cartes qualitatives de la vitesse des ondes de cisaillement sont reconstruites à partir de 100 cadres des champs de déplacement, à partir desquels les interfaces ou les limites entre des régions de rigidité différente peuvent être clairement reconnues, lesquelles sont complètement dissimulées dans les images ultrasonoresThe first part of the thesis studies the scanning electric conductivity gradients with ultrasonically induced Lorentz force (SECG-UILF). To reduce the instantaneous stimulation power to the transmitting transducer and at the same time the peak acoustic pressure from the transducer, this thesis proposes to apply the linearly frequency-modulated ultrasound pulse excitation or the sinusoidal step-frequency ultrasound pulse excitation in SECG-UILF. For the scanning electric conductivity gradients with linearly frequency-modulated ultrasound-induced Lorentz force (SECG-LFM-UILF), electrical signal of peak instantaneous power of 39.54 dBm is used to excite the transmitting transducer, which is 25.5 dB lower than the peak instantaneous power of the negative high-voltage narrow pulse (65.05 dBm) adopted in traditional SECG-UILF; and at the same time, the peak transmitting acoustic pressure in SECG-LFM-UILF is 0.44 MPa lower than that in traditional SECG-UILF. Experiments of SECG-LFM-UILF are done using multi-shaped saline agar phantoms of conductivity ranging from 0.2 S/m to 0.5 S/m, which show that: (1) the SECG-LFM-UILF can detect precisely the longitudinal distance of the electric conductivity gradients; (2) the signal-to-noise ratio of the reconstructed B-scan images of the electrical conductivity gradient distribution by the SECG-LFM-UILF are comparable to that obtained through the traditional SECG-UILF; and (3) using modulation frequency bandwidth of 2 MHz and modulation duration of 500 μs, a longitudinal resolution of 1 mm is achieved. For the scanning electric conductivity gradients with step-frequency ultrasound induced Lorentz force (SECG-SF-UILF), the in-phase demodulation scheme is simpler in hardware implementation than the IQ demodulation scheme but can only detect half of the longitudinal range. Experiments of SECG-SF-UILF are done on a sample of two-layer copper foil, which demonstrate that, using a frequency bandwidth of 2 MHz and 64 discrete frequencies, the longitudinal range of the sample can be detected precisely. The second part of the thesis studies the cross-correlation approach based elastography. To expand the frequency bandwidth of the shear wave displacement field so as to improve the quality of the shear wave velocity map, this part studies application of the Lorentz force for generation of shear wave fields. First, generation of shear wave sources on the soft medium surface through the mechanism of the Lorentz force is investigated by stimulating a non-ferromagnetic conductive ring or patch with a transient magnetic field. The origin and the frequency and amplitude characteristics of the Lorentz force acting on the conductive ring are confirmed by the displacement measurement using an interferometric laser probe. Under a transient magnetic field of changing rate of 10.44 kTs-1, the patch generates a shear wave field source of amplitude of 100 μm at the surface of the sample of polyvinyl alcohol (PVA) phantom. The shear wave fields created and propagating in the PVA phantom by experiments agree qualitatively well with the theoretical shear wave fields calculated through the analytical Green function solution. Then, the potential of the generated shear wave fields for the cross-correlation based shear wave velocity reconstruction is explored. Based on the cross-correlation approach, the qualitative shear wave velocity maps are reconstructed from 100 frames of the displacement fields, from which the interfaces or boundaries between regions of different stiffness can be clearly recognized, which are completely concealed in the ultrasound images
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Zhang, Shaobin. "High frequency magnetic field-induced strain of ferromagnetic shape memory alloys." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLY011.
