Dissertations / Theses: 'High frequency resonance method'

1

Bar, Galit 1970. "High-frequency time domain electron paramagnetic resonance : methods and applications." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17826.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.
Vita.
Includes bibliographical references.
There are numerous advantages to high frequency (high field) electron paramagnetic resonance (EPR) spectroscopy. Two of the most important are improved sensitivity and the improved resolution of field dependent interactions. In addition, there are many attractive features to time domain spectroscopy. Pulsed EPR allows for the design of experiments, which can specifically be used to study structure and dynamics of paramagnetic species and provide utmost resolution by separating interactions from each other. The combination of pulsed techniques and high frequencies is not only complimentary to continuous wave (CW) low frequency EPR but it also greatly increases the accessible information on paramagnetic species. High frequency, time domain EPR is still in its infancy. Spectrometers at W-band ([approximately] 95 GHz) are now available commercially but to date very few spectrometers operating at higher frequencies have been described. The spectrometer developed in the Francis Bitter Magnet Laboratory operates at a microwave (MW) frequency of 139.5 GHz corresponding to [approximately] 5 T magnetic field. The applications presented in this thesis illustrate the potential of high frequency, time domain EPR spectroscopy at 139.5 GHz in obtaining structural and mechanistic insights of several paramagnetic systems. Well resolved EPR spectra observed at 139.5 GHz of the stable tyrosine radical in ribonucleotide reductase (RNR) revealed the existence of a hydrogen bond in RNR from yeast, chapter 1. The bond length and orientation were determined from the nuclear frequencies of the proton, detected by orientation selective electron nuclear double resonance (ENDOR).
(cont.) The advantage of the time domain detection scheme is demonstrated in chapters 4, 5 and 6. A stimulated echo sequence is used to separate different organic radicals associated with the reduction chemistry and inhibition mechanisms of RNR. Using the dispersion in relaxation rates at high temperature ([approximately] 60 K) it is possible to filter the multi component spectrum. The assignment of new radicals is possible at high field, 5 T, due to the high resolution in g anisotropy. The findings support earlier proposals for the mechanism of nucleotide reduction and inhibition of this very important enzyme. To study photoexcited triplet molecules a light source was coupled to the high frequency spectrometer and the pulsed mode detection scheme was used to acquire EPR spectra. The new technique is demonstrated on several model systems. In addition to the basic advantages described above, high frequency EPR opens new frontiers for high spin systems, S >[or equal to] 1, with large spin-spin interaction. Because of the inverse field dependency of the zero field splitting, such systems may be totally EPR-silent at normal EPR frequencies. However their EPR spectra are accessible at high frequencies due to the reduction of linewidth. The Mn(II), S = 5/2, in superoxide dismutase (SOD) is a good example for such system.
by Galit Bar.
Ph.D.

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2

Peairs, Daniel Marsden. "High Frequency Modeling and Experimental Analysis for Implementation of Impedance-based Structural Health Monitoring." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27925.

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A promising structural health monitoring (SHM) method for implementation on real world structures is impedance-based health monitoring. An in-service system is envisioned to include on board processing and perhaps wireless transfer of data. Ideally, a system could be produced as a slap-on or automatically installed addition to a structure. The research presented in this dissertation addresses issues that will help make such a system a reality. Although impedance-based SHM does not typically use an analytical model for basic damage identification, a model is necessary for more advanced features of SHM, such as damage prognosis, and to evaluate system parameters when installing on various structures. A model was developed based on circuit analysis of the previously proposed low-cost circuit for impedance-based SHM in combination with spectral elements. When a three-layer spectral element representing a piezoceramic bonded to a base beam is used, the model can predict the large peaks in the impedance response due to resonances of the bonded active sensor. Parallel and series connections of distributed sensor systems are investigated both experimentally and with the developed model. Additionally, the distribution of baseline damage metrics is determined to assess how the large quantities of data produced by a monitoring system can be handled statistically. A modification of the RMSD damage metric has also been proposed that is essentially the squared sum of the Z-statistic for each frequency point. Preferred excitation frequencies for macro-fiber composite (MFC) active sensors are statistically determined for a long composite boom under development for use in rigidizable inflatable space structures.
Ph. D.

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3

Бондаренко, И. Н., В. А. Николаенко, and А. В. Полищук. "The cavity with the Tunnel Diodes and Corbino-Electrodes for Analyze Dielectrics and Semiconductors." Thesis, Sumy State University, 2019. http://openarchive.nure.ua/handle/document/10409.

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. Study of nano structures is importance as bind the nanotechnology and applying. Many methods and tools use here (EPA); (NMR); AFM, X-ray so on. The high frequency (HF) resonance method at low temperature is sensitive and exact method because high quality of resonance and neglecting both the device noise and losses in matter. The “gaga – nano” conception take a place here too. The using little tunnel diodes as the generator and the detector in cavity is ideal for that aim. In this project cavity bottom is system of coaxial insulated rings (Corbino geometry) which applied as the low frequency (LF) analyzer as well as the modulator of HF field. So, we proposed HF - LF mini- analyzer for study of matter, the composition of device is given.

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Menon, K. Rajalakshmi. "Application Of High Frequency Natural Resonances Extracted From Electromagnetic Scattering Response For Discrimination Of Radar Targets With Minor Variations." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/159.

