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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Relationship between the adaptive performance of antenna arrays and their underlying electromagnetic characteristics /

Gupta, Inder Jeet January 1982 (has links)
No description available.

Two-phase radio frequency heating of a plasma confined in a magnetic mirror system /

Hagenlocker, Edward Emerson January 1964 (has links)
No description available.

Time-domain simulation of electromagnetic band-gap structures using the TLM method /

Romo Luévano, Gerardo, January 1900 (has links)
Thesis (Ph.D.) - Carleton University, 2005. / Includes bibliographical references (p. 237-249). Also available in electronic format on the Internet.

Quantifying the effects of transmitter-receiver geometry variations on the capabilities of airborne electromagnetic survey systems to detect targets of high conductance /

Hefford, Shane W. January 1900 (has links)
Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 128-134). Also available in electronic format on the Internet.

Theoretical evaluation, analysis and design of surface-mounted waveguide (SMW) components for on-substrate integrated microwave applications

Schorer, Jan 07 April 2016 (has links)
This dissertation presents the research on a novel combination of well proven concepts for passive electromagnetic wave-guiding components. The goal of this work is to overcome and minimize losses occurring in frequency-selective structures. The work aims to contribute to an improvement in the application of conventional and Substrate Integrated Waveguide (SIW). It is proposed to mount conventional waveguide structures on the surface of printed circuit boards containing substrate integrated waveguides. The crossover technology is referred to as Surface Mounted Waveguide (SMW). Theoretical investigations are performed, proving the validity and superiority of the proposed structure focusing on the elimination of losses, while maintaining low space consumption and printed circuit board technology compatible manufacturing processes. Additionally, a mode matching technique is developed and successfully applied to prototype such components. The validation of this method reveals superior computational speed when compared to commercial available electromagnetic field solvers. The proposed structures are validated by measurements of several prototypes, including coupled SMW resonator filters, combined SMW and SIW resonator filters, a SMW triple-layer diplexer and single individual SMW resonator filters. The experimental verification shows good agreement between theory and measurements. Moreover, the comparison to other technologies proves the superiority of the proposed structures. / Graduate

Finite-element determination of two-axis transient parameters for the simulation of turbine-generators

Escarela Perez, Rafael January 1996 (has links)
No description available.

Operational assessment of Target Acquisitions Weapons Software (TAWS) prediction performance at Nellis AFB, NV

Hernandez, Jerome H. 03 1900 (has links)
Target Acquisition Weapons Software (TAWS) Version 3.4 is a joint Tactical Decision Aid (TDA) used to predict performance of electro-optic and electro-magnetic (EM/EO) munitions and navigation systems. TAWS is the USAF and USN mission-planning standard for laser-guided, infrared, and TV munitions and navigation systems TDAs. As TAWS continues to deploy through the mission planning community there is a need to establish a systematic approach to assessing TAWS accuracy. This study was an operational assessment of TAWS Infrared (IR) model performance and consisted of two parts: a comparison of model predictions to pilot observations of IR detection range of a static tank target and an assessment of physical temperature predictions. Limiting factors of this project are similar to those encountered in real world utilization of TAWS mission planning TDAs. This evaluation found TAWS predicted detection ranges and target scene model output were representative forecasts of observed values. The TDA provided a good description of background thermal behavior and highlighted the necessity of careful evaluation of the target scene because of component facet complexity and the geometry of facets exposed to the sensor view. The resulting component analysis illuminated the benefit of focusing new TAWS development on improving the target physical model.

Modelling induced fields in the human body exposed to electric fields from high voltage transmission lines designed to meet 10 kV/m at ground level

