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1
Zimmer, Aline Katharina. "Investigation of the impact of turbine blade geometry on near-field microwave blade tip time of arrival measurements." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26558.
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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Jagoda, Jechiel; Committee Co-Chair: Jacobs, Laurence; Committee Member: Seitzman, Jerry. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Folgar, Carlos Eduardo. "Structure Evolution of Silica Aerogel under a Microwave Field." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27801.
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Structure evolution of silica aerogel was studied in microwave- and conventionally processed samples over the temperature range from 25 to 1200â °C. The samples were produced using sol-gel processing and dried under carbon dioxide supercritical conditions. After drying, the monolithic samples received a thermal treatment at different programmed temperatures in two different ovens, conventional and microwave. The microwave process was performed using a single mode microwave oven at 2.45GHz. Dielectric properties were measured using the cavity perturbation method, and structural characterization was carried out using a variety of techniques, including absorption surface analysis, Helium pycnometry, Archimedes principle, Fourier transform infrared spectroscopy, X-ray diffraction, and high resolution microscopy. The data obtained revealed that structural differences do exist between microwave- and conventionally processed samples.
Three different regions were identified from the structural characterization of the samples. Regions I exhibited a structure densification at temperatures between 25 and 850â °C. Region II was characterized by a bulk densification in the temperature range from 850 to 1200â °C. Region III was represented by the onset of crystallization above 1200â °C. Explanation and possible causes behind the structural differences observed in each region are provided. In general, the structure evolution observed in microwave- and conventionally processed samples followed the same order, but occurred at lower temperature for the microwave process.Ph. D.
3
Narayana, Merugu Lakshmi. "Concurrent algorithms for microwave and millimetre wave field problems." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334591.
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Rossek, Sacha J. "Direct optical control of a microwave phase shifter using GaAs field-effect transistors." Thesis, Middlesex University, 1995. http://eprints.mdx.ac.uk/10682/.
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The design and analysis of a novel optical-to-microwave transducer based upon direct optical control of microwave gallium arsenide (GaAs) field-effect transistor (FET) switches is the subject of this thesis. The switch is activated by illuminating the gate depletion region of the FET device with laser light having a photon energy and wavelength appropriate to the generation of free carriers (electron-hole pairs) within GaAs. The effects of light on the DC and microwave properties of the GaAs FET are explored and analyzed to permit the characterization of the switching performance and transient response of a reflective microwave switch. The switch is novel in that it utilizes direct optical control, whereby the optically controlled GaAs FET is directly in the path of the microwave signal and therefore relies on optically-induced variations in the microwave characteristics of the switch. This contrasts with previous forms of optically controlled switches which rely on indirect methods with the optical stimulus inducing variations in the DC characteristics of the GaAs FET, such that there is no direct interaction between the optically illuminated GaAs FET and the microwave signal. Measured and simulated results relating to the switching performance and transient response of the direct optically controlled microwave switch have been obtained and published as a result of this work. For the first time, good agreement is achieved between the measured and simulated results for the rise and fall times associated with the transient response of the gate photovoltaic effect in optically controlled GaAs FET switches. This confirms that the GaAs FET, when used as an optically controlled microwave switch, has a transient response of the order of several micro-seconds. An enhanced model of the GaAs FET switch has been developed, which represents a more versatile approach and leads to improved accuracy in predicting switching performance. This approach has been shown to be valid for both optical and electrical control of the GaAs FET. This approach can be used to model GaAs FET switches in discrete or packaged forms and predicts accurately the occurrence of resonances which may degrade the switch performance in both switching states. A novel method for tuning these resonances out of the switch operating band has been developed and published. This allows the switch to be configured to operate over the frequency range 1 to 20 GRz. The agreement between the models and measured data has been shown to hold for two very different GaAs FET structures. The results of the direct optically controlled microwave GaAs FET switch have been used as the basis for the design of a novel direct optically controlled microwave phase shifter circuit; Measured and simulated results are in good agreement and verify that the performance of the optically controlled phase shifter is comparable with previously published results for electrically controlled versions of the phase shifter. The 10 GRz phase shifter was optically controlled over a 1 GRz frequency range and exhibited a mid-band insertion loss of 0.15 dB. The outcome of the work provides the basis for directly controlling the phase of a microwave signal using the output of an optical sensor, with the GaAs FET acting as an optical-to-microwave transducer through a monolithic interface.
5
Barkhordarian, V. "The design and fabrication of Microwave Field-Effect Transistors." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233220.
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Saleh, Wael Mouin. "Non-invasive near-field microwave detection of breast cancer." Thesis, University of Exeter, 2007. http://hdl.handle.net/10036/32212.
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The spread of breast cancer worldwide and the need for new technologies to improve breast cancer detection present a challenge to the standard medical screening methods. Tumour detection, in the early stages, is crucial if patients are to be treated effectively and with minimally invasive procedures. Thus, any technique that can improve on, or add to, existing breast tumour detection methods is welcome. In this thesis just such a technique based on near-field microwave imaging is investigated, both theoretically and experimentally. The electromagnetic waves interaction with dielectric structure is fundamental for any microwave application. Thus it is essential to understand the interaction of the microwaves radiated from the sensor (open-ended rectangular waveguide) with the breast structure under investigation. A detailed mathematical model describing the interaction of microwaves emitted from an open rectangular wave-guide with an N-layer dielectric structure is developed, using the Fourier Transform Matching method. The model is capable of calculating the electric field properties anywhere within the N-layer structure, as well as the complex reflection coefficient existing at the waveguide aperture. Computer simulations, based on the mathematical formulations derived using the Fourier Transform Matching method, of the near-field radiation patterns in a 3-layer approximation to the general N-layer model are presented. Such simulations are most useful in assessing the suitability of near-field microwave non-invasive testing and evaluation (NIT&E) technique for breast tumour detection. In addition, simulated 1-D and 2-D reflection phase and magnitude images are calculated and presented for the 3-layer structure with an inclusion to represent the presence of a tumour. Parameters controlling the detection sensitivity, specifically the frequency of operation, waveguide filling, and standoff distance dielectric filling, are investigated to obtain the optimal - 2 - parameters for the inspection system. The theoretical simulations show that a high sensitivity in both reflection coefficient magnitude and phase should be obtainable. Experimental measurements of the reflection coefficient magnitude and phase when imaging a breast phantom that imitates real breast dielectric properties contrast are also presented. The phantom comprises a plexiglass container filled with soybean oil to represent normal breast tissue, with a small balloon filled with diacetin solution to represent the tumour. Both uncalibrated and calibrated measurements of reflection coefficient magnitude and phase were performed. The microwave source comprised an open-ended rectangular waveguide operating in the frequency range of approximately 8.2 to 12.4 GHz. Calibrated measurements were performed using a slotted waveguide system. An in-depth analysis between calibrated measurements and simulation results for a simple dielectric structure is illustrated to verify the simulation results. Then, calibrated measurements for breast phantom are obtained. Finally, a theoretical-versus-experimental qualitative assessment for the breast phantom verifies the mathematical model developed in the thesis. Thus, a near-field microwave non-invasive detection prototype is designed to experimentally detect tumour presence via measuring the sensor’s aperture reflection coefficient.