Повний текст джерелаАнотація:
Les alliages à mémoire de forme ferromagnétique (FSMAs) possèdent la capacité d’accommoder une large déformation réversible à haute fréquence à l’aide d'une réorientation de la martensite induite par un champ magnétique. Cependant, cette réorientation à haute fréquence induit un frottement au niveau des interfaces entre les variantes de martensite provoquant une dissipation et par suite une élévation significative de la température dans le matériau, ce qui pose des problèmes d'instabilité nuisant à la performance du comportement dynamique des FSMAs. En particulier, l'amplitude de la déformation induite par le champ magnétique est réduite de façon significative lorsque l’augmentation de la température est suffisante pour déclencher la transformation de phase martensite-austénite. Un tel effet thermique sur les réponses dynamiques de FSMA n'a pas encore été étudié dans la littérature où la plupart des expériences dynamiques existantes ont été réalisées sur une courte période de temps (quelques secondes) afin d’éviter la variation de la température.Le but de cette thèse est l’analyse et la modélisation de ce phénomène. Pour ce faire, des analyses expérimentales et théoriques multi-échelles des performances des FSMAs soumis à un champ magnétique de longue durée et à haute fréquence sont réalisées.Tout d’abord, des expériences systématiques d'actionnement magnétique de longue durée (> 100 secondes) sur une éprouvette en monocristal Ni-Mn-Ga sont effectuées à différents niveaux de la fréquence du champ magnétique, de la contrainte de compression initiale et du flux d'air ambiant (échange de chaleur) afin d’étudier leur influence sur la réponse des FSMAs. Par ailleurs, un modèle unidimensionnel de transfert de chaleur a été est développé permettant d’interpréter les nouveaux phénomènes liés aux effets thermiques mises en lumière expérimentalement. Ainsi, les conditions nécessaires à l’obtention d’une réponse dynamique stable ont été déduites. De plus, afin de comprendre la dépendance de la déformation nominale induite par le champ magnétique par rapport aux échanges thermiques à partir d'une analyse microscopique, la distribution/évolution de la déformation locale ainsi que la transformation/réorientation associée parmi les différentes phases/variantes au cours de l'actionnement à haute fréquence sous divers conditions d'échange de chaleur sont analysées via des observations in-situ à l’aide la corrélation d'images numériques (DIC). Un nouveau mécanisme est ainsi révélé : le mouvement des interphases induit par la variation de température (transformation de phase) et le mouvement des variantes de martensite induit par le champ magnétique (réorientation de martensite) peuvent être activés simultanément, sous l'actionnement magnéto-thermique-mécanique (i.e, le champ magnétique à haute fréquence, la force de ressort mécanique et le flux d'air ambiant) dans la mesure où le matériau peut auto-organiser les fractions volumiques des différentes phases/variantes afin de satisfaire toutes les conditions aux limites thermo-magnéto-mécaniques. En outre, la morphologie des bandes de déformations et des différentes phases/variantes auto-organisées est révélée et expliquée à l’échelle microscopique à l’aide des conditions de compatibilité géométriqueFerromagnetic Shape Memory Alloys (FSMAs) have ability to provide large high-frequency reversible strain via magnetic field-induced martensite reorientation. But, the high-frequency frictional twin boundary motion of the martensite reorientation can induce a rapid accumulation of dissipation heat and cause a significant temperature rise in the material, which poses instability problems about the dynamic performance of FSMA. Particularly, the output strain amplitude would be reduced significantly when the temperature increases to be high enough to trigger the Martensite-Austenite phase transformation. However, such thermal effect on the dynamic responses of FSMA has not yet been investigated in literature where most existing dynamic experiments were performed only for a short-time period (a few seconds) to avoid the temperature variation. In this thesis, multi-scale experimental and theoretical analyses of the long-time performance of FSMA under high-frequency magnetic actuation are performed. Systematic experiments of the long-time magnetic actuation (> 100 seconds) on a Ni-Mn-Ga single crystal bar are conducted at various levels of magnetic field frequency, initial compressive stress and ambient airflow (ambient heat-exchange efficiency) to investigate their influences on the stable state of the high-frequency FSMA-actuator. A one-dimensional heat-transfer model is developed and the new experimental phenomena of the thermal effects are well understood. Based on the experimental results and theoretical analysis, critical conditions to achieve the large and stable output strain amplitude in the high-frequency actuation are derived. Moreover, to understand the heat-exchange dependence of the output nominal-strain from a microscopic view, the local strain distribution/evolution and the associated transformation/reorientation among the different phases/variants during the high-frequency actuation under various heat-exchange efficiencies are demonstrated via the in-situ Digital Image Correlation observations. A novel mechanism is revealed: the temperature-driven phase boundary motion (phase transformation) and the magnetic field-driven twin boundary motion (martensite reorientation) can be activated at the same time under the magneto-thermal-mechanical actuation (i.e., the high-frequency magnetic field, the mechanical spring force and the varying ambient airflow) as the material can self-organize its volume fractions of the different phases/variants to satisfy all the thermo-magneto-mechanical boundary conditions. Further, the self-organized morphology/pattern composed of various variants and phases during cyclic deformation (with the moving habit plane and twin boundaries) can be explained by microstructure compatibility analyses
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Arigong, Bayaner. "Space and Spectrum Engineered High Frequency Components and Circuits." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc801923/.
