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- Title
- PLANAR MAGNETICS DESIGN FOR LOW-VOLTAGEDC-DC CONVERTERS.
- Creator
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Xiao, Shangyang, Wu, Thomas X., University of Central Florida
- Abstract / Description
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The objectives of this thesis are to design planar magnetic devices based on accurate electromagnetic analysis and miniaturize magnetics within desired low profile as well as small footprint. A novel methodology based on FEM simulation is proposed. By introducing Maxwell 2D simulator, optimal interleaving structures can be found to reduce AC losses that cannot otherwise be accounted for by conventional method. And 3D simulator is employed to make the results more realistic. Thus, high...
Show moreThe objectives of this thesis are to design planar magnetic devices based on accurate electromagnetic analysis and miniaturize magnetics within desired low profile as well as small footprint. A novel methodology based on FEM simulation is proposed. By introducing Maxwell 2D simulator, optimal interleaving structures can be found to reduce AC losses that cannot otherwise be accounted for by conventional method. And 3D simulator is employed to make the results more realistic. Thus, high-efficiency high-power density magnetics is achieved.
Show less - Date Issued
- 2004
- Identifier
- CFE0000075, ucf:46120
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000075
- Title
- FINITE ELEMENT METHOD MODELING OF ADVANCED ELECTRONIC DEVICES.
- Creator
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Chen, Yupeng, Wu, Thomas, University of Central Florida
- Abstract / Description
-
In this dissertation, we use finite element method together with other numerical techniques to study advanced electron devices. We study the radiation properties in electron waveguide structure with multi-step discontinuities and soft wall lateral confinement. Radiation mechanism and conditions are examined by numerical simulation of dispersion relations and transport properties. The study of geometry variations shows its significant impact on the radiation intensity and direction. In...
Show moreIn this dissertation, we use finite element method together with other numerical techniques to study advanced electron devices. We study the radiation properties in electron waveguide structure with multi-step discontinuities and soft wall lateral confinement. Radiation mechanism and conditions are examined by numerical simulation of dispersion relations and transport properties. The study of geometry variations shows its significant impact on the radiation intensity and direction. In particular, the periodic corrugation structure exhibits strong directional radiation. This interesting feature may be useful to design a nano-scale transmitter, a communication device for future nano-scale system. Non-quasi-static effects in AC characteristics of carbon nanotube field-effect transistors are examined by solving a full time-dependent, open-boundary Schrödinger equation. The non-quasi-static characteristics, such as the finite channel charging time, and the dependence of small signal transconductance and gate capacitance on the frequency, are explored. The validity of the widely used quasi-static approximation is examined. The results show that the quasi-static approximation overestimates the transconductance and gate capacitance at high frequencies, but gives a more accurate value for the intrinsic cut-off frequency over a wide range of bias conditions. The influence of metal interconnect resistance on the performance of vertical and lateral power MOSFETs is studied. Vertical MOSFETs in a D2PAK and DirectFET package, and lateral MOSFETs in power IC and flip chip are investigated as the case studies. The impact of various layout patterns and material properties on RDS(on) will provide useful guidelines for practical vertical and lateral power MOSFETs design.
Show less - Date Issued
- 2006
- Identifier
- CFE0001389, ucf:46987
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001389
- Title
- RF LOW PASS FILTER DESIGN AND FABRICATION USING INTEGRATED PASSIVE DEVICE TECHNOLOGY.
- Creator
-
Li, Heli, Wu, Thomas, University of Central Florida
- Abstract / Description
-
In this thesis, the whole process of design a low pass filter (LPF) for the wireless communication application has been presented. Integrated passive device technology based on GaAs substrate has been utilized to make the LPF. Schematic simulation and electromagnetic simulations are extensively used in the design process. EM simulation is used in the selection of layout design and processing parameters for design optimization of both the inductors and IPD harmonic filters. The effective use...
Show moreIn this thesis, the whole process of design a low pass filter (LPF) for the wireless communication application has been presented. Integrated passive device technology based on GaAs substrate has been utilized to make the LPF. Schematic simulation and electromagnetic simulations are extensively used in the design process. EM simulation is used in the selection of layout design and processing parameters for design optimization of both the inductors and IPD harmonic filters. The effective use of EM simulation enables us to realize the successful development of high performance harmonic filters. To make the optimization be more flexible and also for a deeper understanding of the optimization theory, optimization using genetic algorithm is also implemented. The weight of each targets are adjustable, and a non-uniformly distributed goal for the harmonic rejection range is introduced to achieve better optimization results. The embedded LPF is built and measurement results show good agreement with the simulation data. This kind of very compact, high performance harmonic filters can be used in radio transceiver front-end modules. The realized harmonic filters have insertion loss less than 0.6 dB and harmonic rejections greater than 25 dB with a compact die size of 0.8 mm2.
Show less - Date Issued
- 2006
- Identifier
- CFE0001466, ucf:47091
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001466
- Title
- MAGNETICS DESIGN FOR HIGH CURRENT LOW VOLTAGE DC/DC CONVERTER.
- Creator
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zhou, hua, Wu, Thomas Xinzhang, University of Central Florida
- Abstract / Description
-
With the increasing demand for small and cost efficient DC/DC converters, the power converters are expected to operate with high efficiency. Magnetics components design is one of the biggest challenges in achieving the higher power density and higher efficiency due to the significant portion of magnetics components volume in the whole power system. At the same time, most of the experimental phenomena are related to the magnetics components. So, good magnetics components design is one of the...