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Mirkhaydarov, Bobur. "InAs nanowire field-effect transistors as RF/microwave switches." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/845099/.
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This project was dedicated to the development of solution-processed nanomaterials-based high-performance field-effect transistors (FETs) suitable for a new application area of printed reconfigurable antennas. The focus of research was on implementing solution processed high electron mobility InAs nanowires (NWs) as semiconducting channel in field effect transistors. The key direction of this work was the development of InAs NWs FETs with a designated high frequency waveguide geometry to enable they operation as microwave switch elements. Initially, InAs NW FETs were developed and tested in direct – current mode to allow evaluation and extraction of key transistor performance parameters such charge carrier mobility, threshold, on/off ratio, transconductance, subthreshold swing, and on-channel resistance. The InAs NW were assembled from nanowire ‘inks’ in the FETs channel via electric -field assisted assembly technique, dielectrophoresis. Nanowires were directly incorporated in FETs with bottom-gate architecture on Si/SiO2 substrates, and with top-gate architecture on quartz substrates with polymeric gate dielectrics. Current-voltage characteristics were measured both in controlled dry nitrogen atmosphere and ambient environment, and demonstrated an instability of unprotected InAs NW in ambient air. Protection of nanowire channel with Al2O3 layers has resulted in significant improvement of device stability. Optimised InAs NW FET devices demonstrated electron mobility over 1000 cm2/Vs and on-off current ratios up to 1000. Finally, a proof of principle for solution processed InAs NW field-effect transistors operating as microwave switches in 5-33GHz frequency range have been demonstrated. FET devices were implemented in co-planar waveguide (CPW) microwave transmission line geometry, providing efficient transmission or reflection of microwave signal. The FETs demonstrated high performance with transistor ON-state resistance as small as ≈50 Ω providing an excellent impedance match to that of microwave waveguide. Bringing FETs to the OFF state provided 1000 times resistance increase, resulting in FET microwave switch behaviour, characterised by ~10 dB change in scattering (S)-parameters, such as difference in transmission coefficient S21 between on/off switching states.
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Hamilton, Clive A. "Effects of magnetic and microwave fields on chemical reactions." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236269.
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Królak, Radoslaw [Verfasser]. "Investigation of field suitable microwave cavity measurement approaches / Radoslaw Królak." Aachen : Shaker, 2017. http://d-nb.info/1138177067/34.
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Zhou, Qiping. "Near-field microwave imaging with coherent and interferometric reconstruction methods." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1591903415194694.
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Terril, Nathaniel D. "Field Simulation for the Microwave Heating of Thin Ceramic Fibers." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36863.
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Microwave processing of ceramics has seen a growth in research and development efforts throughout the past decade. One area of interest is the exploration of improved heating control through experiments and numerical modeling. Controlled heating may be used to counteract non-uniform heating and avoid destructive phenomena such as cracking and thermal runaway. Thermal runaway is a potential problem in materials with temperature dependent dielectric properties. As the material absorbs electromagnetic energy, the temperature increases as does its ability to absorb more energy. Controlled processing of the material may be achieved by manipulating the applied field. The purpose of this research is to model the interaction of the EM-field with a thin ceramic fiber to investigate possible mechanisms that may affect the heating process. The fiber undergoes microwave heating in a single-mode resonant applicator. Maxwell's equations for the fields within the cavity are solved using mode-matching techniques taking into account the field interaction of the fiber and an arbitrarily shaped coupling aperture. Effects of varying the aperture shape on the field distribution are explored. The coupled nature of the electromagnetic solution with the material's temperature-dependent properties, including an analysis of non-uniform heating, is also discussed.Master of Science
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Harty, Thomas P. "High-fidelity microwave-driven quantum logic in intermediate-field 43Ca+." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:55264c2d-bb42-4439-bf49-731b9f66de74.
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This thesis is concerned with the development of an intermediate magnetic field "clock-qubit" in 43Ca+ at 146G and techniques to manipulate this qubit using microwaves and lasers. While 43Ca+ has previously been used as a qubit, its relatively complicated level structure - with a nuclear spin of 7/2 and low-lying D-states -- makes cooling it in the intermediate field an intimidating prospect. As a result, previous experiments have used small magnetic fields of a few gauss where coherence times are limited and off-resonant excitation is a significant source of experimental error. We demonstrate a simple scheme that allows 43Ca+ to be cooled in the intermediate field without any additional experimental complexity compared with low fields. Using the clock-qubit, we achieve a coherence time of T*2 = 50 (10)s - the longest demonstrated in any single qubit. We also demonstrate a combined state preparation and measurement error of 6.8(6)x 10-4 - the lowest achieved for a hyperfine trapped ion qubit [NVG+13] - and single-qubit logic gates with average errors of 1.0(3) x 10-6 - more than an order of magnitude better than the previous record [BWC+11]. These results represent the state-of-the-art in the field of single-qubit control. Moreover, we achieve them all in a single scalable room-temperature ion trap using experimentally robust techniques and without relying on the use of narrow-linewidth lasers, magnetic field screening or dynamical decoupling techniques. We also present work on a recent scheme [OWC+11] to drive two-qubit gates using microwaves. We have constructed an ion trap with integrated microwave circuitry to perform these gates. Using this trap, we have driven motional sideband transitions, demonstrating the spin-motion coupling that underlies the two-qubit gate. We present an analysis of likely sources of experimental error during a future two-qubit gate and the design and preliminary characterisation of apparatus to minimise the main error contributions. Using this apparatus, we hope to perform a two-qubit gate in the near future.
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Balaji, Uma. "Field theory analysis and design of circular waveguide components." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32732.pdf.