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With the increasing demand on wireless and portable devices, the radio frequency front end blocks are required to feature properties such as wideband, high frequency, multiple operating frequencies, low cost and compact size. However, the current radio frequency system blocks are designed by combining several individual frequency band blocks into one functional block, which increase the cost and size of devices. To address these issues, it is important to develop novel approaches to further advance the current design methodologies in both space and spectrum domains. In recent years, the concept of artificial materials has been proposed and studied intensively in RF/Microwave, Terahertz, and optical frequency range. It is a combination of conventional materials such as air, wood, metal and plastic. It can achieve the material properties that have not been found in nature. Therefore, the artificial material (i.e. meta-materials) provides design freedoms to control both the spectrum performance and geometrical structures of radio frequency front end blocks and other high frequency systems. In this dissertation, several artificial materials are proposed and designed by different methods, and their applications to different high frequency components and circuits are studied. First, quasi-conformal mapping (QCM) method is applied to design plasmonic wave-adapters and couplers working at the optical frequency range. Second, inverse QCM method is proposed to implement flattened Luneburg lens antennas and parabolic antennas in the microwave range. Third, a dual-band compact directional coupler is realized by applying artificial transmission lines. In addition, a fully symmetrical coupler with artificial lumped element structure is also implemented. Finally, a tunable on-chip inductor, compact CMOS transmission lines, and metamaterial-based interconnects are proposed using artificial metal structures. All the proposed designs are simulated in full-wave 3D electromagnetic solvers, and the measurement results agree well with the simulation results. These artificial material-based novel design methodologies pave the way toward next generation high frequency circuit, component, and system design.
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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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Atie, Elie. "Modeling of high electromagnetic field confinement metamaterials for both linear and non-linear applications." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2044/document.
Повний текст джерелаАнотація:
Notre recherche porte sur la réponse optique des nanostructures et nous sommes certainement intéressés à la modélisation de ces structures afin d'améliorer le confinement de la lumière. Ce confinement est un des paramètres qui conduisent à l'exaltation des effets optique linéaires et non linéaires, simultanément. Notre travail est divisé en deux sections, qui présentent deux effets optiques diffèrents basées sur le confinement des champs à l’intérieur du structure. Dans la première section, la réponse optique d’une nano-antenne à ouverture en forme de nœud papillon (BNA : Bowtie nano-aperture) sera étudiée en fonction de l’indice de réfraction du milieu. L’étude discute la variation de la longueur d’onde de résonance ainsi que l’intensité du champ confiné au milieu du gap de la BNA en fonction de la distance qui sépare l’antenne d’un substrat placé en face. L’étude prend le cas d’une BNA gravée au bout d’une fibre optique métallisée. Une étude numérique complète a été réalisée par des simulations numériques basées sur la méthode des différences finies FDTD-3D (Finite Difference Time Domaine – Three dimension). Le code utilisé est développé au sein du département d’Optique de l’Institut FEMTO-ST. Notre modèle numérique décrits bien la géométrie de l’antenne ainsi que la pointe. De même les propriétés optiques de la couche métallique de la sonde sont bien décrites à travers un modèle de dispersion (model de Drude). Une étude expérimentale a été réalisée en plus pour une validation des résultats collecte théoriquement, l’étude a considéré le cas de deux BNA avec des paramètres géométrique différents, néanmoins les résultats obtenues se correspond fortement aux résultats obtenues numériquement. Dans la deuxième partie, l'effet électro-optique des nanostructures sera étudié. L’effet électro-optique ou effet Pockels consiste d’une variation linéaire de l'indice de réfraction d'un milieu non-linéaire en fonction d'un champ électrique extérieur. Cependant, la variation est reliée au tenseur de susceptibilité non linéaire du deuxième ordre, ainsi, cette effet ce produit seulement dans les matériaux non-centrosymétrique. Dans