Show moreWith the increasing demand for small and cost efficient DC/DC converters, the power converters are expected to operate with high efficiency. Magnetics components design is one of the biggest challenges in achieving the higher power density and higher efficiency due to the significant portion of magnetics components volume in the whole power system. At the same time, most of the experimental phenomena are related to the magnetics components. So, good magnetics components design is one of the key issues to implement low voltage high current DC/DC converter. Planar technology has many advantages. It has low profile construction, low leakage inductance and inter-winding capacitance, excellent repeatability of parasitic properties, cost efficiency, great reliability, and excellent thermal characteristics. On the other side, however, planar technology also has some disadvantages. Although it improves thermal performance, the planar format increases footprint area. The fact that windings can be placed closer in planar technology to reduce leakage inductance also often has an unwanted effect of increasing parasitic capacitances. In this dissertation, the planar magnetics designs for high current low voltage applications are thoroughly investigated and one CAD design methodology based on FEA numerical analysis is proposed. Because the frequency dependant parasitic parameters of magnetics components are included in the circuit model, the whole circuit analysis is more accurate. When it is implemented correctly, integrated magnetics technique can produce a significant reduction in the magnetic core content number and it can also result in cost efficient designs with less weight and smaller volume. These will increase the whole converter's power density and power efficiency. For high output current and low output voltage applications, half bridge in primary and current doublers in secondary are proved to be a very good solution. Based on this topology, four different integrated magnetics structures are analyzed and compared with each other. One unified model is introduced and implemented in the circuit analysis. A new integrated magnetics component core shape is proposed. All simulation and experimental results verify the integrated magnetics design. There are several new magnetics components applications shown in the dissertation. Active transient voltage compensator is a good solution to the challenging high slew rate load current transient requirement of VRM. The transformer works as an extra voltage source. During the transient periods, the transformer injects or absorbs the extra transient to or from the circuit. A peak current mode controlled integrated magnetics structure is proposed in the dissertation. Two transformers and two inductors are integrated in one core. It can force the two input capacitors of half bridge topology to have the same voltage potential and solve the voltage unbalance issue. The proposed integrated magnetics structure is simple compared with other methods implementing the current mode control to half bridge topology. Circuit analysis, simulation and experimental results verify the feasibility of these applications.
Show less - Date Issued
- 2007
- Identifier
- CFE0001823, ucf:47341
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001823
- Title
- ANALYSIS AND DESIGN OF MINIATURIZED RF SAW DUPLEXER PACKAGE.
- Creator
-
Dong, Hao, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This dissertation provides a comprehensive methodology for accurate analysis and design of miniaturized radio frequency (RF) surface acoustic wave (SAW) duplexer package. Full-wave analysis based on the three dimensional (3-D) finite element method (FEM) is successfully applied to model the package. The die model is obtained by combining the acoustics and die busbars parasitics models. The acoustics model is obtained using the coupling-of-models (COM) technique. The die busbars, bonding wires...
Show moreThis dissertation provides a comprehensive methodology for accurate analysis and design of miniaturized radio frequency (RF) surface acoustic wave (SAW) duplexer package. Full-wave analysis based on the three dimensional (3-D) finite element method (FEM) is successfully applied to model the package. The die model is obtained by combining the acoustics and die busbars parasitics models. The acoustics model is obtained using the coupling-of-models (COM) technique. The die busbars, bonding wires and printed circuit board (PCB) are modeled using full-wave analysis. After that, the models of package, die, and bonding wires are assembled together to get the total response. To take into account the mutual couplings, the methodology is extended to model the package, die busbars, and bonding wires together. The advantages and disadvantages of the methodology are also discussed. Based on the methodology, the Korea personal communication system (KPCS) duplexer is analyzed and designed. The isolation of KPCS duplexer package is significantly improved by redesigning inner ground plane, bonding wire scheme and ground via. A KPCS duplexer package is designed and excellent transmitter to receiver isolation in the transmission band is achieved. Simulation and measurement results are compared, and excellent agreement is found. Although we focus on investigating the methods to improve the isolation, the passband performance is also improved. The methodology is also successfully used for flip chip duplexer. The simulation results from our assembling method match the measurement results very well. Optimization method is applied to improve the transmit band isolation. With the new package and die design, the transmit band isolation can be improved from -53.6 dB to -65.2 dB. Based on the new package, the effect of the Rx ground trace on the isolation is investigated and the transmit band isolation can achieve -67.3 dB with the modification of the Rx ground trace. The technique developed in this dissertation reduces the design cycle time greatly and can be applied to various RF SAW device packages.
Show less - Date Issued
- 2005
- Identifier
- CFE0000688, ucf:46493
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000688
- Title
- FINITE ELEMENT ANALYSIS OF LEFT-HANDED WAVEGUIDES.
- Creator
-
Vellakkinar Balasubramaniam, Satish, Wu, Thomas X, University of Central Florida
- Abstract / Description
-
In this work, waveguides with simultaneous negative dielectric permittivity and magnetic permeability, otherwise known as left-handed waveguides, are investigated. An approach of formulating and solving an eigenvalue problem with finite element method resulting in the dispersion relation of the waveguides is adopted in the analysis. Detailed methodology of one-dimensional scalar and two-dimensional vector finite element formulation for the analysis of grounded slab and arbitrary shaped...