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Bayat, Nozhan. "On the role of antennas in the achievable resolution and accuracy from near-field microwave tomography." Progress In Electromagnetics Research, 2013. http://hdl.handle.net/1993/23906.
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This thesis studies the role of antennas in the achievable resolution and accuracy from nearfield
microwave tomography (MWT). Near-field MWT is an emerging imaging modality in
which the object being imaged is successively irradiated by several antennas, located close
to the object, in the microwave frequency range. The scattered fields emanating from the
object are then processed to form quantitative images from the dielectric properties of the
object.
This thesis starts with proposing a mathematical framework to study the achievable resolution
from MWT. Within this framework, the effect of the near-field distribution of the
utilized antennas on the achievable image resolution will be studied. Specifically, it will be
shown that the use a focused near-field distribution to irradiate the object can enhance the
achievable resolution. Within the same framework, the effects of the frequency of operation,
multiple frequencies of operation, signal-to-noise ratio of the measured data, and the number
of antenna elements on the achievable resolution and accuracy will be studied.
After establishing the importance of the antenna’s incident field distribution, this thesis continues
with investigating two different methods to achieve a focused near-field distribution.
The first method, which attempts to synthesize focused beams from existing omnidirectional
antenna elements, will be shown to be not successful using the method employed in this thesis.
The second method is based on modifying an existing antenna element so as to make its
near-field distribution more focused. Through different experiments and simulations, it will
be shown that the second method can make the near-field distribution of the antenna more
focused while maintaining multiple frequencies of operation for the antenna, and keeping its
physical size reasonably small.
15
Chen, Qiang. "Finite-difference time-domain method for combined large signal circuit and electromagnetic field analysis." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337664.
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Ren, Kai. "Physics-Based Near-Field Microwave Imaging Algorithms for Dense Layered Media." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1511273574098455.
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Cordoba, Erazo Maria Fernanda. "Near-field Microwave Microscopy for Surface and Subsurface Characterization of Materials." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5930.
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This dissertation presents an investigation on the capabilities of Near-Field Microwave Microscopy (NFMM) for the characterization of surface and subsurface materials. Subsurface characterization refers to the detection, differentiation and imaging of dielectric, and metallic features that are coated with an insulating layer. The design, simulation and modeling, and testing of a dielectric resonator (DR)-based NFMM and a coaxial transmission line resonator-based NFMM are discussed in detail in this work. Additionally, materials differentiation and imaging capabilities of each microscope are examined using several bulk samples, liquids, GaAs MMIC circuits, and gold/glass testing patterns.
The 5.7 GHz DR-based NFMM uses a microwave probe that consists of a commercial gold-coated probe tip coupled to a DR through a non-resonant microstrip line. The probe is enclosed in an aluminum cavity to preserve the quality factor of the probe (Q=986) and therefore to enhance its sensitivity. The development of a lumped-element model of this DR-based probe is discussed in this work. Characteristics of this design are its high Q and the ability to resolve differences in permittivity (E’r) of insulting bulk samples and liquids as small as ∆E’r =1.75 and ∆E’r =0.04, respectively. The imaging capabilities of this design were verified using a GaAs MMIC phase shifter. It was found that a 10 um wide microstrip line is successfully resolved and that the spatial resolution of the microscope is 50 um when using a tungsten tip with an apex radius of 25 um. Additionally, measurement of the electrical resistance of an additive manufactured resistor was measured using the DR-based NFMM without the need of contacts. The percent difference between the electrical resistance measured using the DR-based NFMM and a four-point probe is 9.6%. Furthermore, the DR-based NFMM allows simultaneous imaging of topography and RF electrical conductivity of rough thick films without the need of an additional distance sensor; this ability is demonstrated for a rough CB028 thick film.
The 5GHz coaxial resonator transmission line-based NFMM employs a half-wavelength coaxial transmission line resonator terminated in a sharp tungsten tip as the microwave probe. A quartz-tuning fork based distance following feedback system is integrated with the microwave probe in order for the NFMM to operate in non-contact mode. The Q of the probe is degraded by 30% (Q=55) due to the presence of the quartz tuning fork. Despite the low Q, this NFMM is able to differentiate several insulating bulk samples (3.8 < E’r < 25) even if they are coated with an insulating layer of thickness similar to the apex radius of the tungsten tip. Finally, the coaxial resonator transmission line-based NFMM is able to image subsurface permittivity distribution of a flexible polymer-composite PDMS-Ba0.55Sr0.45TiO3 49% which is coated with 10 um thick parylene-C layer. Measurements performed at a tip-sample distance of 100 nm reveal that within an area of 50 um x 50 um, the relative permittivity of the polymer-composite is not constant but varies between 6.63 and 11.78.
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Darling, Robert Bruce. "A theory for optically-gated gallium-arsenide MESFETS." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/15668.
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Shivhare, Uma Shanker. "Drying characteristics of corn in a microwave field with a surface-wave applicator." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70344.
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Microwave drying of corn was investigated at selected levels of initial moisture content, absorbed power by grain, and temperature and superficial velocity of air at inlet. A surface-wave applicator was used to couple microwaves with the corn.The drying rate curves indicated that the microwave drying of corn took place in the falling rate period. It was hypothesized that diffusion is the controlling mechanism for moisture transfer from within the kernel in microwave drying of corn.
A mathematical model was developed to describe the change in moisture content at the surface as a function of the free moisture content of corn. The diffusion model employing varying surface conditions was used to describe the microwave drying process. An Arrhenius type equation was developed to describe the relationship between the diffusion coefficient and the outlet air temperature. The diffusion coefficient values varied from 0.0008 to 0.0082 cm$ sp2$/h when constant levels of microwave power were applied continuously for drying corn. Equilibrium moisture content was determined and regression equations were developed to describe the EMC with microwave power and air velocity.
The diffusion coefficient increased with the levels of absorbed power, decreased with increasing air velocity but remained insensitive to the inlet air temperature when microwaves were applied continuously for drying corn. The increased drying rates at higher power levels reduced the drying time considerably but at the cost of energy loss through the passing air and reduced germination and bulk density of dried corn. Application of absorbed microwave power at 0.25 W/g resulted in greater than 92% germination of dried corn. Deleterious effects on product quality was observed when the applied power exceeded 0.75 W/g.