Hubbard, Kenneth Roy January 2017 (has links)
A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, February 2017 / There has been increasing public concern regarding adverse health effects due to power frequency electric and magnetic fields. Safety guidelines/standards for electric and magnetic field exposures have been established by different public organizations. However, the link between low frequency (power frequency) electric and magnetic field exposure and adverse health effects is not yet well established. Limits on human exposure to low frequency electric and magnetic fields are fundamentally specified for in-situ fields in tissues/organs. These dosimetric limits are referred to as Basic Restrictions for protection against potentially adverse effects from electro-stimulation. In addition, secondary limits, the exposure Reference Levels in environmental electric and magnetic fields are also given for practical compliance purposes. These are generally derived from the Basic Restrictions based on uniform-fields with a provision that the Basic Restrictions must be observed for non-uniform cases. In practice, any structure influences the electric fields in High Voltage systems, and thus creates electric field non-uniformity. The human exposure of the general public to electric fields from Eskom’s 765 kV transmission network operating at 50 Hz, is addressed through physical measurements, theoretical predictions and 3-D human model dosimetry, which is presented in this dissertation. / MT 2017

Field enhancement using noble metal structures. / 用貴金屬結構增強場強 / CUHK electronic theses & dissertations collection / Field enhancement using noble metal structures. / Yong gui jin shu jie gou zeng qiang chang qiang