Show moreIn this work, waveguides with simultaneous negative dielectric permittivity and magnetic permeability, otherwise known as left-handed waveguides, are investigated. An approach of formulating and solving an eigenvalue problem with finite element method resulting in the dispersion relation of the waveguides is adopted in the analysis. Detailed methodology of one-dimensional scalar and two-dimensional vector finite element formulation for the analysis of grounded slab and arbitrary shaped waveguides is presented. Based on the analysis, for waveguides with conventional media, excellent agreement of results is observed between the finite element approach and the traditional approach. The method is then applied to analyze left-handed waveguides and anomalous dispersion of modes is found. The discontinuity structure of a left-handed waveguide sandwiched between two conventional dielectric slab waveguides is analyzed using mode matching technique and the results are discussed based on the inherent nature of the materials. The scattering characteristics of a parallel plate waveguide partially filled with left-handed and conventional media are also analyzed using finite element method with eigenfunction expansion technique.
Show less - Date Issued
- 2004
- Identifier
- CFE0000296, ucf:46208
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000296
- Title
- DSP IMPLEMENTATION OF DC VOLTAGE REGULATION USING ADAPTIVE CONTROL FOR 200 KW 62000 RPM INDUCTION GENERATOR.
- Creator
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Elkhomri, Othman, Wu, Thomas, University of Central Florida
- Abstract / Description
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The thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship...
Show moreThe thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship has been modeled using adaptive control technique to vary the gains automatically at any load condition. The adaptive control technique has been successfully generalized for real time DSP implementation to regulate the DC voltage for high speed induction generators rated from 5 kW to 200 kW.
Show less - Date Issued
- 2006
- Identifier
- CFE0001076, ucf:46787
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001076
- Title
- NEW OPTIMAL HIGH EFFICIENCY DSP-BASED DIGITAL CONTROLLER DESIGN FOR SUPER HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MOTOR.
- Creator
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zhao, limei, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly...
Show moreThis dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly efficient digital controller. However, there are still challenges for such super high-speed controller design because of its stability, high-speed, variable speed operation, and required efficiency over a wide speed range. Currently, limited research, and no commercial experimental analysis, is available concerning such motors and their control system design. The stability of a super high-speed PMSM is an important issue particularly for open-loop control, given that PMSM are unstable after exceeding a certain applied frequency. In this dissertation, the stability of super high-speed PMSM is analyzed and some design suggestions are given to maximize this parameter. For ordinary motors, the V/f control curve is a straight line with a boost voltage because the stator resistance is negligible and only has a significant effect around the DC frequency. However, for the proposed super high-speed PMSM the situation is quite different because of the motor's size. The stator resistance is quite large compared with the stator reactive impedance and cannot be neglected when employing constant a V/f control method. The challenge is to design an optimal constant V/f control scheme to raise efficiency with constant V/f control. In the development, test systems and prototype boards were built and experimental results confirmed the effectiveness of the dissertation system.
Show less - Date Issued
- 2005
- Identifier
- CFE0000856, ucf:46651
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000856
- Title
- SOLUTION OF ELECTROMAGNETIC SCATTERING PARAMETERS AND RADIATION PATTERNS OF ARBITRARY BODY OF REVOLUTION RADIATORS.
- Creator
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Brokaw, Wendell, Wu, Thomas, University of Central Florida
- Abstract / Description
-
A novel full wave analysis method to determine the scattering parameters and the radiation field intensities of arbitrary Body of Revolution (BOR) radiators consisting of impenetrable media is explored through derived components of modal analysis and the method of moments (MoM). Modal excitation is utilized to excite the structural feed; allowing for a more accurate measure of the scattering parameters of the total structure as opposed to the use of external excitation sources. The derivation...
Show moreA novel full wave analysis method to determine the scattering parameters and the radiation field intensities of arbitrary Body of Revolution (BOR) radiators consisting of impenetrable media is explored through derived components of modal analysis and the method of moments (MoM). Modal excitation is utilized to excite the structural feed; allowing for a more accurate measure of the scattering parameters of the total structure as opposed to the use of external excitation sources. The derivation of the mode matching method introduces a novel approach to achieving a frequency independent coupling matrix that will reduce the computational requirements for iterations utilized in the solution of multi-step discontinuous junctions. An application of interpolation functions across a single element of the MoM's traditional basis function approach allows for the ability to facilitate the meshing of complex structures. The combined field integral equation method is implemented in the analysis method to assure the mitigation of spurious solutions that can be problematic for electric field integral equation solutions that are predominant in many MoM based codes. The structures of interest represent bodies of revolution (BOR), which maintains that the structures must exhibit rotational symmetry about the longitudinal, or directional, axis. The complexity of the domain of structures that can be treated with the analysis method will be significantly reduced through the use of BOR symmetry of the structure. The proposed method for the solution of structures will include the comprehensive treatment of Boundary Value Problems (BVP's) through modal analysis, aperture treatment, and an application of the method of moments. Solutions for BOR radiating structures can be divided into two regions of analytical concern, the inner guided wave region and the outer radiating region. Modal analysis will be used to determine the scattering matrix of the inner guided wave region. The modal analysis will consist of subdividing the inner region into a number of finite step discontinuities, and the method of mode matching will be implemented to numerically solve the BVP's at each step discontinuity for a finite number of modal field distributions. The surface field equivalence principle will be applied to treat the aperture in order to produce an equivalent problem that supplants a source magnetic current density and an induced electric current density across the aperture that will radiate in the presence of the outer structural material of the BOR radiator. An algorithm utilizing the MoM is applied to solve integral equations that are defined to treat the surfaces of the BOR structure using electromagnetic boundary conditions. The application of the MoM will develop the field intensities on the aperture with complete consideration of the outer structural boundaries of the BOR radiator. The field intensities on the aperture will be related to the inner guided wave region through electromagnetic boundary conditions, and an admittance matrix will be numerically calculated. The admittance matrix will then apply to the inner guided wave region's scattering matrix to determine the reflection and transmission coefficients at the input of the BOR radiator. The comprehensive solution method will be applied to a variety of BOR structures; the electromagnetic solutions of the structures as obtained by the proposed method shall be verified for accuracy against comparative analysis of the structures using known computational packages that have been generally accepted throughout industry with respect to design capabilities.