Pulsed and variable microwave power effects were investigated in order to optimize the drying process. Time for drying corn increased but the effective duration for which microwaves were applied and the energy requirement in the pulsed mode was lower compared to both continuous and variable microwave operation.
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Tantong, Somsak. "Near field microwave imaging techniques for embedded object detection and shape reconstruction." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4952.
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Thesis (M.S.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on January 11, 2008) Includes bibliographical references.
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Janice, Brian A. "Differential Near Field Holography for Small Antenna Arrays." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/999.
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"Near-field diagnosis of antenna arrays is often done using microwave holography; however, the technique of near-field to near-field back-propagation quickly loses its accuracy with measurements taken farther than one wavelength from the aperture. The loss of accuracy is partially due to windowing, but may also be attributed to the decay of evanescent modes responsible for the fine distribution of the fields close to the array. In an effort to achieve better resolution, the difference between these two phase-synchronized near-field measurements is used and propagated back. The performance of such a method is established for different conditions; the extension of this technique to the calibration of small antenna arrays is also discussed. The method is based on the idea of differential backpropagation using the measured/simulated/analytical data in the near field. After completing the corresponding literature search authors have found that the same idea was first proposed by P. L. Ransom and R. Mittra in 1971, at that point with the Univ. of Illinois. This method is basically the same, but it includes a few distinct features: 1. The near field of a (faulty) array under test is measured at via a near field antenna range. 2. The template (non-faulty) near field of an array is simulated numerically (full-wave FDTD solver or FEM Ansoft/ANSYS HFSS solver) at the same distance - an alternative is to use measurements for a non-faulty array. 3. Both fields are assumed (or made) to be coherent (synchronized in phase). 4. A difference between two fields is formed and is then propagated back to array surface using the angular spectrum method (inverse Fourier propagator). The corresponding result is the surface (aperture) error field. This approach is more precise than the inverse Rayleigh formula used in Ransom and Mittra's paper since the evanescent spectrum may be included into consideration. 5. The error field magnitude peaks at faulty elements (both amplitude and phase excitation fault). 6. The method inherently includes all mutual coupling effects since both the template field and the measured field are full-wave results."
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Craik, Diana Prado Lopes Aude. "Near-field microwave addressing of trapped-ion qubits for scalable quantum computation." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:7ca0a411-a12f-41d3-ab2b-09025388c462.
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This thesis reports high-fidelity near-field spatial microwave addressing of long-lived 43Ca+ "atomic clock" qubits performed in a two-zone single-layer surface-electrode ion trap. Addressing is implemented by using two of the trap's integrated microwave electrodes, one in each zone, to drive single-qubit rotations in the zone we choose to address whilst interferometrically cancelling the microwave field at the neighbour (non-addressed) zone. Using this field-nulling scheme, we measure a Rabi frequency ratio between addressed and non-addressed zones of up to 1400, from which we calculate an addressing error (or a spin-flip probability on the qubit transition) of 1e-6. Off-resonant excitation out of the qubit state is a more significant source of error in this experiment, but we also demonstrate polarisation control of the microwave field at an error level of 2e-5, which, if combined with individual-ion addressing, would be sufficient to suppress off-resonant excitation errors to the 1e-9 level. Further, this thesis presents preliminary results obtained with a micron-scale coupled-microstrip differential antenna probe that can be scanned over an ion-trap chip to map microwave magnetic near fields. The probe is designed to enable the measurement of fields at tens of microns above electrode surfaces and to act as an effective characterisation tool, speeding up design-fabrication-characterisation cycles in the production of new prototype microwave ion-trap chips. Finally, a new multi-layer design for an ion-trap chip which displays, in simulations, a 100-fold improvement in addressing performance, is presented. The chip electrode structure is designed to use the cancelling effect of microwave return currents to produce Rabi frequency ratios of order 1000 between trap zones using a single microwave electrode (i.e. without the need for nulling fields). If realised, this chip could be used to drive individually addressed single-qubit operations on arrays of memory qubits in parallel and with high fidelity.
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Murgia, David. "Microchip ion traps with high magnetic field gradients for microwave quantum logic." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48045.
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This thesis describes experimental work towards the development of a trapped-ion quantum computer based on microchip ion traps and long-wavelength radiation, using magnetic field gradients. The relationship between experimental parameters and two-qubit gate fidelity is investigated for microchips with two different static magnetic field gradient generation methods. For current-carrying wires and under-chip permanent magnets, optimum ion heights of 110 μm and 200 μm are found respectively. Construction of an experiment capable of demonstrating high-fidelity gates is reported, including innovations for the use of microchip ion traps with permanent magnets. The development of a vacuum system for versatile microchip experiments is described, including new methods for impedance-matched RF delivery, in-vacuum filtering and liquid nitrogen microchip cooling. Protection of both the microchip surface from atomic flux and of ions from the charged imaging viewport are both investigated in detail. A new preparation framework for microchip ion traps before their use in experiments is developed. In order to remove unwanted deposited layers on the microchips, a process of multiple chemical treatments is used. In addition, these characterisation efforts lead to refinement of the microfabrication process for future microchips. The application of large currents to microchips is of fundamental importance to scalable trapped-ion quantum computing using static magnetic field gradients. As part of the characterisation process, currents of ≈ 10A are successfully applied to microfabricated current-carrying wires, demonstrating the viability of these structures for generation of local magnetic fields and gradients in a quantum computing device. The operation of a microchip ion trap experiment with under-chip permanent magnets for a high magnetic field gradient (≈ 140Tm−1) is described. The successful trapping of ytterbium-174 and -171 ions is reported, as well as their use to measure and optimise the ion trap parameters. The thesis concludes with consideration of the expected future results from the ongoing operation of the experiment.
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Gu, Sijia. "Contribution to broadband local characterization of materials by near-field microwave microscopy." Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10175/document.