January 2012 (has links)
共振是自然界一個基本物理過程。特別是,在納米尺度上的光頻電磁諧振產生顯著的場增強,提供了一種手段來影響和控制光與物質的相互作用。例如,巨大的場增強使表面增強拉曼散射具有探測單個分子的靈敏度。此外,場增強可以使發光二極體具有更高亮度高,但輸入功率更低。雖然場增強在一些關鍵技術領域大有前途,有許多挑戰仍有待解決。由於場增強是如此強烈地依賴系統的幾可形狀即使稍作修改可以導致大的結果變化,因此理解幾何結構如何影響場增強和可重複的製造這些車前壽是最重要的。因此本論文致力於設計,製造和貴金屬如銀或金的一維結構的表面上生成的場增強特性。 / 首先對s-偏振下一維金屬光栅產生的場增強使用嚴格購合波分析(RCWA) 進行了設計和優化。優化後,在514nm 波長最強的增強因數是9.7 。製作了一維光栅並進行角度相關的反射率測量,實驗結果與理論計算相符。 / 對一種新型利用表面等離子激元的呻吟加強電場的單縫桔構進行了研究。首先利用用衰減全反射搞合在50 納米厚的金屬薄膜上產生sp恥,隨後利用spps 驅動這一狹縫。結果發現縫內場增強至少3 倍於狹縫附近的等離子激元背景。其增強機理用數值和分析的方法進行理論研究。 / 提出了兩種新型的製造高深寬比納米縫隙的簡便方法。一個是在飯有金膜的薄玻璃上製造裂紋,獲得了寬度小於5nm 具有一定平整度的抗縫,通過掃描電子顯微鏡圖像和共焦雙光子發射(CTPE) 光譜和時間域有限差分模擬的對比得到了確認。另一種是對鍍有金膜的柔性基底進行疲勞彎折,獲得了大量狹縫。觀察到CTPE 和二次諧波產生從這些縫中產生。 / 採用電子束光刻製作了納米縫並使用CTPE 進行了表徵。提出一種新方法對激發波長和發射波長的增強因數進行了分解。發現脈衝錯射能調整EBL 樣品的共振波長到錯射波長。提出了一種機制解釋這一現像。進一步實驗表明這是一種製造任意共振波長場增強熱點的有用方法。 / Resonance may be one of the most fundamental rules of nature. Electromagnetic resonance at nanometer scale could produce a giant field enhancement at optical frequency, providing a way to measure and control the process of atoms and molecules at single molecule scale. For example, the giant field enhancement would provide single molecule sensitivity for Raman scattering, which provides unique tools in measuring the quantity in extremely low concentration. In addition, light-emitting diodes could have high brightness but low input power that would be revolutionary in the optoelectronic industry. Although light enhancement is promising in several key technology areas, there are several challenges remain to be tackled. In particular, since the field enhancement is so strongly geometry dependent that slight modification of the geometry can lead to large variations in the outcome, a thorough understanding in how the geometry of the structure affects the field enhancement and creating proper methods to fabricate these structures reproducibly is of most importance. This thesis is devoted to design, fabrication and characterization of field enhancement generated on the surface of noble metals such as silver or gold with 1D structure. / The s-polarized field enhancement arISIng from one-dimensional metal gratings IS designed and optimized by using Rigorous Coupling Wave Analysis (RCWA). After optimization, the strongest enhancement factor is found to be 9.7 for 514nm wavelength light. The theoretical results are confirmed by angle-dependent reflectivity measurements and the experimental results are found to support the theory. / A novel single slit structure employing sUlface plasmon polaritons (SPPs) for enhancing the electric field is studied. SPPs are first generated on a 50 nm thick metal film using attenuated total reflection coupling, and they are subsequently coupled to the cavity mode induced by the single slit. As a result, the field enhancement is found at least 3 times the surface plasmon background adjacent to the slit, as predicted by using RCWA. The mechanism for enhancement is theoretically studied both numerically and analytically. / Two novel convenient methods for fabricating nanoslits with high aspect ratio are proposed. One is creating nanoslits by cracking the thin glass substrates with metal film. Sub-Snm wide slits with fair uniformity are created, as confirmed by Scanning Electron Microscopy images and comparing the Confocal Two Photon Emission (CTPE) spectroscopy with finite difference in time domain simulations. The other is creating slits by fatiguing the metal film on a flexible substrate. Enhanced CTPE and second harmonic generation are observed arising from these less than 20nm wide slits. / Nanoslits fabricated using Electron Beam Lithography (EBL) are characterized using CTPE. The overall emission enhancement of excitation and collection wavelengths is separated by a proposed method. It is surprisingly found that the pulsing laser can tune the resonant wavelength of the EBL samples to the laser wavelength. A mechanism is proposed for this phenomenon. It is shown this can be developed into a tool to fabricate field enhancement hot spots. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Liu, Benliang = 用貴金屬結構增強場強 / 劉本良. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 133-137). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Liu, Benliang = Yong gui jin shu jie gou zeng qiang chang qiang / Liu Benliang. / Acknowledgement --- p.i / Abstract --- p.ii / 摘要 --- p.iv / List of figures --- p.1 / Chapter 1 --- Overview --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Applications of field enhancement --- p.1 / Chapter 1.2.1 --- Surface enhanced Raman scattering --- p.1 / Chapter 1.2.2 --- Enhanced luminescence --- p.4 / Chapter 1.3 --- Fundamentals of field enhancement --- p.5 / Chapter 1.3.1 --- The Maxwell's equations --- p.6 / Chapter 1.3.2 --- Boundary conditions --- p.8 / Chapter 1.3.3 --- Phase matching condition --- p.10 / Chapter 1.3.4 --- Dipole --- p.11 / Chapter 1.3.5 --- Purcell factor --- p.12 / Chapter 1.3.6 --- Mode and mode interaction --- p.13 / Chapter 1.3.7 --- Surface plasmon resonance --- p.14 / Chapter 1.3.8 --- Fabry-Perot cavity resonance --- p.16 / Chapter 1.4 --- Overview of the nanofabrication methods of metal structures for field enhancement --- p.17 / Chapter 1.4.1 --- Photolithography --- p.18 / Chapter 1.4.2 --- Electron Beam Lithography --- p.20 / Chapter 1.4.3 --- Focused ion beam --- p.21 / Chapter 1.4.4 --- Summary --- p.21 / Chapter 2 --- Methods of simulation --- p.26 / Chapter 2.1 --- Rigorous coupled wave analysis framework --- p.26 / Chapter 2.1.1 --- FormulaofRCWA --- p.26 / Chapter 2.1.2 --- Expression ofMaxwell's equations in Fourier space --- p.27 / Chapter 2.1.3 --- Numerical shooting method --- p.29 / Chapter 2.1.4 --- Reflection efficiency, transmission efficiency and absorption --- p.32 / Chapter 2.1.5 --- Convergence test of the RCWA simulation --- p.33 / Chapter 2.2 --- Finite difference in time domain --- p.34 / Chapter 2.2.1 --- Formulations of FDTD --- p.34 / Chapter 2.2.2 --- Dispersion of dielectric constant --- p.35 / Chapter 2.2.3 --- Boundary conditions and excitation sources --- p.37 / Chapter 3 --- Investigation of s-polarized resonance on 1D grating --- p.40 / Chapter 3.1 --- Introduction --- p.40 / Chapter 3.2 --- Theoretical results of the s-polarized resonance in the 1D grating --- p.41 / Chapter 3.3 --- Discussion of the theoretical results --- p.47 / Chapter 3.3.1 --- Origination of the s-polarized resonance modes --- p.47 / Chapter 3.3.2 --- Position discrepancy between absorption peaks and reflection dips --- p.48 / Chapter 3.3.3 --- Absorption beyond the cutoff wavelength of reflectance --- p.48 / Chapter 3.3.4 --- Absorption wavelength dependency on the periodicity --- p.50 / Chapter 3.4 --- Effects of parameters on absorption and electric field --- p.50 / Chapter 3.5 --- Optimization the s-polarized resonance for field enhancement --- p.54 / Chapter 3.6 --- Angle dependency of the optimized resonant mode --- p.55 / Chapter 3.7 --- Grating preparation and characterization --- p.57 / Chapter 3.8 --- Experimental results and discussion --- p.59 / Chapter 3.9 --- Summary --- p.73 / Reference --- p.74 / Chapter 4 --- Fabricating and characterizing nanoslit-shaped resonant cavity --- p.75 / Chapter 4.1 --- Introduction --- p.75 / Chapter 4.2 --- Confocal two photon emission measurement --- p.78 / Chapter 4.2.1 --- Background --- p.78 / Chapter 4.2.2 --- Polarization dependence of the confocal system --- p.79 / Chapter 4.3 --- Decomposition of excitation and collection TPL enhancement --- p.81 / Chapter 4.4 --- Fabrication and characterization of slits by cracking glass substrate --- p.83 / Chapter 4.4.1 --- Fabrication of nanoslits by cracking glass --- p.83 / Chapter 4.4.2 --- Characterization of the nanoslits by cracking glass substrates --- p.86 / Chapter --- Two-photon emission from rough slits 86 / Chapter --- Location dependence of the two-photon emission --- p.87 / Chapter --- Relation between reflection and two-photon emission --- p.88 / Chapter --- Wavelength dependence ofTPLfrom the slits by cracking glass --- p.89 / Chapter 4.4.3 --- Discussion --- p.97 / Chapter 4.4.4 --- Summary --- p.98 / Chapter 4.5 --- Fabrication and characterization of nanoslits by fatigue --- p.98 / Chapter 4.5.1 --- Fabrication ofnanoslits by fatigue --- p.98 / Chapter 4.5.2 --- Characterization ofnanoslits by fatigue --- p.100 / Chapter 4.5.3 --- Discussion --- p.105 / Chapter 4.6 --- Two photon emission from nanoslits by EBL --- p.106 / Chapter 4.6.1 --- Sample preparation --- p.107 / Chapter 4.6.2 --- Characterization of the slits made by Electron Beam Lithography --- p.109 / Chapter --- Reflected light extinction and two photon emission --- p.109 / Chapter --- Wavelength dependence of TPL enhancement --- p.120 / Chapter --- Laser modification of resonant wavelength of the cavity --- p.124 / Chapter --- Discussion --- p.126 / Chapter 4.6.3 --- Summary --- p.132 / Chapter 5 --- Conclusion --- p.138