Show less - Date Issued
- 2005
- Identifier
- CFE0000747, ucf:46588
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000747
- Title
- PREDICTION AND MEASUREMENT OF RADIATED EMISSIONS BASED ON EMPIRICAL TIME DOMAIN CONDUCTED MEASUREMENTS.
- Creator
-
Freeman, Larry, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This thesis develops a novel method to predict radiated emissions measurements. The techniques used are based on standard Electromagnetic Compatibility (EMC) qualification test methods. The empirical data used to formulate the final results was restricted to pertinent data protocol waveforms however the entire method may be applied to any waveforms for which empirical radiated emissions have been measured. The method provides a concise means for predicting worst case radiated emissions...
Show moreThis thesis develops a novel method to predict radiated emissions measurements. The techniques used are based on standard Electromagnetic Compatibility (EMC) qualification test methods. The empirical data used to formulate the final results was restricted to pertinent data protocol waveforms however the entire method may be applied to any waveforms for which empirical radiated emissions have been measured. The method provides a concise means for predicting worst case radiated emissions profiles based on empirical measured data.
Show less - Date Issued
- 2006
- Identifier
- CFE0001294, ucf:46880
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001294
- Title
- NUMERICAL MODELING OF WAVE PROPAGATION IN NONLINEAR PHOTONIC CRYSTAL FIBER.
- Creator
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Khan, Md. Kaisar, Wu, Thomas, University of Central Florida
- Abstract / Description
-
In this dissertation, we propose numerical techniques to explain physical phenomenon of nonlinear photonic crystal fiber (PCF). We explain novel physical effects occurred in PCF subjected to very short duration pulses including soliton. To overcome the limitations in the analytical formulation for PCF, an accurate and efficient numerical analysis is required to explain both linear and nonlinear physical characteristics. A vector finite element based model was developed to precisely synthesize...
Show moreIn this dissertation, we propose numerical techniques to explain physical phenomenon of nonlinear photonic crystal fiber (PCF). We explain novel physical effects occurred in PCF subjected to very short duration pulses including soliton. To overcome the limitations in the analytical formulation for PCF, an accurate and efficient numerical analysis is required to explain both linear and nonlinear physical characteristics. A vector finite element based model was developed to precisely synthesize the guided modes in order to evaluate coupling coefficients, nonlinear coefficient and higher order dispersions of PCFs. This finite element model (FEM) is capable of evaluating coupling length of directional coupler implemented in dual core PCF, which was supported by existing experimental results. We used the parameters extracted from FEM in higher order coupled nonlinear Schrödinger equation (HCNLSE) to model short duration pulses including soliton propagation through the PCF. Split-step Fourier Method (SSFM) was used to solve HCNLSE. Recently, reported experimental work reveals that the dual core PCF behaves like a nonlinear switch and also it initiates continuum generation which could be used as a broadband source for wavelength division multiplexing (WDM). These physical effects could not be explained by the existing analytical formulae such as the one used for the regular fiber. In PCF the electromagnetic wave encounters periodic changes of material that demand a numerical solution in both linear and nonlinear domain for better accuracy. Our numerical approach is capable of explaining switching and some of the spectral features found in the experiment with much higher degree of design freedom. Numerical results can also be used to further guide experiments and theoretical modeling.
Show less - Date Issued
- 2008
- Identifier
- CFE0002248, ucf:47879
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002248
- Title
- A Fitness Function Elimination Theory for Blackbox Optimization and Problem Class Learning.
- Creator
-
Anil, Gautham, Wu, Annie, Wiegand, Rudolf, Stanley, Kenneth, Clarke, Thomas, Jansen, Thomas, University of Central Florida
- Abstract / Description
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The modern view of optimization is that optimization algorithms are not designed in a vacuum, but can make use of information regarding the broad class of objective functions from which a problem instance is drawn. Using this knowledge, we want to design optimization algorithms that execute quickly (efficiency), solve the objective function with minimal samples (performance), and are applicable over a wide range of problems (abstraction). However, we present a new theory for blackbox...