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Radars, as the name suggests, were traditionally used for Radio Detection and Ranging. Nevertheless, advances in high resolution electromagnetic simulations, Ultra Wide-Band sources, signal processing and computer technologies have resulted in a possible perception of radars as sensors for target discrimination. In this thesis, the feasibility of discrimination between targets even with minor variations in structure and material composition on the basis of radar echoes is effectively demonstrated. It is well-known that the echoes from any target are affected by its natural frequencies which are dependent only on the shape and material composition of the target, and independent of the aspect angle or the incident waveform. The E-pulse technique is based on the fact that incident waveforms can be designed that uniquely annihilate the echoes from chosen regions of a target, and forms the basis of the method of discrimination proposed in this thesis. Earlier methods reported in the literature, effectively discriminated only between different classes of targets with substantial variations in the overall dimensions of the body. Discrimination of targets of the same class with a minor structural modification or with a material coating on specific areas was rather difficult. This thesis attempts and successfully validates a method which comprehensively addresses this problem. The key idea of this method is to use the higher frequency resonances (which characterise the finer details of a target) in the E-pulse technique. An obviously important aspect of target discrimination is therefore that of precisely estimating the natural frequencies for each target and understanding the changes in these frequencies, and their associations with the changes in structure and material composition. Current approaches to determine these frequencies are either based In the time or frequency domains. While the latter approach comprises the computation of the roots of a related determinantal equation, in the time domain, the natural frequencies are extracted from the response of a target to an impulse. Such a response can either be generated from actual experiments or by simulating the scattering response using Computational Electromagnetic (CEM) techniques. In this work, the impulse response is obtained from the frequency response of the scatterers in the frequency range of interest. Since no single CEM technique can effectively cover the entire range of frequencies needed for the E-Pulse synthesis. The Method of Moments and Physical Optics have been used for low and high frequency scattering respectively. The results obtained using the latter technique are validated by comparing with those obtained using Method of Moments at the transition frequencies and Geometrical Theory of Diffraction (GTD). The natural frequencies (i.e., poles of a corresponding transfer function) are extracted from the impulse response using Prony's algorithm. One of the parameters in this method is the number of such poles (i.e.. the order of the transfer function) present in the response, and the accuracy of the computed pole values depends on this assumed order. Here, the Hankel singular values of a transfer function is used to estimate the number of poles. This in turn implies that a specific norm of the error between a transfer function corresponding to the frequency response generated earlier, and a transfer function with an assumed order obtained using Prony's method is minimised. In the thesis, a wide range of target shapes are considered for purposes of illustration: wires, cylinders, spheres, plates and complex bodies such as aircraft, and the discrimination capability is demonstrated by introducing minor perturbations in their shape and/or material composition. .The following cases are considered here: (a) Wires: Conducting wires with a protrusion in one segment; conducting wire from another coated with a dielectric in a segment, (b) Cylinders: Conducting cylinders with one perturbed; conducting cylinders with a portion scrapped off in the middle, (c) Plates: Conducting plates with a elongation on one comer; conducting plate with another one with a hole in the centre, (d) Spheres: Conducting spheres with different radii; conducting spheres with Radar Absorbing Material coated spheres with different coating thickness; conducting spheres with chiral coated spheres with varying coating thickness, (e) Aircraft: Canonical model of MiG-29 aircraft from a similar one with stores placed under the wing.

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Magill, Arthur W. "Ultra-high frequency magnetic resonance imaging." Thesis, University of Nottingham, 2007. http://eprints.nottingham.ac.uk/10740/.

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This thesis addresses the problem of radiofrequency probe design for Ultra High Frequency Magnetic Resonance Imaging (7T). The signal-to-noise ratio available in Magnetic Resonance Imaging (MRI) is determined by the static magnetic field strength, causing a continued drive toward higher fields to enable faster image acquisition at finer spatial resolution. The resonant frequency increases linearly with static field strength. At 7T the proton resonant frequency is 300MHz, with a wavelength of approximately 13cm in tissue. As this is smaller than the dimensions of the human head, the phase of the radiofrequency (RF) signal varies considerably across the sample, producing field cancellation due to interference. A full wave electromagnetic simulator, using the Transmission Line Matrix (TLM) method, was developed to investigate RF probes at high frequency. A Birdcage probe operating at 64, 128 and 300MHz (corresponding to 1.5, 3 and 7T) was simulated, loaded with an anatomically detailed human head model. A half-wave microstrip was investigated for use as a high frequency probe element. Magnetic and electric fields produced by a single microstrip were simulated, and the strip dimensions varied to investigate the effect on field penetration into the head and Specific Absorption Rate (SAR). A transmit-receive array probe using four microstrip elements was then developed. Bloch simulations were run, using TLM generated magnetic fields, to investigate imaging at short wavelength. Parallel receive probes are demonstrated to offer considerable advantage over volume probes, as signals from receive elements can be combined without interference. There is no transmit equivalent to parallel reception; simultaneous excitation of independent probe elements causes interference in exactly the same manner as a volume probe. A new imaging sequence was developed using a Burst-like encoding to allow sequential excitation of probe elements, without interference, which can be recalled in a single readout. An improvement in image homogeneity was demonstrated, and SENSE acceleration of the new imaging sequence is shown. The sequence was implemented at 3T using a purpose built four element microstrip probe. An RF multiplexer was also built to enable transmit element switching during the imaging sequence. It was demonstrated that images due to different RF excitations, acquired in a single EPI readout, can be separated.

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Gasson, Julia. "Radio-frequency coils for high-resolution magnetic resonance imaging." Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262503.

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Zhang, Yang 1964. "Radio frequency gradient high resolutions nuclear magnetic resonance spectroscopy." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39054.

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8

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.

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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.

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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/.

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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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Bellew, Brendan Francis. "High frequency (139.5 GHz) electron paramagnetic resonance spectroscopy of biomolecules." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38758.

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11

Srivastava, Abhishek. "High Frequency Study of Magnetic Nanostructures." ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1530.

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The work in this thesis is divided in three parts. In part one we developed electrodeposition method of Nickel Nanowire in commercial AAO template in constant current (Galvanostatic) mode, further we tried to estimate the growth rate from theory, from saturation magnetization and direct measurement from SEM image. In part two we focused on using the Vector Network Analyzer (VNA) to measure the Ferromagnetic Resonance (FMR))of various magnetic Nanowire arrays. We employed different measurement geometries using microstripline and coplanar waveguide as microwave transmission lines. In part three our aim was to study the magnetic properties of complex ferromagnetic system, especially the effect of interactions on dynamic properties of magnetic nanostructures (nanowire arrays and exchange biased ferromagnetic-antiferromagnetic multilayers). Our effort was centered on using ferromagnetic resonance to understand the dynamic response of these systems.

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12

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.