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Les microscopes champ proche micro-ondes sont des instruments émergents pour la caractérisation de matériaux. Dans ce travail, un microscope champ proche micro-ondes fait maison est d'abord décrit et analysé en termes de résolution et de largeur de bande de fréquences de fonctionnement. Ensuite, il est mis en œuvre pour la caractérisation d'une grande variété de matériaux tels que par exemple des métaux, des semi-conducteurs, des diélectriques, des liquides et des nanomatériaux 2D. Le système intégre un interférométre pour améliorer la sensibilité de la mesure pour des fréquences de fonctionnement couvrant la bande 2-18 GHz. La sensibilité et les différents modes de fonctionnement disponibles (contact, sans contact, environnement liquide) permettent d'adresser une grande variété de domaines d'applications. La résolution latérale obtenue par cet instrument est plus petite de plusieurs ordres de grandeur que la longueur d'onde de fonctionnement, ouvrant ainsi la voie à une caractérisation locale. Les propriétés électromagnétiques des matériaux ont été extraites en utilisant la méthode de perturbation et celle de la ligne de transmission. En particulier, les propriétés diélectriques de solutions salines aqueuses et l’impédance complexe du graphène ont été étudiées dans une large bande de fréquence. Ce microscope champ proche micro-ondes basé sur une méthode interférométrique qui permet une analyse quantitative des propriétés des matériaux de manière non-destructive peut adresser un grand éventail d’applications dans de nombreux domaines scientifiques. Enfin, l’ensemble des résultats montre que potentiellement la microscopie champ proche micro-ondes dispose des atouts pour devenir un outil de métrologie important pour la caractérisation en micro- et nano-électroniqueNear-field microwave microscopes are emerging instruments for materials characterization. In this work, a home-made near-field microwave microscope is first described and analyzed in terms of resolution performance and frequency band of operation. Then, it is applied to the characterization of a large variety of materials such as metals, semiconductors, dielectrics, liquids and 2D nanomaterials. The system is based on an interferometric technique to improve the measurement sensitivity in the entire frequency range of operation spanning from 2 to 18 GHz. The sensitivity and the different operating modes available (contact, non-contact, liquid environment) allow addressing a large variety of application fields. The instrument allows a sub-wavelength lateral resolution which is more than two orders of magnitude smaller than the operating wavelength, opening the way to a local characterization. The cavity perturbation and transmission line approaches have been used to extract the electromagnetic properties of materials. In particular dielectric properties of saline aqueous solutions and complex impedance of graphene have been investigated in a broad frequency band. It provides a quantitative analysis of material properties in a non-destructive manner to address numerous applications in many scientific fields. Finally, all the results together show that the interferometer-based near-field microwave microscope has the potential to become an important metrology tool for characterizations in micro- and nano-electronics
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Kahle, A. "Cosmic microwave background anisotropies in the presence of a weak magnetic field." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/4894.
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Bibliography: leaves 87-90.One of the questions cosmology still has not satisfactorily resolved is the origin of magnetic fields in the universe. These have been observed at all scales where man has c:evised means to observe them, from stellar scales, to intergalactic and intercluster scales. Indeed, there is no reason to believe that they are not present, at some level, at even larger scales. However, a satisfactory explanation for their origin is yet to be found. The two most popular theories for the creation of these magnetic fields, namely the Galactic dynamo, and primordial field amplification, both rely on the presence of a seed field, which they then amplify. However, the galactic dynamo requires a far weaker seed field compared to primordial field amplification. It would thus be helpful, in trying to understand magnetogenesis, if one could discover some means to detect such a seed field. One way to do so would be to search for a signature that such a magnetic field might leave on the CMB, and then look for the presence of this signature in CMB observations. This is the principal aim of this thesis.
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Wang, Yanmin. "Field-dependent impedance, rectification and microwave transmission in poly(3,4-ethylenedioxythiophene) nanocomposites." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427240.
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Lin, Tianjun. "Investigation of microwave imaging and local dielectric characterization of materials by using a homemade interferometer-based near-field microwave microscope." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I016/document.
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La microscopie champ proche micro-onde, qui fait partie de la famille des microscopies à sonde locale, est envisagée aujourd’hui dans de nombreux domaines d’applications de la physique, de la biologie et des micro et nanotechnologies. Dans ce manuscrit, le microscope micro-onde à champ proche qui est exploité est un instrument développé au laboratoire IEMN bénéficiant d’une grande sensibilité dans une large bande de fréquences de travail [2-18 GHz]. Le potentiel d’applications du microscope est démontré au travers de la caractérisation de liquides avec différentes modalités de caractérisation (sonde en contact, sans contact et en immersion). En particulier, cet outil est mis en œuvre pour la spectroscopie diélectrique de solutions aqueuses de glucose.Cet instrument qui offre une capacité d'imagerie sub-longueur d'onde est également testé pour différentes situations (imagerie de surface et de sub-surface). La résolution d'imagerie ainsi que la précision de mesure sont évaluées puis des méthodes de traitement d'images simples sont proposées pour améliorer la qualité de l'imagerie. Enfin, une piste pour une intégration plus grande de l’instrument, qui consisterait à remplacer l’analyseur de réseau par un dispositif plus compact (type réflectomètre six-ports) est exploréeNear-field microwave microscopes, which belong to the local scanning probe microscopes family, are considered today as advanced characterization tools in many applications areas including physics, biology and micro and nanotechnologies. The near-field microwave microscope that is used in the work and described in this manuscript is an instrument developed at IEMN owning a great sensitivity in a wide operating frequency band [2-18 GHz]. The potential of the microscope in terms of applications is demonstrated through the characterization of liquids with different modalities of characterization (probe in contact, non-contact and immersed in a liquid). In particular, this instrument is investigated for dielectric spectroscopy of aqueous glucose solutions.This characterization tool that offers sub-wavelength imaging capability is also tested in different situations (surface and subsurface imaging). Imaging resolution and measurement accuracy are evaluated and easily implementable processing methods are proposed to improve the quality of imaging. Finally, a solution towards a larger compactness of the instrument is investigated through the replacement of the network analyzer by a more compact device (six-port reflectometer type)
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Tenorio-Pearl, Jaime Oscar. "Coherent control of a trapped electron in a disordered dielectric." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708428.
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McConnell, Brian Gregory. "A Coupled Heat Transfer and Electromagnetic Model for Simulating Microwave Heating of Thin Dielectric Materials in a Resonant Cavity." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/36179.
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Microwave heating is an emerging but still underutilized tool in modern industrial applications. The task of designing microwave applicators for heating industrial materials with temperature-dependent properties is challenging, and trial-and-error system prototyping is an expensive and wasteful means to accomplish this goal. The purpose of this work is to combine existing heat transfer and electromagnetic models to provide a complete simulation for heating dielectric materials in a resonant microwave cavity. The numerical simulation is validated by comparison to several independent sets of experimental data. The ultimate goal is to provide a research tool that will facilitate the industrial microwave applicator design process. With a complete, accurate, and user-friendly numerical simulation, parameters affecting the temperature distribution in stationary and moving process materials can be studied to optimize the results before the first prototype is made. This work also explores the sources of power loss in a microwave system and develops means for quantifying these power losses.Master of Science
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Rinkevich, A. B., M. I. Samoylovich, and A. F. Belyanin. "Effective Conductivity and Magnetic Permeability of Nanostructured Materials in Magnetic Field." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35340.