Show moreThe modern view of optimization is that optimization algorithms are not designed in a vacuum, but can make use of information regarding the broad class of objective functions from which a problem instance is drawn. Using this knowledge, we want to design optimization algorithms that execute quickly (efficiency), solve the objective function with minimal samples (performance), and are applicable over a wide range of problems (abstraction). However, we present a new theory for blackbox optimization from which, we conclude that of these three desired characteristics, only two can be maximized by any algorithm.We put forward an alternate view of optimization where we use knowledge about the problem class and samples from the problem instance to identify which problem instances from the class are being solved. From this Elimination of Fitness Functions approach, an idealized optimization algorithm that minimizes sample counts over any problem class, given complete knowledge about the class, is designed. This theory allows us to learn more about the difficulty of various problems, and we are able to use it to develop problem complexity bounds.We present general methods to model this algorithm over a particular problem class and gain efficiency at the cost of specifically targeting that class. This is demonstrated over the Generalized Leading-Ones problem and a generalization called LO**, and efficient algorithms with optimal performance are derived and analyzed. We also tighten existing bounds for LO***. Additionally, we present a probabilistic framework based on our Elimination of Fitness Functions approach that clarifies how one can ideally learn about the problem class we face from the objective functions. This problem learning increases the performance of an optimization algorithm at the cost of abstraction.In the context of this theory, we re-examine the blackbox framework as an algorithm design framework and suggest several improvements to existing methods, including incorporating problem learning, not being restricted to blackbox framework and building parametrized algorithms. We feel that this theory and our recommendations will help a practitioner make substantially better use of all that is available in typical practical optimization algorithm design scenarios.
Show less - Date Issued
- 2012
- Identifier
- CFE0004511, ucf:49268
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004511
- Title
- Self-heating control of edge emitting and vertical cavity surface emitting lasers.
- Creator
-
Zhang, Yu, Deppe, Dennis, Fathpour, Sasan, Likamwa, Patrick, Wu, Thomas, University of Central Florida
- Abstract / Description
-
Self-heating leads to temperature rise of laser diode and limits the output power, efficiency and modulation bandwidth due to increased loss and decreased differential gain. The main heat sources in laser diode during continuous wave operation are Joule heating and free carrier absorption loss. To control device self-heating, the epi structure needs to be designed with low electrical resistance and low absorption loss, while the heat flux must spread out of the device efficiently. This...
Show moreSelf-heating leads to temperature rise of laser diode and limits the output power, efficiency and modulation bandwidth due to increased loss and decreased differential gain. The main heat sources in laser diode during continuous wave operation are Joule heating and free carrier absorption loss. To control device self-heating, the epi structure needs to be designed with low electrical resistance and low absorption loss, while the heat flux must spread out of the device efficiently. This dissertation presents the control of self-heating of both edge emitting laser diodes and vertical cavity surface emitting lasers (VCSELs). For the 980nm high power edge emitting laser, asymmetric waveguide is used for low free carrier absorption loss. The waveguide and cladding materials are optimized for high injection efficiency. BeO heatsink is applied to spread the heat efficiently. Injection efficiency of 71% and internal loss of 0.3 cm-1 have been achieved. A total output power of 9.3 W is measured from 0.5cm long device at 14.5A injection current. To further reduce the internal loss, the development of 980nm quantum dot active region is studied. Threshold current density as low as 59A/cm2 is reached. For the VCSELs, oxide-free structure is used to solve the self-heating problem of oxide VCSELs. Removing the oxide layer and using AlAs in the DBRs leads to record low thermal resistance. Optimization of the DBRs leads to low resistance and low free carrier absorption. Power conversion efficiency higher than 50% is achieved. To further reduce device voltage and heat generation, the development of intracavity contacts devices is introduced.
Show less - Date Issued
- 2014
- Identifier
- CFE0005749, ucf:50076
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005749
- Title
- Transparent Oxide Semiconductor Gate based MOSFETs for Sensor Applications.
- Creator
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Saikumar, Ashwin Kumar, Sundaram, Kalpathy, Wu, Thomas, Kapoor, Vikram, University of Central Florida
- Abstract / Description
-
Starting from small scale laboratories to the highly sophisticated industrial facilities, monitoring and control forms the most integral part. In order to perform this continuous monitoring we require an interface, that would operate between the system and its processing conditions and in turn which facilitates us to act accordingly. This interface is called as a sensor. There are various types of sensors available which have wide range of functionality in various different fields.The use of...
Show moreStarting from small scale laboratories to the highly sophisticated industrial facilities, monitoring and control forms the most integral part. In order to perform this continuous monitoring we require an interface, that would operate between the system and its processing conditions and in turn which facilitates us to act accordingly. This interface is called as a sensor. There are various types of sensors available which have wide range of functionality in various different fields.The use of transparent conducting oxide (TCO) in the field of sensor applications has increasedand has been the subject of extensive research. Good electrical properties, good optical properties, wide band gap, portability, easy processing, and low cost has led to the extensive research on TCO for sensor applications.For this research purpose two specific types of sensor applications namely, light sensing and humidity sensing were considered. For this purpose, two sets of metal-oxide-semiconductor field effect transistors (MOSFET) with one set having transparent aluminum doped zinc oxide and the other having indium tin oxide respectively as their gate metal was fabricated. The MOSFETs werefabricated using a four level mask and tested.
Show less - Date Issued
- 2014
- Identifier
- CFE0005547, ucf:50297
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005547
- Title
- Modeling and fault detection in DC side of Photovoltaic Arrays.