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13

Skutt, Glenn R. "High-Frequency Dimensional Effects in Ferrite-Core Magnetic Devices." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30596.

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MnZn ferrites are widely used in power electronics applications where the switching frequency is in the range of several tens of kilohertz to a megahertz. In this range of frequencies the combination of relatively high permeability and relatively low conductivity found in MnZn ferrite helps to minimize the size of magnetic devices while maintaining high efficiency. The continuing improvement in semiconductor switches and circuit topologies has led to use of high-frequency switching circuits at ever increasing power levels. The magnetic devices for these high-power, high-frequency circuits require magnetic CORES that are significantly larger than standard ferrite-core devices used at lower power levels. Often such large ferrite cores must be custom designed, and at present this custom design is based on available material information without regard for the physical size of the structure. This thesis examines the issues encountered in the use of larger MnZn ferrite cores for high-frequency, high-power applications. The two main issues of concern are the increased power dissipation due to induced currents in the structure and the change in inductance that results as the flux within the core is redistributed at higher frequencies. In order to model these problems using either numerical or analytical methods requires a reliable and complete set of material information. A significant portion of this work is devoted to methods for acquiring such material information since such information is not generally available from the manufacturers. Once the material constants required for the analysis are determined, they are used in both closed-form and numerical model to illustrate that large ferrite cores suffer significant increases in loss and significant decreases in inductance for frequencies as low as several hundred kilohertz. The separate impacts of the electrical and magnetic losses in the core are illustrated through the use of linear finite element analyses of several example core structures. The device impedances calculated using the FEA tools show fair agreement with measurement. An analysis of gapped structures and segmented cross-sections shows that these design options can reduce the severity of the dimensional problems for some designs.
Ph. D.

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Davies, S. J. "Frequency-selective excitation and non-linear data processing in nuclear magnetic resonance." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233510.

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Procházka, David. "Vytvoření předpokladů pro hodnocení vlastností vysokopevnostních betonů s využitím nedestruktivních metod zkoušení." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-233795.

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High-strength concrete (HSC) belongs in the recent years to frequently used types of concrete. It allows realization of static challenging structures and also shows due to its dense structure greater durability especially against aggressive media. Currently HSC construction realization abroad is not exceptional. It’s using in the Czech Republic is still limited. When realized, then in a small scale in civil engineering works. The realization of high-strength concrete structures is closely related with the concrete construction quality verification. Good efficiency of the quality control methods can provide non-destructive testing methods (NDT), especially when investigating strength of concrete built in structure. A lack on relevant data for non-destructive testing of HSC in technical and normative rules is to be considered as a significant deficiency. Evident for HSC generally is the lack in literature on deeper analysis of the factors affecting their non-destructive testing, as well a meaningful methodology or practically usable calibration relationships. HSC differs from ordinary concrete not only by used components, but also by more compact structure with different strength – elastic characteristics. Considering these differences, HSC strength prediction can not be performed by using calibration relationships developed for ordinary concrete. Moreover, the question is to what extent the current knowledge of the NDT results influencing factors can be considered as valid. The paper presents findings on the effects of the key factors affecting the measurement results of Schmidt hardness method and ultrasonic pulse method, including recommendations for the practical application of these methods. The problematic of static vs. dynamic modulus of elasticity was also solved. Calibration equations for predicting the compressive strength of HSC from the non-destructive testing parameter were elaborated, showing high cohesion among variables and practically usability.

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Mei, Chang-Sheng. "Accelerated MR Thermometry for High Intensity Focused Ultrasound Therapy." Thesis, Boston College, 2011. http://hdl.handle.net/2345/2425.

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Thesis advisor: Michael Graf
The purpose of this dissertation was to investigate the temporal limit on the ability to measure temperature changes using magnetic resonance imaging (MRI). The limit was examined in experiments using a variety of imaging techniques for MRI-based temperature measurements. We applied these methods for monitoring temperature changes in focused ultrasound (FUS) heating experiments. FUS is an attractive alternative to surgical resection due to its noninvasive character. FUS treatments have been successfully conducted in several clinical applications. MRI and MR thermometry is a natural choice for the guidance of FUS surgeries, given its ability to visualize, monitor, and evaluate the success of treatments. MR thermometry, however, can be a very challenging application, as good resolution is often needed along spatial, temporal as well as temperature axes. These three quantities are strictly related to each other, and normally it is theoretically impossible to simultaneously achieve high resolutions for all axes. In this dissertation, techniques were developed to achieve this at cost of some reduction in spatial coverage. Given that the heated foci produced during thermal therapies are typically much smaller than the anatomy being imaged, much of the imaged field-of-view is not actually being heated and may not require temperature monitoring. By sacrificing some of the in-plane spatial coverage outside the region-of-interest (ROI), significant gains can be obtained in terms of temporal resolution. In the extreme, an ROI can be chosen to be a narrow pencil-like column, and a sampling time for temperature imaging is possible with a temporal resolution of a few milliseconds. MRI-based thermal imaging, which maps temperature-induced changes in the proton resonance frequency, was implemented in two projects. In the first project, three previously described, fast MR imaging techniques were combined in a hybrid method to significantly speed up acquisition compared to the conventional thermometry. Acceleration factors up to 24-fold were obtained, and a temporal resolution as high as 320 milliseconds was achieved. The method was tested in a gel phantom and in bovine muscle samples in FUS heating experiments. The robustness of the hybrid method with respect to the cancellation of the fat signal, which causes temperature errors, and the incorporation of the method into an ultrafast, three dimensional sequence were also investigated. In the second project, a novel MR spectroscopic sequence was investigated for ultrafast one-dimension thermometry. Temperature monitoring was examined during FUS sonications in a gel phantom, SNR performance was evaluated in vivo in a rabbit brain, and feasibility was tested in a human heart. It was shown capable in a FUS heating experiment in a gel phantom of increasing temporal resolution to as high as 53 milliseconds in a three Tesla MRI. The temporal resolution achieved is an order of magnitude faster than any other rapid MR thermometry sequences reported. With this one-dimensional approach, a short sampling time as low as 3.6 milliseconds was theoretically achievable. However, given the SNR that could be achieved and the limited heating induced by FUS in the gel phantom in a few milliseconds, any temperature changes in such a short period were obscured by noise. We have analyzed the conditions whereby a temporal resolution of a few-milliseconds could be obtained
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

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Taylor, Paul. "Observation of an ultra-high Q resonance in a single ion of '1'7'2Yb'+." Thesis, University of London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337596.