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The problem of homogenization the nanostructured materials placed in DC magnetic field has been discussed. The experimental data are obtained using metallic superlattices, metal-dielectric thin films and 3D-nanostructured materials. All these materials contain ferro- or ferrimagnetic component. The trans-mission and reflection coefficients were measured on the waves of millimeter waveband. It has been shown that the experimental frequency spectra of the coefficients in zero magnetic field can be described by the effective conductivity and dielectric permittivity. The spectra of ferromagnetic resonance, however, cannot be calculated correctly with the averaged magnetization.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35340
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Himadri, Pandey. "Fabrication, Characterization and Simulation of Graphene Field Effect Transistors operating at Microwave Frequencies." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129401.
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With the end of Si based Metal Oxide Semiconductor Field Effect Transistor scaling paradigm approaching fast as predicted by the Moore’s Law, and the technological advancements as well as human needs in many ways pushing for faster devices, graphene has emerged as a powerful alternative solution. This is so because of its very special properties like high charge carrier mobility, highly linear dispersion relation, high current carrying capacity and so on. However, since we have a finite resistance at Dirac point, the on/off ratio in graphene devices is sufficiently low, making graphene devices not so suitable for logical applications. At the same time, the 1/f noise, which is understood till now to originate from surface disorders like those observed in a two-dimensional electron gas system like graphene and is a major unwanted outcome in mesoscopic regime devices, reduces very much at high frequencies, making these devices good candidates for high frequency analogue applications. Motivated by these observations, this work explores fabrication and characterization of graphene field effect transistors operating at microwave frequencies, and compares a double gated device performance to a mono-gated device having the same geometry, dielectric layer thickness and gate length. A simple electrostatic finite element simulation model has also been developed to support our experimental observations by fitting simulated gate coupling capacitance values to the measured data. The model helps us in understanding the level of interface trap charge densities introduced into the device channel during fabrication, and the effect of quantum capacitance on device performance, and is in line with the experimental observations. Our results show that a double gated graphene FET has superior performance compared to a mono-gated FET.
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Takahashi, Susumu. "Angle-dependent high magnetic field microwave spectroscopy of low dimensional conductors and superconductors." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012927.
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Duchez, Wilfried. "Role of electric field profiles in continuous microwave processing of thermal runaway materials." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02132009-171150/.
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Kojima, Seishiro. "Novel Beamforming and Antenna Techniques for Microwave Power Transmission in Radiating Near Field." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263667.
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Francis, Caroline. "The local galaxy density field and its effects on the cosmic microwave background." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/28057.
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This thesis presents a reconstruction of the local galaxy density field to zmax = 0.3 from a photometric galaxy catalogue based on the Two Micro All-Sky Survey (2MASS) Extended Source Catalogue (XSC). A Wiener filter approach is adopted for the reconstruction, which is carried out using a basis of spherical harmonics to describe angular variations and spherical Bessel functions to describe the radial part of the field. The angular resolution is fixed with lmax = 30 (Δθ ~ 6°) and the radial resolution is set to match this at the characteristic redshift of the survey, z ~ 0.1, resulting in Δr ~ 30 h-1Mpc. A novel technique for replacing missing information from the galactic plane is developed and tested using simulation data. This reconstruction is used to predict the contribution to the Cosmic Microwave Background (CMB) of the local Integrated Sachs-Wolfe (ISW) effect and large-scale thermal Sunyaev-Zel’dovich (tSZ) effect. The impact of the predicted local ISW effect on the observed CMB signal is investigated, particularly with regard to reported anomalies on large angular scales. It is found that this local ISW signal to zmax = 0.3 can alleviate these anomalies by altering the amplitudes and positions of significant temperature extrema.
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Gebara, Edward. "Cryogenic on-wafer microwave load-pull power measurements and device performance analysis." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19601.
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Magill, Brenden A. "Microwave spectroscopy of edge and bulk modes of two dimensional electrons in magnetic field." Thesis, The Florida State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3564920.
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Edge magnetoplasmons (EMPs) and pinning mode resonances in two dimensional electron systems (2DESs) can both be thought of as lower hybrid modes of cyclotron and plasma resonances. This dissertation describes low temperature microwave spectroscopy of both of these modes. EMPs have oscillating charge confined at the 2DES edge by the combination of the perpendicular magnetic field and the electrostatic potential that produces the edge. Pinning mode resonances are from electron solids oscillating against confinement provided by disorder in the bulk of the 2DES.
The first part of this dissertation concerns the search for a mode similar to an EMP but confined solely by a linear magnetic inhomogeneity in the perpendicular magnetic field (Bz). While we do not observe such an excitation, we do observe a marked reduction in the velocity of an EMP in the presence of a Bz-inhomogeneity.
In the second part of this dissertation, we investigate pinning modes in “wide'' quantum well samples, for which the effective electron-electron interaction is softened at short range due to the vertical extent of the wavefunction. We observe a pinning mode resonance whose peak frequency (fpk ) vs Landau level filling (ν) shows an anomalous increase as ν moves away from ν = 1 under roughly the same conditions as anomalous quantum Hall effects observed previously in DC transport. A region of ν with enhanced fpk is interpreted as evidence for a new electron solid phase.
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Harscher, Peter. "Field simulator based optimization and automated tuning techniques for microwave and millimeter-wave filters /." [S.l.] : [s.n.], 2003. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15199.
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Zhang, Rong. "Preparation, electroactive properties and field controlled microwave transmission of polythiophene based conducting polymer composites." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398610.
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Schlegel, Jennifer Lynn. "Imaging the spatial variation of dielectric constant in materials using microwave near field microscopy." Available to US Hopkins community, 2003. http://wwwlib.umi.com/dissertations/dlnow/3080759.
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Fan, Hongmei. "Correlation between near field and far field radiated emission of printed circuit boards by genetic algorithms." Western Australian Telecommunications Research Institute, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0129.