- Creator
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Akram, Mohd, Lotfifard, Saeed, Mikhael, Wasfy, Wu, Thomas, University of Central Florida
- Abstract / Description
-
Fault detection in PV systems is a key factor in maintaining the integrity of any PV system. Faults in photovoltaic systems can cause irrevocable damages to the stability of the PV system and substantially decrease the power output generated from the array of PV modules. Among'st the various AC and DC faults in a PV system, the clearance of the AC side faults is achieved by conventional AC protection schemes,the DC side, however , there still exists certain faults which are difficult to...
Show moreFault detection in PV systems is a key factor in maintaining the integrity of any PV system. Faults in photovoltaic systems can cause irrevocable damages to the stability of the PV system and substantially decrease the power output generated from the array of PV modules. Among'st the various AC and DC faults in a PV system, the clearance of the AC side faults is achieved by conventional AC protection schemes,the DC side, however , there still exists certain faults which are difficult to detect and clear. This paper deals with the modeling, detection and classification of these types of DC faults. It is essential to be able to simulate the PV characteristics and faults through software. In this thesis a comprehensive literature survey of fault detection methods for DC side of a PV system is presented. The disparities in the techniques employed for fault detection are studied . A new method for modeling the PV systems information only from manufacturers datasheet using both the Normal Operating Cell temperature conditions (NOCT) and Standard Operating Test Conditions (STC) conditions is then proposed.The input parameters for modeling the system are Isc,Voc,Impp,Vmpp and the temperature coefficients of Isc and Voc for both STC and NOCT conditions. The model is able to analyze the variations of PV parameters such as ideality factor, Series resistance, thermal voltage and Band gap energy of the PV module with temperature. Finally a novel intelligent method based on Probabilistic Neural Network for fault detection and classification for PV farm with string inverter technology is proposed.
Show less - Date Issued
- 2014
- Identifier
- CFE0005293, ucf:50571
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005293
- Title
- BEAM-STEERABLE AND RECONFIGURABLE REFLECTARRAY ANTENNAS FOR HIGH GAIN SPACE APPLICATIONS.
- Creator
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Karnati, Kalyan, Gong, Xun, Wahid, Parveen, Jones, W Linwood, Wu, Thomas, Cho, Hyoung Jin, University of Central Florida
- Abstract / Description
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Reflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent...
Show moreReflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent advantages and drawbacks of the reflectarray are discussed.In chapter 2, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under normal and waveguide incidences. The developed theory is also utilized to understand the difference between the TEM and TE10 mode of excitation. Using this theory, effects of different physical parameters on reflection properties of unit cells are studied without the need of full-wave simulations. Detailed analysis is performed for Ka-band reflectarray unit cells and verified by full-wave simulations. In addition, an approach to extract the Q factors using full-wave simulations is also presented. Lastly, a detailed study on the effects of inter-element spacing is discussed.Q factor theory discussed in chapter 2 is extended to account for the varying incidence angles and polarizations in chapter 3 utilizing Floquet modes. Emphasis is laid on elements located on planes where extremities in performance tend to occur. The antenna element properties are assessed in terms of maximum reflection loss and slope of the reflection phase. A thorough analysis is performed at Ka band and the results obtained are verified using full-wave simulations. Reflection coefficients over a 749-element reflectarray aperture for a broadside radiation pattern are presented for a couple of cases and the effects of coupling conditions in conjunction with incidence angles are demonstrated. The presented theory provides explicit physical intuition and guidelines for efficient and accurate reflectarray design.In chapter 4, tunable reflectarray elements capacitively loaded with Barium Strontium Titanate (BST) thin film are shown. The effects of substrate thickness, operating frequency and deposition pressure are shown utilizing coupling conditions and the performance is optimized. To ensure minimum affects from biasing, optimized biasing schemes are discussed. The proposed unit cells are fabricated and measured, demonstrating the reconfigurability by varying the applied E-field. To demonstrate the concept, a 45 element array is also designed and fabricated. Using anechoic chamber measurements, far-field patterns are obtained and a beam scan up to 25o is shown on the E-plane.Overall, novel theoretical approaches to analyze the reflection properties of the reflectarray elements using Q factors are developed. The proposed theoretical models provide valuable physical insight utilizing coupling conditions and aid in efficient reflectarray design. In addition, for the first time a continuously tunable reflectarray operating at Ka-band is presented using BST technology. Due to monolithic integration, the technique can be extended to higher frequencies such as V-band and above.
Show less - Date Issued
- 2015
- Identifier
- CFE0006040, ucf:50963
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006040
- Title
- Effect of particles on evaporation of droplet containing particles.
- Creator
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Wei, Yan, Chen, Ruey-Hung, Deng, Weiwei, Putnam, Shawn, Wu, Thomas, University of Central Florida
- Abstract / Description
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The evaporation of droplet containing insoluble particles has grown into an active area of research due to the needs for nanofluids for applications in heat transfer, combustion, and manufacturing desired micro/nano particles in the pharmaceutical industry. The evaporation of droplets containing particles involves complicated multiphase heat and mass transport. The evaporation process consists of two stages: the first stage consists of evaporation until a shell of particle forms or when the...
