10 research outputs found

    Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits

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    In this dissertation, accurate and efficient numerical algorithms are developed to incorporate the feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits. First, simulation of an antenna system requires accurate modeling of interactions between the radiating elements and the associated feeding network. In this work, a feed network is represented in terms of its scattering matrix in a rational function form in the frequency domain that enables its interfacing with the time-domain finite element modeling of the antenna elements through a fast recursive time-convolution algorithm. The exchange of information between the antenna elements and the feed network occurs through the incident and reflected modal voltages/currents at properly defined port interfaces. The proposed numerical scheme allows a full utilization of the advanced antenna simulation techniques, and significantly extends the current antenna modeling capability to the system level. Second, a hybrid field-circuit solver that combines the capabilities of the time-domain finite element method and a lumped circuit analysis is developed for accurate and efficient characterization of complicated microwave circuits that include both distributive and lumped-circuit components. The distributive portion of the device is modeled by the time-domain finite element method to generate a finite element subsystem, while the lumped circuits are analyzed by a SPICE-like circuit solver to generate a circuit subsystem. A global system for both the finite-element and circuit unknowns is established by combining the two subsystems through coupling matrices to model their interactions. For simulations of even more complicated mixed-scale circuit systems that contain pre-characterized blocks of discrete circuit elements, the hybrid field-circuit analysis implemented a systematic and efficient algorithm to incorporate multiport lumped networks in terms of frequency-dependent admittance matrices. Other advanced features in the hybrid field-circuit solver include application of the tree-cotree splitting algorithm and introduction of a flexible time-stepping scheme. Various numerical examples are presented to validate the implementation and demonstrate the accuracy, efficiency, and applications of the proposed numerical algorithms

    Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

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    Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

    Spectral Element Method Simulation of Linear and Nonlinear Electromagnetic Field in Semiconductor Nanostructures

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    <p>In this dissertation, the spectral element method is developed to simulate electromagnetic field in nano-structure consisting of dielectric, metal or semiconductor. The spectral element method is a special kind of high order finite element method, which has spectral accuracy. When the order of the basis function increases, the accuracy increases exponentially. The goal of this dissertation is to implement the spectral element method to calculate the electromagnetic properties of various semiconductor nano-structures, including photonic crystal, photonic crystal slab, finite size photonic crystal block, nano dielectric sphere. The linear electromagnetic characteristics, such as band structure and scattering properties, can be calculated by this method with high accuracy. In addition, I have explored the application of the spectral element method in nonlinear and quantum optics. The effort will focus on second harmonic generation and quantum dot nonlinear dynamics. </p><p>The electromagnetic field can be simulated in both frequency domain and time domain. Each method has different application for research and engineering. In this dissertation, the first half of the dissertation discusses the frequency domain solver, and the second half of the dissertation discusses the time domain solver.</p><p>For frequency domain simulation, the basic equation is the second order vector Helmholtz equation of the electric field. This method is implemented to calculate the band structure of photonic crystals consisting of dielectric material as well as metallic materials. Because the photonic crystal is periodic, only one unit cell need to be simulated in the computational domain, and a periodic boundary condition is applied. The spectral accuracy is inspected. Adding the radiation boundary condition at top and bottom of the computational region, the scattering properties of photonic crystal slab can be calculated. For multiple layers photonic crystal slab, the block-Thomas algorithm is used to increase the efficiency of the calculation. When the simulated photonic crystals are finite size, unlike an infinitely periodic system, the periodic boundary condition does not apply. In order to increase the efficiency of the simulation, the domain decomposition method is implemented. </p><p>The second harmonic generation, which is a kind of nonlinear optical effect, is simulated by the spectral element method. The vector Helmholtz equations of multiple frequencies are solved in parallel and the consistence solution with nonlinear effect is obtained by iterative solver. The sensitivity of the second harmonic generation to the thickness of each layer can be calculated by taking the analytical differential of the equation to the thickness of each element. </p><p>The quantum dot dynamics in semiconductor are described by the Maxwell-Bloch equations. The frequency domain Maxwell-Bloch equations are deduced. The spectral element method is used to solve these equations to inspect the steady state quantum dot dynamic behaviors under the continuous wave electromagnetic excitation.</p><p>For time domain simulation, the first order curl equations in Maxwell equations are the basic equations. A spectral element method based on brick element is implemented to simulate a nano-structure consisting of woodpile photonic crystal. The resonance of a micro-cavity consisting of a point defect in the woodpile photonic crystal block is simulated. In addition, the time domain Maxwell-Bloch equations are implemented in the solver. The spontaneous emission process of quantum dot in the micro-cavity is inspected. </p><p>Another effort is to implement the Maxwell-Bloch equations in a previously implemented domain decomposition spectral element/finite element time domain solver. The solver can handle unstructured mesh, which can simulate complicated structure. The time dependent dynamics of a quantum dot in the middle of a nano-sphere are investigated by this implementation. The population inversion under continuous and pulse excitation is investigated. </p><p>In conclusion, the spectral element method is implemented for frequency domain and time domain solvers. High efficient and accurate solutions for multiple layers nano-structures are obtained. The solvers can be applied to design nano-structures, such as photonic crystal slab resonators, and nano-scale semiconductor lasers.</p>Dissertatio