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18

Kauffman, John Gabriel. "Design of a High Impedance Preamplifier for Coil Arrays." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050205-141036/.

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Gao, Kai. "A Study in the Frequency Warping of Time-Domain Methods." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32331.

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This thesis develops a study for the frequency warping introduced by time-domain methods. The work in this study focuses first on the time-domain methods used in the classical SPICE engine, that is the Backward Euler, the Trapezoidal Rule and the Gear's methods. Next, the thesis considers the newly developed high-order method based on the Obreshkov formula. This latter method was proved to have the A-stability and L-stability properties, and is therefore robust in circuit simulation. However, to the best of the author's knowledge, a mathematical study for the frequency warping introduced by this method has not been developed yet. The thesis therefore develops the mathematical derivation for the frequency warping of the Obreshkov-based method. The derivations produced reveal that those methods introduce much smaller warping errors than the traditional methods used by SPICE. In order to take advantage of the small warping error, the thesis develops a shooting method framework based on the Obreshkov-based method to compute the steady-state response of nonlinear circuits excited by periodical sources. The new method demonstrates that the steady-state response can be constructed with much smaller number of time points than what is typically required by the classical methods.

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Ogundapo, Olusegun. "High frequency Ethernet cabling analysis and optimization." Thesis, De Montfort University, 2016. http://hdl.handle.net/2086/14148.

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This thesis provides analytical and forensic tools for data cabling, with particular focus on Ethernet cabling to assist designers and those involved in deployments in analyzing cable performance and the reasons behind the actual performance obtained. The need for higher bandwidth to accommodate increasing demand for multimedia services and data centers network infrastructure led to the formation of IEEE P802.3bq to create standards for 40GBASE-T over twisted pair cables. The 40GBASE-T is expected to offer bandwidth of up to 2000MHz over a maximum channel length of 30m. The research investigated means of predicting key performance parameters in Ethernet cabling standardization using the 40GBASE-T as an example. The performance parameters prediction method provided is equally applicable to ongoing and future high data rate Ethernet cabling standardization such as the 2.5/5GBASE-T and 50/100GBASE-T. Another problem in the Ethernet networking world is the availability of counterfeit and non-standards compliant twisted pair cables in the market. The significant amount of communications cables in the market containing copper clad aluminum cable or other non-standards compliant conductors disguised as Category 6 cables can pose serious problems to companies’ networks, the contractors or the installers. This is in view of the growing demand for internet of things (IOT) services that makes it imperative to have a reliable Ethernet driven communication network to support the required infrastructure. This thesis therefore, provides techniques that can be used to evaluate cables key performance parameters using the Feature Selective Validation method and the Kolmogorov-Smirnov (KS) test. The technique can help engineers avoid subjective judgement and make objective decisions in the selection of cables. The research provided a technique that can be used to reverse engineer impedance profile from the return loss measurement of Ethernet cables using genetic algorithms. The method can be applied in situations where time domain tests are inaccessible or only simple (magnitude) tests in the frequency domain are available and there is the need for impedance profiles of cables to evaluate their performance or physical integrity before or after installation. The method can also be useful where only simple (magnitude) tests are the only historical data available for the cables and facilities for time domain reflectometry measurements are inaccessible. This research also presented a method of evaluating and predicting NEXT in unshielded twisted pair (UTP) using Category 6 cables as an example. The results obtained from the evaluation were used to provide crosstalk parameters for fast NEXT prediction in Category 6 (UTP) cables. The research used the measured NEXT of three Category 6 (UTP) cables from different manufacturers for evaluation and validation. The evaluation and modeling method can thus be useful to engineers investigating NEXT in the design of data communication systems.

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Stefan, Anca Irina. "Modeling and design of resonators for electron paramagnetic resonance imaging and ultra high field magnetic resonance imaging." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1133293403.

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Schrama, Judith Marije. "High-frequency magneto-conductivity studies of low-dimensional organic conductors." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365779.

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Popernack, Thomas G. Jr. "Development of a data reduction method for a high frequency angle probe." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45881.

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A data reduction method has been developed and tested for a high frequency angle probe. The angle probe is designed for unsteady aerodynamic measurements in transonic cryogenic wind tunnels. The probe measures time-resolved total pressure, static pressure, angle of attack, and yaw angle from readings of four pressure transducers. The unique feature of this probe, as compared to a conventional multi-hole directional probe, is that the four high frequency response silicon pressure transducers are mounted flush on the probe tip. The data reduction method is basically an interpolation routine of calibration curves. The calibration curves consist of experimentally determined non-dimensional flow coefficients.

Two experiments were conducted to test the probe and the data reduction method. The first experiment tested the angle probe in a Karman vortex street shed from a cylinder. In the second experiment, the angle probe was placed in an open air jet with an exit Mach number of 0.42. Plots of the time-resolved measurements and the Fast Fourier Transform analysis were made for each test.
Master of Science

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Gunamony, Shajan [Verfasser], and Klaus [Akademischer Betreuer] Scheffler. "Radio Frequency Coils for Ultra-high Field Magnetic Resonance Imaging / Shajan Gunamony ; Betreuer: Klaus Scheffler." Tübingen : Universitätsbibliothek Tübingen, 2016. http://d-nb.info/1163665169/34.

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Barnes, Andrew Charles. "Characterization of High-Aspect Ratio, Thin Film Silicon Carbide Diaphragms Using Multimode, Resonance Frequency Analysis." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1414844482.

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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.

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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.

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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.

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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.

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Lesser, Beverly Brown. "Thermal-magnetic finite element model of a high frequency transformer." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/44121.