Show moreThe evaporation of droplet containing insoluble particles has grown into an active area of research due to the needs for nanofluids for applications in heat transfer, combustion, and manufacturing desired micro/nano particles in the pharmaceutical industry. The evaporation of droplets containing particles involves complicated multiphase heat and mass transport. The evaporation process consists of two stages: the first stage consists of evaporation until a shell of particle forms or when the solid to liquid ratio is sufficiently large and the second stage, where the droplet size is commonly assumed to be unchanged. The dissertation investigates the evaporation kinetics in the first stage. An experimental setup based on electrodynamic balance (EDB) is built to allow the observation of evaporation of a free standing micro size droplet. Besides experimental design, a novel theoretical model is developed to first describe the morphological evolution process in the absence of internal convection. The model accounts for the effect of particles at the droplet surface on the diffusion of liquid vapor. The gradually increasing particle number at the droplet surface reduces the area for evaporation, leading to reduction in evaporation rate in the first drying stage, contrary to previous assumptions. The evaporation in the first stage is controlled by Pe (defined as the ratio of droplet evaporation rate to the particle diffusion rate) and particle properties such as wettability. For large values of Pe, the particles concentration is high near the droplet surface, leading to the change of evaporation rate. For small values of Pe, the effect of particles on the evaporation rate of droplet in the first drying stage is small because particles are allowed sufficient time to redistribute within the droplet. The model analysis also reveals that particle wettability is an important factor affecting the first drying stage. For hydrophilic particles, the contact angle of the particles at the droplet surface is small, leading to small change of evaporation in the first stage. For the hydrophobic particles that have large contact angles, the change of evaporation rate in the first drying stage is larger. The evaporation model that accounts for the internal convection is also used to describe the evaporation process. In this model, the evaporation behavior during the first stage is controlled by the particle mobility, initial particle concentration, and droplet recession/evaporation rate. For particles with high mobility, the particle distribution within the droplet tends to be smooth. The effect of convection flow on the particles distribution becomes stronger as particle mobility decreases. Once the particles mobility is decreased to a limit at which the surface particle density is only controlled by the internal flow and the evaporation process is independent of the particles mobility. For a given internal flow field and a specific particles mobility, the duration of the first stage and the final dry particle size are both controlled by the initial particle concentration. A smaller/larger initial particle concentration results in a longer/shorter first stage and smaller/larger dry particle.
Show less - Date Issued
- 2015
- Identifier
- CFE0005903, ucf:50856
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005903
- Title
- Optical Fibers for Space-Division Multiplexed Transmission and Networking.
- Creator
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Xia, Cen, Li, Guifang, Moharam, Jim, Abouraddy, Ayman, Christodoulides, Demetrios, Wu, Thomas, University of Central Florida
- Abstract / Description
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Single-mode fiber transmission can no longer satisfy exponentially growing capacity demand. Space-division multiplexing (SDM) appears to be the only way able to dramatically improve the transmission capacity, for which, novel optical fiber is one of the key technologies. Such fibers must possess the following characteristics: 1) high mode density per cross-sectional area and 2) low crosstalk or low modal differential group delay (DMGD) to reduce complexity of digital signal processing. In...
Show moreSingle-mode fiber transmission can no longer satisfy exponentially growing capacity demand. Space-division multiplexing (SDM) appears to be the only way able to dramatically improve the transmission capacity, for which, novel optical fiber is one of the key technologies. Such fibers must possess the following characteristics: 1) high mode density per cross-sectional area and 2) low crosstalk or low modal differential group delay (DMGD) to reduce complexity of digital signal processing. In this dissertation, we explore the design and characterization of three kinds of fibers for SDM: few-mode fiber (FMF), few-mode multi-core fiber (FM-MCF) and coupled multi-core fiber (CMCF) as well as their applications in transmission and networking.For the ultra-high density need of SDM, we have proposed the FMMCF. It combines advantages of both the FMF and MCF. The challenge is the inter-core crosstalk of the high-order modes. By applying a hole-assisted structure and careful fiber design, the LP11 crosstalk has been suppressed down to -40dB per km. This allows separate transmission on LP01 and LP11 modes without penalty. In fact, a robust SDM transmission up to 200Tb/s has been achieved using this fiber.To overcome distributed modal crosstalk in conjunction with DMGD, supermodes in CMCFs have been proposed. The properties of supermodes were investigated using the coupled-mode theory. The immediate benefits include high mode density and large effective area. In supermode structures, core-to-core coupling is exploited to reduce modal crosstalk or minimize DMGD. In addition, higher-order supermodes have been discovered in CMCFs with few-mode cores. We show that higher-order supermodes in different waveguide array configurations can be strongly affected by angle-dependent couplings, leading to different modal fields. Analytical solutions are provided for linear, rectangular and ring arrays. Higher-order modes have been observed for the first time using S2 imaging method.Finally, we introduce FMF to gigabit-capable passive optical networks (GPON). By replacing the conventional splitter with a photonic lantern, upstream combining loss can be eliminated. Low crosstalk has been achieved by a customized mode-selective photonic lantern carefully coupled to the FMF. We have demonstrated the first few-mode GPON system with error-free performance over 20-km 3-mode transmission using a commercial GPON system carrying live Ethernet traffic. We then scale the 3-mode GPON system to 5-mode, which resulted in a 4dB net gain in power budget in comparison with current commercial single-mode GPON systems.
Show less - Date Issued
- 2015
- Identifier
- CFE0005910, ucf:50827
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005910
- Title
- Method for Derivation and Synthesis of Electromagnetic Environmental Effects Requirement Limits for Achieving System Level Electromagnetic Compatibility.