    1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

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    A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

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    Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

    The religious and theological foundations of natural science

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    This thesis examines the religions and theological foundations of natural science. A mythology has arisen, both popularly and academieally, that locates the historical origins of science in the great humanistic movements of the Renaissance and Eniightenment. Conversely Calvinism and Puritenism are regarded as regressive forces, the enemies of freedom and progress, interested only in rigerons morality and otherwordly piety. Philosophically there is a wide spread divorce between faith and knowledge, religion and science, while sociologically science is seen to advance with the shaking off of the fetters of religious belief. The choice of approach was difficult. I elected for an overview rather than an exhaustive detail of one aspect. This was a choice against specialisation and the abstreative loss of concrete reality. It alse seems more consonant with the topic under consideration. The major divisions are as follows: Part I: An historical section which contextualises the study and indicates origins and motivations of modern science in religious interests - particularly Calvinism. By the nature of such a study there is a degree of ambivalence. Part II: The thesis is established by a review and brief eritique of secular philosophies of sciences. This again is ambivalent though I have scught to plant signposts to the clearer statement presented in Part IV. Part III: A survey of Christian responses to the topic. While remaining within Protestant thought I have tried to do justice to as many divergent positions as is consistent with overall coherence. Part IV: this seeks to establish the religious and theological foundations of natural science on Christian perspectival grounds - viewing religion as the crientation of the heart in a basic commitment to the universe: and seeing in the theology of the sovereignty of God, His law, the dectrines of creation and cultural activity, clear motivations to scientific activity. So this is the crux of my thesis. I also give some practical application in terms of the problems of the environment and technic, and how the fundamental issues pertain therein. I believe the basic contribution to the subject is not, in the first instance, detailed originality but in an original synthesis of materil. Detailed contributions are inter alia: 1. A critical introduction to the thought of 'Cosmonomiem' where that impinges on my topic. The study, based within the parameters of nesyeweerd's 'Cosmonomic Idea', seeks to apply cosmonomism in a more scientific field than that in which most of its proponents work. 2. More specifically I point to my suggested solution of Mackay's complementary model of science and relgions; 3. My causal-perspectival interpretation of the influence of Calvin(ism) which goes further than Merton, Neekyaas or Torrance. 4. My critique of the theological spectrum - liberal and evangelical. I point particularly to my analysis of erangelicals who are largely uncritiqued from within their own perspective and ignored by liberals, despite their vest amount of literature on science and belief; and 5. The exposure of a confusion between 'science' and 'scientia' ; and between 'religion', 'theology' and 'faith'. Inter alia my conclusions include: 1. Religion and natural science (but not theology and natural science) are not separate entities, for the former founds and activates the latter. The whole discussion of science 'and' religion/belief is a false dichotomy and therefore a pseudo-problem. 2. The religious foundation of science does not dictate/coereo scientific scientific theories. While it can give a definite 'no' to some theories, it can only give a conditional 'yes' to theories. 3. There is, strictly speaking, no 'theology of science' but a theological framework within which science can be understood. 4. Unnecessary conceptual problems have been created by seeing laws of nature as antonomous from the law of God. 5. 'The' scientific method is mythological
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