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Most electromagnetic interference standards specify that measurements of radiated emissions must be performed in the far field (FF), e.g. at an open-area test site or in a semi-anechoic chamber. Since near field (NF) measurements are cheaper, quicker and more flexible compared to FF tests, establishing a correlation between NF and FF data is of great research interest. One strategy to achieve this goal is to find a set of basic radiators comprising electric and magnetic dipoles that generate the same NF as the original source at selected observation points. This set of dipoles, based on the uniqueness theorem, can then be used to predict the FF radiation patterns. The uniqueness theorem requires that electric or magnetic fields are matched on a closed surface with respect to the magnitude and phase. The focus of this thesis is the investigation of FF prediction based on NF magnitude-only data. In this thesis, a robust NF-FF conversion model based on Genetic Algorithms (GAs) is built up to predict the radiation of printed circuit boards (PCBs). This is done by introducing a dipole moment magnitude range pre-selection before the initialisation step of GAs, customising the processes of selection, crossover and mutation for anti-sticking and checking the correlation between NF and FF fitness values. Since the performance of GAs is tightly related to the number of dipoles in the GA model, FF characteristics of generic radiation sources (such as a long wire and a large loop) are analysed using both analytical calculation and source modelling by GAs. For structures with simple FF patterns, if more dipoles than necessary are used, the computational cost of GAs is unnecessarily high. On the other side, for structures with complicated FF patterns, the GA modelling may not be able to well approximate the FF radiation, due to the limitation for GAs to tackle too many unknowns. Therefore the scope of the model applicability is discussed, and a dipole number N, depending on the electrical size of the source, is recommended for GA modelling. By applying GAs to get the equivalent dipole set of a radiating PCB from the magnetic NF magnitudes, NF sampling approaches are investigated in detail, including where to locate NF sampling planes, what plane coverage angle to choose, how many points to observe, what type of data to collect, what dynamic range to allow for the data, and how many planes to choose. Two case studies are presented for predicting the FF radiation of PCBs from magnetic NF magnitude-only observations, and validate the NF sampling approaches in this thesis.
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Adnan, S. "Ultra-wideband antenna design for microwave imaging applications. Design, optimisation and development of ultra-wideband antennas for microwave near-field sensing tools, and study the matching and radiation purity of these antennas within near field environment." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5750.
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Near field imaging using microwave in medical applications has gain much attention recently as various researches show its high ability and accuracy in illuminating object comparing to the well-known screening tools such as Magnetic Resonance Imaging (MRI), digital mammography, ultrasound etc. This has encourage and motivate scientists continue to exploit the potential of microwave imaging so that a better and more powerful sensing tools can be developed.
This thesis documents the development of antenna design for microwave imaging application such as breast cancer detection. The application is similar to the concept of Ground Penetrating Radar (GPR) but operating at higher frequency band. In these systems a short pulse is transmitted from an antenna to the medium and the backscattered response is investigated for diagnose. In order to accommodate such a short pulse, a very wideband antenna with a minimal internal reflection is required. Printed monopole and planar metal plate antenna is implemented to achieve the necessary operating wide bandwidth.
The development of new compact printed planar metal plate ultra wide bandwidth antenna is presented. A generalized parametric study is carried out using two well-known software packages to achieve optimum antenna performance. The Prototype antennas are tested and analysed experimentally, in which a reasonable agreement was achieved with the simulations. The antennas present an excellent relative wide bandwidth of 67% with acceptable range of power gain between 3.5 to 7 dBi.
A new compact size air-dielectric microstrip patch-antenna designs proposed for breast cancer detection are presented. The antennas consist of a radiating patch mounted on two vertical plates, fed by coaxial cable. The antennas show a wide bandwidth that were verified by the simulations and also confirmed experimentally. The prototype antennas show excellent performance in terms the input impedance and radiation performance over the target range bandwidth from 4 GHz to 8 GHz. A mono-static model with a homogeneous dielectric box having similar properties to human tissue is used to study the interaction of the antenna with tissue. The numerical results in terms the matching required of new optimised antennas were promising.
An experimental setup of sensor array for early-stage breast-cancer detection is developed. The arrangement of two elements separated by short distance that confined equivalent medium of breast tissues were modelled and implemented. The operation performances due to several orientations of the antennas locations were performed to determine the sensitivity limits with and without small size equivalent cancer cells model.
In addition, a resistively loaded bow tie antenna, intended for applications in breast cancer detection, is adaptively modified through modelling and genetic optimisation is presented. The required wideband operating characteristic is achieved through manipulating the resistive loading of the antenna structure, the number of wires, and their angular separation within the equivalent wire assembly. The results show an acceptable impedance bandwidth of 100.75 %, with a VSWR < 2, over the interval from 3.3 GHz to 10.0 GHz. Feasibility studies were made on the antenna sensitivity for operation in a tissue equivalent dielectric medium. The simulated and measured results are all in close agreement.
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Hill, Meirian Jane. "The microwave palaeointensity technique and its application to lava." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367068.
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Adnan, Shahid. "Ultra-wideband antenna design for microwave imaging applications : design, optimisation and development of ultra-wideband antennas for microwave near-field sensing tools, and study the matching and radiation purity of these antennas within near field environment." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5750.
Full textAbstract:
Near field imaging using microwave in medical applications has gain much attention recently as various researches show its high ability and accuracy in illuminating object comparing to the well-known screening tools such as Magnetic Resonance Imaging (MRI), digital mammography, ultrasound etc. This has encourage and motivate scientists continue to exploit the potential of microwave imaging so that a better and more powerful sensing tools can be developed. This thesis documents the development of antenna design for microwave imaging application such as breast cancer detection. The application is similar to the concept of Ground Penetrating Radar (GPR) but operating at higher frequency band. In these systems a short pulse is transmitted from an antenna to the medium and the backscattered response is investigated for diagnose. In order to accommodate such a short pulse, a very wideband antenna with a minimal internal reflection is required. Printed monopole and planar metal plate antenna is implemented to achieve the necessary operating wide bandwidth. The development of new compact printed planar metal plate ultra wide bandwidth antenna is presented. A generalized parametric study is carried out using two well-known software packages to achieve optimum antenna performance. The Prototype antennas are tested and analysed experimentally, in which a reasonable agreement was achieved with the simulations. The antennas present an excellent relative wide bandwidth of 67% with acceptable range of power gain between 3.5 to 7 dBi. A new compact size air-dielectric microstrip patch-antenna designs proposed for breast cancer detection are presented. The antennas consist of a radiating patch mounted on two vertical plates, fed by coaxial cable. The antennas show a wide bandwidth that were verified by the simulations and also confirmed experimentally. The prototype antennas show excellent performance in terms the input impedance and radiation performance over the target range bandwidth from 4 GHz to 8 GHz. A mono-static model with a homogeneous dielectric box having similar properties to human tissue is used to study the interaction of the antenna with tissue. The numerical results in terms the matching required of new optimised antennas were promising. An experimental setup of sensor array for early-stage breast-cancer detection is developed. The arrangement of two elements separated by short distance that confined equivalent medium of breast tissues were modelled and implemented. The operation performances due to several orientations of the antennas locations were performed to determine the sensitivity limits with and without small size equivalent cancer cells model. In addition, a resistively loaded bow tie antenna, intended for applications in breast cancer detection, is adaptively modified through modelling and genetic optimisation is presented. The required wideband operating characteristic is achieved through manipulating the resistive loading of the antenna structure, the number of wires, and their angular separation within the equivalent wire assembly. The results show an acceptable impedance bandwidth of 100.75 %, with a VSWR < 2, over the interval from 3.3 GHz to 10.0 GHz. Feasibility studies were made on the antenna sensitivity for operation in a tissue equivalent dielectric medium. The simulated and measured results are all in close agreement.