- Creator
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Freeman, Larry, Wu, Thomas, Wahid, Parveen, Wei, Lei, Sundaram, Kalpathy, Chow, Louis, University of Central Florida
- Abstract / Description
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As humans endeavor to build large-scale complex systems, it will necessitate the integration of engineering practices and techniques to allocate many of the design aspects and responsibility across traditional boundaries. Many of today's large-scale complex systems, like commercial aircraft, satellite systems, and even automobiles use parts from all over the world. A recently completed airframe, largest commercial aircraft in the world, took nearly 30 years to build, required over 400...
Show moreAs humans endeavor to build large-scale complex systems, it will necessitate the integration of engineering practices and techniques to allocate many of the design aspects and responsibility across traditional boundaries. Many of today's large-scale complex systems, like commercial aircraft, satellite systems, and even automobiles use parts from all over the world. A recently completed airframe, largest commercial aircraft in the world, took nearly 30 years to build, required over 400 different suppliers from 20 different countries. These kinds of projects dictate a method for derivation and synthesis of electromagnetic environmental effects (E3) requirement limits for achieving system level electromagnetic compatibility (EMC).If a system level EMC design is an assemblage of compliant subsystems, then the subsystems should be an assemblage of compliant module and component designs. This requires tailoring the system level requirements through to module or component level designs. The method discussed is applicable to a variety of designs across varying levels of complexity and importantly implementable early in the design process. The method provides rationale for derivation of limits while maintaining traceability to system level requirements. Specific examples using the four common divisions of EMC requirements, conducted emissions, radiated emissions, conducted susceptibility, and radiated susceptibility are included. An overall system engineering approach and formal methodology is included. Detailed comparison examples using commercial and military EMC requirements are also included. Lastly, a discussion is included on comparison and margin analysis of input filtering for verifying compliance to requirements at the system level.
Show less - Date Issued
- 2016
- Identifier
- CFE0006303, ucf:51603
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006303
- Title
- Design of High-Efficiency Rare-Earth Permanent Magnet Synchronous Motor and Drive System.
- Creator
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Liu, Hanzhou, Wu, Thomas, Batarseh, Issa, Haralambous, Michael, Lin, Mingjie, Chow, Louis, University of Central Florida
- Abstract / Description
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Utilization of renewable energy has become the future trend in the trucking industry. Electrical power generated from renewable energy can replace part of the fuel usage. There is usually limited space for storing on-board battery. Thus, to better utilize the battery power, it becomes critical to have an efficient energy conversion device that can transfer energy from battery to amenities such as air conditioner, microwave, TV, mini refrigerator, etc. In this dissertation, a designed...
Show moreUtilization of renewable energy has become the future trend in the trucking industry. Electrical power generated from renewable energy can replace part of the fuel usage. There is usually limited space for storing on-board battery. Thus, to better utilize the battery power, it becomes critical to have an efficient energy conversion device that can transfer energy from battery to amenities such as air conditioner, microwave, TV, mini refrigerator, etc. In this dissertation, a designed permanent magnet synchronous motor (PMSM) can be such energy conversion device for an electric Auxiliary Power Unit (APU) application, which will have a desired output power of 2 kW at 2krpm, and maintain an efficiency greater than 90%. The design calls for good performance over a speed range of 1.5 krpm to 2.5 krpm. The current air conditioning system for automobile works only by (")on(") or (")off(") mode. For the heat mode, that means it is on with heat once the cabin temperature drops down to a level and off if the temperature rises back above that level. For the cool mode, that means it is on with cold air once the cabin temperature rises above a level, and off if the temperature drops back to that level. This is because the motor does not have the speed control functionality according to the temperature variation and people in the cabin do not feel much comfortable for that temperature change periodically as well as the inefficient energy consumption. With our novel technology, the designed motor can adjust its speed through the embedded system of our novel DC to AC inverter to provide a variable load. For example, with high efficiency, the fully charged battery sets (48 volts) can supply the electrical power and cooling to the cabin forabout 10 hours without recharging using the main engine.Copper loss is the most significant part of all the losses in low speed electric machines. Reducing the copper loss is the key to build highly efficient machine. We use copper wires with the current density lower than traditional design which result in large cross section of the wire and thus reduce the copper loss and improve the efficiency. This also makes thermal management easier and reduces the need to use active cooling methodologies (such as fan, liquid cooling or spray cooling); and hence the overall power density of the whole system (including cooling devices) will not decease much. In traditional machine design, the torque angle is designed to be in the rangeof 15 to 30 degrees at the rated power and speed. In our high efficiency motor design, we propose to use much lower torque angle of 2 to 15 degrees at the rated power and speed. Such design caneffectively increase the overload power handling capability and efficiency. Besides, small torque angle will result in large airgap size and increased thickness of the permanent magnets. Large airgap helps to reduce the windage loss of the machine and generates a lot less mechanical noise based on our design experience. Increased thickness of the permanent magnets helps to avoid thedemagnetization.As the technology of advanced micro-controller develops, fast response power electronic devices can be used in the motor controller. A novel design of DC to AC inverter with the fieldoriented control scheme and sliding mode observer algorithm for driving the designed motor is developed. The inverter has the capability of driving the motor with its output power at 2 kW.
Show less - Date Issued
- 2015
- Identifier
- CFE0006224, ucf:51064
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006224