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In high-frequency power transformers, magnetic material properties cannot be assumed to be constant. These properties vary with frequency, temperature, and magnetic flux density. Heat generation is, in turn, a function of the magnetic permeability, magnetic flux density, and frequency. Current design methods are either empirical or based on linear, uncoupled models. To better understand the relationship between heat transfer, magnetic flux density, material properties, and core geometry in a miniature, high-frequency transformer, a finite-element program has been developed to solve the coupled thermal-magnetic equations for an axisymmetric transformer. The program accounts for nonlinear temperature and magnetic field dependent material properties, geometry, and driving frequency.

The program, HT-MAG, is based on a series of derived magnetic field equations. The Ritz method is applied to the magnetic and thermal equations in the development of the program. The program alternately solves the finite element approximations to the thermal and magnetic governing equations until the magnetic properties match within a specified fraction or a maximum number of iterations are performed. In addition, the program can be linked with existing pre- and post-processors or can accept manual pre- and post-processing.

Six test cases were run to test the validity of the program. The first two cases tested the uncoupled heat transfer calculations. One of these tested the thermal conduction calculations while the other tested the heat generation calculations. The next two cases tested the uncoupled magnetic equations. The first was a direct current (DC) case, while the second was an alternating current (AC) case. The final two cases tested the thermal magnetic coupling. Solutions to these cases are presented and discussed.

Master of Science

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Shiroishi, Jason William. "Bearing condition diagnostics via multiple sensors using the high frequency resonance technique with adaptive line enhancer." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17779.

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Vesselle, Hubert. "High-frequency electromagnetic effects and signal-to-noise ratios of surface coils for magnetic resonance imaging." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1059060235.

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Abolmoali, Philip. "Spectral Energy Transfers in Transonic Cavity Flows with High Frequency Flow Control from Powered Resonance Tubes." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511867795447293.

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Rouse, Jerry Wayne. "Energy-Based Boundary Element Method for High-Frequency Broadband Sound Fields in Enclosures." NCSU, 2000. http://www.lib.ncsu.edu/theses/available/etd-20000911-161316.

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This work sets forth a new method for predicting the spatialvariation of mean square pressure within two-dimensionalenclosures containing high-frequency broadband sound fieldsand light to moderate absorption. In the new method, theenclosure boundaries are replaced by a continuousdistribution of broadband uncorrelated sources, each ofwhich provides a constituent field expressed in terms ofmean square pressure and time average intensity variables.Superposition of these fields leads to the overall meansquare pressure and time average intensity as a function ofposition. Boundary conditions for radiating and absorbingsurfaces are recast in terms of energy and intensityvariables. The approach is implemented as a boundaryelement formulation for efficient evaluation of the pressureand intensity fields in enclosures. In contrast totraditional boundary element methods, the new method isindependent of frequency. A two-dimensional model problemenclosure is investigated to verify the new method. The exact analytical solution for the mean square pressuredistribution within the model problem enclosure is obtainedand compared to the results predicted by the new method.The comparisons indicate that the new method is asignificant improvement upon classical diffuse field theoryand computationally efficient relative to traditional boundary element methods and ray tracing techniques.

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Sanaie, Ramin Carleton University Dissertation Engineering Electronics. "Fast method for frequency and time domain simulation of high-speed VLSI interconnects." Ottawa, 1994.

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Attari, Amir Reza. "Analysis of interference in high frequency circuits using the transmission line matrix method." Université Joseph Fourier (Grenoble), 2002. http://www.theses.fr/2002GRE10056.

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Dans la compatibilité électromagnétique (CEM) l'analyse des interférences est très importante. Plusieurs progrès technologiques tels que les processeurs ultrarapides et le packaging à faible coût ont contribué à l'importance de cette analyse. La recherche réalisée ici établit une méthode hybride efficace pour l'analyse des interférences. Cette méthode hybride est basée sur la méthode TLM (transmission line matrix) et la formulation des équations intégrales dans le domaine temporel. La démarche employée dans l'étude est la suivante: La méthode TLM est utilisée pour analyser chaque circuit séparement puis les équations intégrales dans le domaine temporel sont mises en oeuvre pour déterminer le rayonnement des circuits et les interférences entre ces derniers. La méthode hybride proposée est très efficace pour des structures qui contiennent des circuits séparés par de grandes distances. A l'inverse de l'application classique de la méthode TLM, la mémoire et le temps de calcul de cette nouvelle méthode son indépendants de la distance entre les circuits. Le blindage par boitiers électromagnétiques est fréquemment employé pour réduire l'émission ou pour améliorer l'immunité des circuits électroniques aux interférences hautes fréquences. Dans cette étude, la méthode TLM est également utilisée pour analyser et concevoir des boitiers électromagnétiques. Le blindage considéré est un boitier rectangulaire avec une ouverture de forme arbitraire. La méthode hybride TLM-Equations intégrales est aussi utilisée pour estimer l'interférence entre deux circuits protégés respectivement par des boitiers de blindage. Des mesures expérimentales sont fournies pour valider les résultats des simulations numériques présentées dans cette thèse.

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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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Inoa, Ernesto. "A New High-Frequency Injection Method for Sensorless Control of Doubly-Fed Induction Machines." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338345508.

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Haemer, Gillian. "Optimizing Radio Frequency Coil Performance for Parallel Magnetic Resonance Imaging at Ultra High Field| Evaluation and Optimization of Integrated High Permittivity Materials." Thesis, New York University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10751718.