Electromagnetic Field Modeling of Transcranial Electric and Magnetic Stimulation: Targeting, Individualization, and Safety of Convulsive and Subconvulsive Applications

Deng, Zhi-De January 2013 (has links)
The proliferation of noninvasive transcranial electric and magnetic brain stimulation techniques and applications in recent years has led to important insights into brain function and pathophysiology of brain-based disorders. Transcranial electric and magnetic stimulation encompasses a wide spectrum of methods that have developed into therapeutic interventions for a variety of neurological and psychiatric disorders. Although these methods are at different stages of development, the physical principle underlying these techniques is the similar. Namely, an electromagnetic field is induced in the brain either via current injection through scalp electrodes or via electromagnetic induction. The induced electric field modulates the neuronal transmembrane potentials and, thereby, neuronal excitability or activity. Therefore, knowledge of the induced electric field distribution is key in the design and interpretation of basic research and clinical studies. This work aims to delineate the fundamental physical limitations, tradeoffs, and technological feasibility constraints associated with transcranial electric and magnetic stimulation, in order to inform the development of technologies that deliver safer, and more spatially, temporally, and patient specific stimulation. Part I of this dissertation expounds on the issue of spatial targeting of the electric field. Contrasting electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) configurations that differ markedly in efficacy, side effects, and seizure induction efficiency could advance our understanding of the principles linking treatment parameters and therapeutic outcome and could provide a means of testing hypotheses of the mechanisms of therapeutic action. Using the finite element method, we systematically compare the electric field characteristics of existing forms of ECT and MST. We introduce a method of incorporating a modality-specific neural activation threshold in the electric field models that can inform dosage requirements in convulsive therapies. Our results indicate that the MST electric field is more focal and more confined to the superficial cortex compared to ECT. Further, the conventional ECT current amplitude is much higher than necessary for seizure induction. One of the factors important to clinical outcome is seizure expression. However, it is unknown how the induced electric field is related to seizure onset and propagation. In this work, we explore the effect of the electric field distribution on the quantitative ictal electroencephalography and current source density in ECT and MST. We further demonstrate how the ECT electrode shape, size, spacing, and current can be manipulated to yield more precise control of the induced electric field. If desirable, ECT can be made as focal as MST while using simpler stimulation equipment. Next, we demonstrate how the electric field induced by transcranial magnetic stimulation (TMS) can be controlled. We present the most comprehensive comparison of TMS coil electric field penetration and focality to date. The electric field distributions of more than 50 TMS coils were simulated. We show that TMS coils differ markedly in their electric field characteristics, but they all are subject to a consistent depth--focality tradeoff. Specifically, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electric field spread. Figure-8 type coils are fundamentally more focal compared to circular type coils. Understanding the depth--focality tradeoff can help researchers and clinicians to appropriately select coils and interpret TMS studies. This work also enables the development of novel TMS coils with electronically switchable active and sham modes as well as for deep TMS. Design considerations of these coils are extensively discussed. Part II of the dissertation aims to quantify the effect of individual, sex, and age differences in head geometry and conductivity on the induced neural stimulation strength and focality of ECT and MST. Across and within ECT studies, there is marked unexplained variability in seizure threshold and clinical outcomes. It is not known to what extent the age and sex effects on seizure threshold are mediated by interindividual variation in neural excitability and/or anatomy of the head. Addressing this question, we examine the effect on ECT and MST induced field characteristics of the variability in head diameter, scalp and skull thicknesses and conductivities, as well as brain volume, in a range of values that are representative of the patient population. Variations in the local tissue properties such as scalp and skull thickness and conductivity affect the existing ECT configurations more than MST. On the other hand, the existing MST coil configurations show greater sensitivity to head diameter variation compared to ECT. Due to the high focality of MST compared to ECT, the stimulated brain volume in MST is more sensitive to variation in tissue layer thicknesses. We further demonstrate how individualization of the stimulus pulse current amplitude, which is not presently done in ECT or MST, can be used as a means of compensating for interindividual anatomical variability, which could lead to better and more consistent clinical outcomes. Part III of the dissertation aims to systemically investigate, both computationally and experimentally, the safety of TMS and ECT in patients with a deep-brain stimulation system, and propose safety guidelines for the dual-device therapy. We showed that the induction of significant voltages in the subcutaneous leads in the scalp during TMS could result in unintended and potentially dangerous levels of electrical currents in the DBS electrode contacts. When applying ECT in patients with intracranial implants, we showed that there is an increase in the electric field strength in the brain due to conduction through the burr holes, especially when the burr holes are not fitted with nonconductive caps. Safety concerns presently limit the access of patients with intracranial electronic devices to therapies involving transcranial stimulation technology, which may preclude them from obtaining appropriate medical treatments. Gaining better understanding of the interactions between transcranial and implanted stimulation devices will demarcate significant safety risks from benign interactions, and will provide recommendations for reducing risk, thus enhancing the patient's therapeutic options.

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