notre étude les nanostructures sont fabrique avec le Niobate de Lithium (LN) qui est considéré comme le plus avantageux diélectrique pour l’exaltation des effets non linéaire grâce à ces propriétés (acousto-optique, électro-optique, piézoélectrique …). L’étude est complétée numériquement garce a des simulations basées sur la FDTD en tenant compte de la polarisation du champ. Au début, une validation de l’utilisation de la FDTD pour estimer l’effet électro-optique intrinsèque du LN a été achevée, l’étude considère un milieu homogène (pas de confinement des champs dans le milieu) qui a pour indice de réfraction celle du LN. Pour des structure qui présentes un confinement du champ plusieurs approximation ont été suggère dans cette partie. En outre, nous présentons un nouveau modèle auto-cohérent dans lequel la variation de l'indice de réfraction est modifiée au cours de la simulation. Plusieurs structure ont été discutés (réflecteur de Bragg, structure à cavité et 2D cristal photonique) qui présentent des facteurs de confinement différents. Une étude comparative entre les différentes méthodes, montre que la différence entre les résultats de chaque hypothèse devient plus important proportionnellement au facteur de confinementOur research is concerned with the optical response of nano-structures by modeling them in order to enhance the confinement of light in these structures, which leads to the exaltation of linear and nonlinear optical effects.Our work is divided into two sections, which are based on the enhancement of the electric field inside the structure. In the first section, we study the optical properties of a Bowtie Nano-aperture, BNA, as a function of the refractive index of the surrounding medium. The study discusses the variation of the resonance wavelength and the intensity of the enhanced field in the gap of the BNA as a function of the distance from a sample placed in front of our BNA. The BNA is engraved at the apex of a metallic coated fiber tip. In this section a theoretical study was achieved using the Finite Difference Time Domain method FDTD in which we implement a Drude dispersion model to faithfully describe the optical properties of metals. In addition, a validating experimental study was achieved and a high accordance between both results is recorded.In the second section, the electro optical effect of nano-structures is studied. Electro-optical effect or Pockels effect is the variation of the refractive index of a nonlinear media as a function of an applied external electric field. The electro-optical effect is a linear variation of the media refractive index. However it is also related to the second order nonlinear susceptibility tensor, thus it becomes a nonlinear effect that only occurs in non-centrosymetric material. In our study we chose the case of a nano-structure fabricated with Lithium Niobate. Lithium Niobate is widely used in photonic applications due to its electro-optical, acousto-optical and nonlinear optical properties. We present a theoretical study of the electro-optical effects using the FDTD simulation method. We started by approving the ability to use the FDTD to calculate the refractive index variation in bulk Lithium Niobate then we suggest different approximations to estimate the refractive index variation when the light is confined inside the structure. In addition we suggest a new self-consistent method in which the variation of the refractive index is modified during the simulation. The study shows a comparison between different assumptions (used in previous research) and the self-consistent method for various structures, like Bragg reflectors, cavity structures and 2D photonic crystals. The study shows that the difference between the results of each assumption becomes greater when the optical confinement in the structure becomes more important
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White, Ashley. "Novel High Frequency Electromagnetic Shielding Measurements Within Functional Geometries Using Non-Metal and Fatigued Conductors." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1501765571693941.
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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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Altarawneh, Moaz. "High frequency probes of superconductivity and magnetism in anisotropic materials in very high magnetic field." Tallahassee, Florida : Florida State University, 2009. http://etd.lib.fsu.edu/theses/available/etd-10142009-142552/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Florida State University, 2009.Advisor: James Brooks, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed on May 3, 2010). Document formatted into pages; contains xiii, 118 pages. Includes bibliographical references.