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In the time since magnetic resonance imaging (MRI) was introduced, scientific progress has allowed for a factor-of-ten increase in static magnetic (B₀) field strength, and has developed MR into a clinical workhorse. This increase in B₀ field strength has the potential to provide significant gains to the inherent signal-to-noise ratio of resulting images. However, this progress has been limited by degradations in the spatial homogeneity of the radiofrequency magnetic fields used for nuclear excitation (B₁), which have wavelengths comparable to the dimensions of the human body in modern high-field MRI. Techniques to improve homogeneity, including B₁-shimming and parallel transmission, require multi-element radiofrequency (RF) transmit arrays. Increasing B₀ field strength is also associated with an increase in the deposition of RF energy into the subject, clinically measured and regulated as Specific energy Absorption Rate (SAR), deposited in tissue during image acquisition. High permittivity materials (HPMs) have the potential to augment RF coil performance outside of B₁-shimming or parallel transmission methods. The use of HPM pads placed in existing RF coils has also been shown to provide a potential reduction of array SAR in nuclear excitation, as well as potential performance benefits in signal reception. However, the question of how best to strategically use these materials in the space between the coil and the sample in order to maximize benefit and alleviate any potential problems has not yet been thoroughly addressed.

The contributions presented in this dissertation demonstrate the potential utility of the integration of HPMs into transmit-receive RF coils, as an integral component of the hardware design. A framework to quickly choose the relative permittivities of integrated materials, optimized relative to an absolute standard (rather than relative to a different design) is introduced, and used to demonstrate that readily available material properties can provide significant improvements in multi-element transmit performance. A subsequent analysis of practical effects and limitations of these materials on the RF coil resonance properties is performed, including the description of a unique adverse resonance splitting phenomenon and how to avoid it. A transmit/receive RF coil design is built and evaluated, first on its own experimentally, and then in simulation with a helmet-shaped high permittivity material former to examine the benefits and challenges associated with HPM integration into RF coils.

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Van, Niekerk Adam Marthinus Johannes. "A vector based approach for high frequency prospective correction of rigid body motion in Magnetic Resonance Imaging (MRI)." Doctoral thesis, Faculty of Health Sciences, 2019. http://hdl.handle.net/11427/30093.

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Magnetic Resonance Imaging (MRI) is remarkable in that it is possible to obtain image resolutions much smaller than the wavelength of the radiated signal. This is achieved through the use of specialised gradient coils that linearly manipulate the magnitude of the magnetic field within the imaging volume. The instantaneous signal received from the subject represents a periodically varying map based on the duration and magnitude (moment) of the previously applied gradient fields. Representing an object as the sum of periodic maps is difficult and as a result many unique gradient moments are required to form an image. When the subject moves the periodic maps are no longer coherent and the constructive/destructive interference becomes invalid. The artefacts are dependent on how and when motion occurred, and manifest as ghosting, ringing and blurring of the image. This thesis describes a novel approach to measuring and correcting for motion as the data are acquired. A small device was constructed that combines observations from a magnetometer (static magnetic field [z]) and an accelerometer (earth’s gravitational field [y]) with an angular rate sensor to determine its orientation with respect to the imaging coordinate frame (VectOrient). It was precise enough to track the subject’s heart beat and breathing and accurate to within one degree. A gradient field probe was then designed for position encoding. The probe measured the rate of change of the gradient magnetic fields using three mutually orthogonal pickup coils. Assuming linear gradients and using Maxwell’s equations, with negligible rates of change of curl and divergence, it was possible to accurately model the three dimensional vector fields that the gradients produce, eliminating the need for a laborious manual calibration. Sub-microsecond synchronisation was achieved by detecting radio frequency pulses in the imaging sequence with a small resonant circuit. This combined with a 2.4 GHz radio link enabled the probe to be wireless. Finally, the pickup coil observations were combined with the vector based orientation estimates and the gradient field model to achieve efficient multidimensional position, orientation and inter-gradient-delay encoding with a 880 µs pulse sequence insert. The Wireless Radio frequency triggered Acquisition Device (WRAD) tracks involuntary and deliberate subject motion, improving image quality without scanner specific calibration.

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Groitl, Felix [Verfasser], and D. Alan [Akademischer Betreuer] Tennant. "High Resolution Spectroscopy with the Neutron Resonance Spin Echo Method / Felix Groitl. Betreuer: D. Alan Tennant." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2013. http://d-nb.info/1030099715/34.

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Yilmazel, Canan. "Analysis Of High Frequency Behavior Of Plate And Beam Structures By Statistical Energy Analysis Method." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605133/index.pdf.

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Statistical Energy Analysis (SEA) is one of the methods in literature to estimate high frequency vibrations. The inputs required for the SEA power balance equations are damping and coupling loss factors, input powers to the subsystems. In this study, the coupling loss factors are derived for two and three plates joined with a stiffener system. Simple formulas given in the literature for coupling loss factors of basic junctions are not used and the factors are calculated from the expressions derived in this study. The stiffener is modelled as line mass, Euler beam, and open section channel having double and triple coupling. Plate is modelled as Kirchoff plate. In the classical SEA approach the joint beam is modelled as another subsystem. In this study, the beam is not a separate subsystem but is used as the characteristics of the joint and to calculate the coupling loss factor between coupled plates. Sensitivity of coupling loss factors to system parameters is studied for different beam approaches. The derived coupling loss factors and input powers are used to calculate the subsystem energies by SEA. The last plate is joined to the first one to simulate the fuselage structure. A plate representing floor structure and acoustic volume are also added. The different modelling types are assessed by applying pressure wave excitation. It is shown that deriving the parameters as given in this study increases the efficiency of the SEA method.

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Laursen, Kirk Garrett. "A method of determining the high frequency dielectric properties of thin films using in-situ structures." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/13844.

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Cooper, Simon. "A frequency response method for sensor suite selection with an application to high-speed vehicle navigation." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318591.

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Tye, Thomas N. "Application of digital signal processing methods to very high frequency omnidirectional range (VOR) signals in the design of an airborne flight measurement system." Ohio University / OhioLINK, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1177702951.

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Malherbe, Chanel. "Fourier method for the measurement of univariate and multivariate volatility in the presence of high frequency data." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/4386.

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Luo, Haoming. "High frequency thermomechanical study of heterogeneous materials with interfaces." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI130.