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Imtiaz, Atif. "Quantitative materials contrast at high spatial resolution with a novel near-field scanning microwave microscope." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2469.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Zarantonello, Giorgio [Verfasser], and Christian [Akademischer Betreuer] Ospelkaus. "Robust high fidelity microwave near-field entangling quantum logic gate / Giorgio Zarantonello ; Betreuer: Christian Ospelkaus." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2020. http://d-nb.info/1214367097/34.
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Adabi, Mohammad. "Comprehensive study of large-area CVD graphene field effect structures at DC and microwave frequencies." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/45004.
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Following the successful isolation of graphene in 2004 by Novoselov and Geim, a significant amount of time and energy have been invested in studying the properties of this 2D material. Many researchers and companies from all around the world have established the vision of incorporating graphene into industrial scale applications where full utilisation of this material can be achieved outside the laboratories. One of the major technical challenges facing electrical characterisation of graphene is the different processes such as lithography and plasma etching that this material has to be exposed to before an electrical measurement can be conducted on it. These processes are known to partially deteriorate the inherent properties of graphene. A potential solution is to employ a contact-free electrical measurement technique where transport properties of large-area graphene films can be extracted without the need for realization of contacts to the surface of graphene. This thesis explores a microwave resonance technique to study the field effect properties of graphene based field effect structures. Field effect devices with a variety of dielectric films are fabricated and performance of each of them is analysed separately. This microwave method will prove to be consistent with the DC measurements and also in perfect agreement with the theoretical results from the Boltzmann equation. Further to successful demonstration of the microwave cavity technique, a novel stacked heterostructure of graphene-aluminum nitride-graphene is designed and developed. It will be shown that the sheet resistance of one graphene layer in such structure can be modulated by the application of a gate voltage to another graphene layer. This system resembles a parallel circuit of the two graphene films where each layer has a distinct doping level. The Boltzmann’s framework is used and the obtained microwave field effect conductivity result are accompanied by a fitting model. Switching ratio of as high as 4.5 is achieved at room temperature by controlling the doping level in each graphene sheet. This heterostructure system presents a promising new device structure that can potentially be used as a dual-biosensing device for biomedical applications. Such device could utilise the piezoelectric properties of aluminium nitride in combination with the strength, conductivity, transparency, and bio-compatibility of graphene to detect and measure the mass as well as the charge of various cells including the cancer cells. The dual-sensing mode is expected to significantly improve the false negatives that are currently obtained via other cell capturing methods.
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Ross, Anthony J. III. "Laser Machining and Near Field Microwave Microscopy of Silver Inks for 3D Printable RF Devices." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6944.
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3D printable materials for RF devices need improvement in order to satisfy the demand for higher frequency and lower loss performance. Characterization of materials that have shown improvements of conductor conductivity have been performed. By using a laser machining technique the loss of a 3D printed 2.45 GHz microstrip Square Open Loop Resonator (SOLR) bandpass filter has been shown to improve by 2.1dB, along with an increase in bandwidth from 10% to 12.7% when compared to a SOLR filter that has not been laser machined. Both laser machined and microwaved silver inks have been mapped for conductivity using a Near Field Microwave Microscope (NFMM) and have shown improvement of conductivity compared to inks that have been cured using standard methods.
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Abdeen, Mohammad. "Modeling of the single- and dual-gate microwave field effect transistors for computer aided design." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/29071.
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The increasing need for advanced communication technologies in the 21 st century is leading to continuous development of new and more complex active devices and systems. Transistors such as BJTs, HBTs, FETs, and HEMTs are fundamental components in today's personal, corporate and global communication systems.
The single- and dual-gate MESFETs are widely used devices with wide areas of RF/Microwave applications. Due to their superior performance, MESFETs have been extensively used in high frequency, high-gain, and low-noise amplifiers, oscillator, mixers, and many other applications.
In this thesis, conventional and intelligent modeling methodologies are investigated for the applicability to today's computer-aided design methodologies and tools. Novel approaches of this work are applied to the area of small- and large-signal modeling of the GaAs MESFET (the single- and dual-gate.)
Optimal models for the single-gate MESFET are obtained using conventional techniques. A CAD tool called, TopFinder, is developed for optimal small and large-signal model generation. The tool has been successfully tested on a commercial single-gate MESFET and HEMT transistors.
Neural network modeling technique is applied to the modeling of the dual-gate MESFET. More specifically, neural network large-signal models for the dual-gate MESFET are developed. These models present the RF device performance behavior including temperature dependence. The neural network technique is successfully applied to two dual-gate MESFET devices; a discrete chip and an on-wafer chip. First, the drain current is modeled while presenting both isothermal (using pulsed measurements) and temperature dependent neural network model for the dual-gate MESFET. A comprehensive large-signal neural network model is also developed. This model includes the nonlinearity of conductances as well as those of the junction capacitances. The nonlinear dual-gate MESFET model is successfully incorporated into ADS. The model is verified by comparing the measurements of a nonlinear single-stage amplifier application based on the dual-gate MESFET to harmonic balance simulations in ADS showing satisfactory results.
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Wu, Xiaohua. "Field simulation and calibration in external electro-optic sampling /." *McMaster only, 1996.
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