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Le transfert de chaleur est intimement lié à la propagation du son (transfert acoustique) dans les matériaux, par exemple dans les isolants et les semi-conducteurs, les principaux vecteurs d’énergie sont des phonons acoustiques. Le concept de présence d’interfaces a été largement exploité pour manipuler efficacement les phonons des longueurs d’onde macroscopiques aux longueurs d’onde nanométriques. Les derniers correspondent aux fréquences en régime THz, qui sont responsables du transport thermique à température ambiante. Dans cette thèse, la méthode des éléments finis est utilisée pour effectuer des analyses transitoires de la propagation des paquets d’ondes dans différents milieux à 2D. Elle est commencée par une étude paramétrique de l’atténuation des paquets d’ondes dans un système élastique semi-infini avec des interfaces circulaires périodiques. Trois paramètres clés sont étudiés, notamment le contraste de rigidité, la densité d’interface et la longueur d’onde des phonons. Différents régimes de transfert (propagatif, diffusif et localisé) sont identifiés, qui permettent d’identifier la contribution des phonons à la conductivité thermique. Outre les interfaces circulaires, la réponse mécanique et l’atténuation acoustique pour différents types d’interfaces sont également étudiées, telles que l’inclusion de forme dendritique, l’inclusion d’Eshelby, et les matériaux poreux avec des pores ordonnés / désordonnés. Afin d’étendre l’étude aux matériaux amorphes, j’ai également considéré un milieu hétérogène avec des rigidités aléatoires réparties dans l’espace selon une distribution gaussienne basée sur la théorie de l’élasticité de cisaillement hétérogène des verres. Enfin et surtout, deux versions de lois de comportement viscoélastiques sont proposées pour prendre en compte l’atténuation intrinsèque des phonons dépendant de la fréquence dans les verres, dans le but qu’un milieu visqueux homogène puisse reproduire cette atténuation intrinsèque. La simulation par éléments finis confirme qu’un modèle continu peut suivre strictement l’atténuation atomistique (G) avec une loi de comportement viscoélastique linéaire macroscopique bien calibrée. Par rapport aux données expérimentales de a-SiO2, notre deuxième loi de comportement reproduit qualitativement et quantitativement les trois régimes d’atténuation acoustique en fonction de la fréquence : successivement Γ ∝ ω^2,ω^4,ω^2
Heat transfer is actually intimately related to the sound propagation (acoustic transfer) in materials, as in insulators and semi-conductors the main heat carriers are acoustic phonons. The concept of the presence of interfaces has been largely exploited for efficiently manipulating phonons from long-wavelength to nanometric wavelengths, i.e., frequencies in THz regime, responsible for thermal transport at room temperature. In this thesis, the finite element method is used to perform transient analysis of wavepacket propagation in different mediums. I started with a parametric study of attenuation of acoustic wave-packets in a 2D semi-infinite elastic system with periodic circular interfaces. Three key parameters are investigated, including rigidity contrast, interface density and phonon wavelength. Different energy transfer regimes (propagative, diffusive, and localized) are identified allowing to understand the phonon contribution to thermal transport. Besides the circular interfaces, mechanical response and acoustic attenuation for different types of interfaces are also investigated, such as Eshelby’s inclusion, dendritic shape inclusion and porous materials with ordered/disordered holes. In order to extend the study to amorphous materials, I also considered a heterogeneous medium with random rigidities distributed in space according to a Gaussian distribution based on the theory of heterogeneous shear elasticity of glasses. Finally yet importantly, viscoelastic constitutive laws are proposed to take into account the frequency-dependent intrinsic phonon attenuation in glasses, with the aim of reproducing such intrinsic attenuation using a homogeneous viscous medium. Finite element simulation confirms that a continuum model may strictly follow the atomistic attenuation (G) for a well-calibrated macroscopic linear viscoelastic constitutive law. Compared with the experimental data in a-SiO2, our second constitutive law reproduces qualitatively and quantitatively the three regimes of acoustic attenuation versus frequency : successively Γ∝ω^2,ω^4,ω^2

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Parikh, Kunal. "Simulation of Rectangular, Single-Layer, Coax-Fed Patch Antennas Using Agilent High Frequency Structure Simulator (HFSS)." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9663.

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The Range Limited Antenna (RLA) is a device, which accurately estimates the range of incoming signals and rejects those that arrive from outside a certain, pre-determined range. This task is accomplished by using two multi-element arrays and applying direction finding (DF) algorithms on each of them. Rectangular, single-layer, coax-fed patch antennas are used as array elements for the specific purpose of tracking cell phones operating in the PCS band inside a given building. It is vital to ensure that the patch antenna is designed in such a manner that it resonates at the desired frequency. This thesis introduces the Agilent High Frequency Structure Simulator (HFSS) as an effective tool for modeling electromagnetic structures. It presents a comprehensive and meticulous description of the process of modeling a rectangular coax-fed patch antenna in HFSS. Plots of S-parameter values are calculated and are compared with WIPL-D, which is another simulation software program, and with measurements performed at the George Washington University. Various important parameters of the HFSS simulation are varied and their effects are investigated to provide a deeper understanding of the program.
Master of Science

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Wegrzyk, Jennifer. "Wide-pulse, high-frequency electrical stimulation" in humans : Combined investigations of neural and muscular function using electrophysiological and nuclear magnetic resonance techniques." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4080.

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L'ectrostimulation dite conventionnelle (CONV) est délivrée par des impulsions électriques de basse fréquence (≤ 50 Hz), de courte durée (< 400 μs) et de haute intensité. Ce type d'ESNM permet ainsi d'évoquer une contraction musculaire grâce à l'activation directe des axones moteurs et est associé à une fatigue musculaire exagérée par rapport aux contractions volontaires (VOL). Au contraire, lors de l'utilisation d'impulsions de longues durées (1 ms), de hautes fréquences (≥ 80 Hz) et de faibles intensités (i.e. protocole « Wide-Pulse, High-Frequency » (WPHF)), une partie de la force musculaire évoquée aurait pour origine des mécanismes centraux. En effet, une augmentation de la force produite en réponse à WPHF a été rapportée alors que l'intensité de stimulation était constante. Cette « extra force » (EF) refléterait le recrutement par voie réflexe des motoneurones spinaux. L'objectif de ce travail de thèse était de mieux appréhender les mécanismes neurophysiologiques à l'origine de l'EF et d'évaluer les conséquences métaboliques et corticales du protocole WPHF (1 ms - 100 Hz) par rapport à des protocoles d'exercices VOL et de type CONV (50 μs - 25 Hz). Les réponses musculaires des fléchisseurs plantaires et les réponses cérébrales ont été évalué par résonance magnétique nucléaire (la spectroscopie par résonance magnétique du phosphore 31 du muscle et l'imagerie par résonance magnétique fonctionnelle du cerveau) et électrophysiologie (EMG). Ces résultats constituent une première étape importante vers une meilleure prise en charge des pathologies liées à des atteintes du neuromusculaire
Conventional neuromuscular electrical stimulation (CONV) is delivered via surface electrodes at short pulse duration (< 400 μs), low frequencies (≤ 50 Hz) and high current intensities. The motor unit recruitment pattern of CONV, however, is different from the pattern of voluntary contractions (VOL) and leads to a hastened onset of muscle fatigue. The use of wide-pulses (1ms), high frequencies (100 Hz) (WPHF) and low current intensities might approach the natural activation pattern of VOL by enhancing the neural contribution to force production. Previous studies investigating WPHF reported progressive and unexpected force increments ("Extra Forces") despite a constant stimulation intensity which might reflect the more pronounced activation of sensory pathways within the central nervous system. The objective of this thesis was to investigate this "Extra Force" (EF) phenomenon and to evaluate the efficiency of WPHF (1 ms pulse duration at 100 Hz) in terms of metabolic demand and neural contribution to force production in comparison to CONV NMES (0.05 ms pulse duration at 25 Hz) and VOL. Our experiments comprised electrophysiological (EMG) and nuclear magnetic resonance techniques (31P spectroscopy of the muscle, functional imaging of the brain). The findings should be considered in future studies investigating the potential of NMES in a clinical context as a treatment for neuromuscular pathologies

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Barrett, Anthony R. "Dynamic Testing of In-Situ Composite Floors and Evaluation of Vibration Serviceability Using the Finite Element Method." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28879.

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The presented research examined three areas: best practices in high quality dynamic testing of in-situ floor systems, extensive dynamic testing of three bare (non-fit out) in-situ multi-bay steel composite floors to estimate their dynamic parameters/response and to identify trends in dynamic behavior, and development of a set of fundamental finite element (FE) modeling techniques to adequately represent the dynamic response of steel composite floors for the purpose of evaluating vibration serviceability. The measurement, analysis, and computation of a floor's accelerance frequency response function (FRF) is the core premise linking all areas of the presented research. The burst chirp signal using an electrodynamic shaker is recommended as the most accurate and consistent source of excitation for acquiring high quality measurements suitable for use in parameter estimation, operating deflection shape animation, and calibration/validation of FE models. A reduced mid-bay testing scheme is recommended as a time-saving alternative to modal testing over a full coverage area, provided the only desired estimated parameters are frequencies, damping, and mid-bay acceleration response. Accelerance FRFs were measured with an electrodynamic shaker located within 23 unique bays on the three tested floors. Dominant frequencies ranged from 4.85 Hz to 9 Hz and measured estimates of damping varied considerably, ranging from 0.44% to 2.4% of critical (0.5%-1.15% was typical). Testing showed several mode shapes were localized to just a few bays and not all modes were adequately excited by forcing at a single location. The quality of the estimated mode shapes was significantly improved using multi-reference modal testing. FE models for the tested floors were developed based on high quality measured data and were shown to provide adequate representations of measured floor behavior. Fundamental techniques are presented for modeling mass, stiffness, boundary conditions, and performing dynamic analysis. A method of evaluating vibration serviceability was proposed using the FE model's computed accelerance FRF for comparison with a design accelerance curve that represents an acceleration response threshold in the frequency domain. An example design accelerance curve is presented based on current serviceability guidelines for acceleration tolerance and effective harmonic forces due to human activities such as walking.
Ph. D.

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50

Sefi, Sandy. "Computational electromagnetics : software development and high frequency modeling of surface currents on perfect conductors." Doctoral thesis, KTH, Numerisk Analys och Datalogi, NADA, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-590.

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In high frequency computational electromagnetics, rigorous numerical methods be come unrealistic tools due to computational demand increasing with the frequency. Instead approximations to the solutions of the Maxwell equations can be employed to evaluate th electromagnetic fields. In this thesis, we present the implementations of three high frequency approximat methods. The first two, namely the Geometrical Theory of Diffraction (GTD) and th Physical Optics (PO), are commonly used approximations. The third is a new invention that will be referred to as the Surface Current Extraction-Extrapolation (SCEE). Specifically, the GTD solver is a flexible and modular software package which use Non-Uniform Rational B-spline (NURBS) surfaces to model complex geometries. The PO solver is based on a triangular description of the surfaces and includes fas shadowing by ray tracing as well as contribution from edges to the scattered fields. GTD ray tracing was combined with the PO solver by a well thought-out software architecture Both implementations are now part of the GEMS software suite, the General ElectroMag netic Solvers, which incorporates state-of-the-art numerical methods. During validations both GTD and PO techniques turned out not to be accurate enough to meet the indus trial standards, thus creating the need for a new fast approximate method providing bette control of the approximations. In the SCEE approach, we construct high frequency approximate surface currents ex trapolated from rigourous Method of Moments (MoM) models at lower frequency. T do so, the low frequency currents are projected onto special basis vectors defined on th surface relative to the direction of the incident magnetic field. In such configuration, w observe that each component displays systematic spatial patterns evolving over frequenc in close correlation with the incident magnetic field, thus allowing us to formulate a fre quency model for each component. This new approach is fast, provides good control of th error and represents a platform for future development of high frequency approximations. As an application, we have used these tools to analyse the radar detectability of a new marine distress signaling device. The device, called "Rescue-Wing", works as an inflatabl radar reflector designed to provide a strong radar echo useful for detection and positionin during rescue operations of persons missing at sea.
QC 20101004

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Dissertations / Theses on the topic 'High frequency resonance method'

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