Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 27, 2009) Includes bibliographical references.

Thesis (M.S.)--Ohio University, November, 2004. / Title from PDF t.p. Includes bibliographical references (p. 76-77)

M.Ing. (Electrical And Electronic Engineering) / In this dissertation, an investigation into reducing Electromagnetic Interference (EMI) through design is presented. Root generation mechanisms of Electromagnetic Interference are often neglected during the design process and later treated symptomatically. Mitigation of Electromagnetic Interference at source often reduces cost and physical size of electronics. This dissertation demonstrates the process and results by which schematic balance mitigates EMI. In addition, the introduction of Geometric Balance and physically designing circuits to be Geometrically Symmetrical are presented and tested to determine whether the design produces mitigating EMI results. Multiple Printed Circuit Boards (PCB’s) were developed and tested against each other to demonstrate schematic balance and other EMI generation mechanisms. The final PCB was designed to be Geometrically Symmetrical and the test results compared. The results illustrate the varying performance of each PCB due to their differing design. The Geometrically Symmetrical PCB presented the best results due to various improvements which include physical layout size and semiconductor placement. An additional important phenomenon discovered was the amount of EMI generated during MOSFET Driver operation. This contributed to a significant amount of EMI during the no-load phase of testing.

M.Ing. / In power electronics most applications are custom designed. Even though similar topologies are used, each application is designed to fit specific requirements. Presently there is a move towards standard modules that can be connected together to perform the desired power conversion, in much the same way as IC’s have been used for a few decades now. It is important to ensure that the modules can work together without performance degradation. The close proximity of active, passive and logic devices in high power applications dramatically increases the risk of EMI between the various components. This document describes the design and characterisation of a planar conducted RF-EMI power line filter to be used between modules and between modules and power supplies. The filter consists of two sets of transmission lines in parallel. The first is a high permittivity material with nickel conductors, referred to as the attenuator. The second is a set of copper conductors that are placed on the outside of the attenuator. The filter must be able to remove conducted differential mode noise from power line to the module and from the module tot the power line. The filter dimensions are comparable to the wavelengths that have to be attenuated. This allows for a possible combination of RF filtering techniques and power line filtering techniques. The design of the filter and the electromagnetic effects that govern its behaviour is explained. The transfer characteristic of the filter is made possible by the choice of materials and their relation to each other. Each material is discussed and evaluated. Characterisation methods are described and results presented. The influence the materials have on the performance of the filter and the methods and problems of construction of the filter are discussed. The construction of the filter and the commercial processes available are discussed. A prototype filter was built to demonstrate the feasibility of the construction processes. The performance of the prototype filter was then measured. The various test set-ups for different applications are explained. Small signal tests in 50 W systems were used to allow for comparisons with other filter types. The prototype has minimal insertion loss in the pass band and an average slope of attenuation of 40 dB/decade beyond the corner frequency. The corner frequency is at 1 MHz. Transmission line theory is used to develop a distributed element model for the filter using the ABCD-matrix representation of transmission lines. From this matrix an equivalent P-model can be calculated. Applicable assumptions are made to simplify the equations and values for a lumped element P-model is calculated. Both models indicate the importance that the material parameters have on the performance of the simulation results. Good correlation between the measured performance and simulated performance is established. The material parameters are sensitive to temperature. A one-dimensional thermal model is presented to estimate the operating temperature of the filter. It is determined that the attenuation of the filter is primarily determined by the attenuator. Based on the findings, new attenuator designs are made in an attempt to improve the performance of the filter. The small signal measurements of the various designs and the test results under load conditions are compared. A power test is performed. The filter performance varies as the voltage rating is increased. Finally, a temperature characterisation is done. The filter is absorptive and heat is dissipated in both the conductors and the dielectric material. The filter performance is sensitive to the operating temperature. A summary of the technology and the evaluation of this type of filter are presented in the conclusion.

M.Ing. (Electrical & Electronic Engineering Science) / This study investigates the mitigation of conducted electromagnetic interference (EMI) in a flyback DC-DC converter. Without the use of filters, the maximum mitigation of EMI possible without significantly decreasing converter operating efficiency is investigated. The following parameters are found to influence EMI: · Switching speed: Decreasing switching speed (increasing rise and fall times of the MOSFET) effectively reduces both common mode (CM) and differential mode (DM) EMI above a certain frequency. Series gate resistors up to a certain value were found to not increase power dissipated in the MOSFET. Series gate resistors greater than this value, further reduce CM and DM EMI at the cost of larger amounts of power being dissipated in the MOSFET. · Leakage inductance and inter-winding capacitance: The dominant component of the flyback coupled inductor in terms of EMI generation is the inter-winding capacitance. Increasing inter-winding capacitance increases both CM and DM EMI. Reducing inter-winding capacitance increases leakage inductance. Increasing leakage inductance however, results in reduced converter efficiency. Coupled inductor design is therefore a compromise between leakage inductance and inter-winding capacitance. · Layout inductance: Reducing layout inductance in certain parts of the circuit is an effective method for reducing DM EMI. This is shown to also decrease CM EMI but not to the same extent as DM EMI. · Snubbing: Snubbing is shown to effectively reduce both CM and DM EMI by reducing the magnitude of the voltage overshoot and ringing on the drain of the MOSFET. Snubbing however reduces converter efficiency. This study gives important guidelines to the engineering trade-offs in reducing EMI versus efficiency in a flyback converter.

Master of Science / Department of Electrical and Computer Engineering / William B. Kuhn / Crosstalk and electromagnetic interference (EMI) are constant problems in the design of RF circuits. There have been several studies to analyze and improve isolation of transmission lines, but the focus has been mainly on digital circuits or the isolation goals have been on the order of 40-60 dB. When the isolation goals are much more stringent, such as 80-100 dB, much of a designer’s time is still spent ensuring that a circuit meets isolation and EMI constraints. This typically involves the use of extensive metal shielding over a circuit board. This thesis presents results from an isolation and EMI study to provide a simple reference that can be applied to typical substrates, provided proper scaling is used between substrates. The results in this thesis are reported from DC to 30 GHz using a low cost 4-layer FR4 process. The changes in isolation between various transmission lines types are investigated while varying line separation and length. It is shown that isolation between ground-backed coplanar waveguide (GBCPW) and stripline traces can reach 100dB through L-band and 60dB through Ku-band for 1.3in traces separated by 150mils. Due to the heavy usage of filters in RF design, the isolation between edge-coupled bandpass filters is also studied. It is seen that isolation levels of 100dB through L-band by enclosing the filters within stripline technology is possible, provided that signal launches and layer transitions are carefully designed. Within the passband of the 20 GHz filter tested, the isolation is less but is still significantly improved by use of enclosed stripline. Lastly, a preliminary assessment of EMI is presented which focuses on radiation levels as well as variables that can degrade isolation performance. The data illustrated in this thesis can provide guidance in the early stages of RF circuit design to determine appropriate structures to meet given design requirements. It also helps to assess the degree to which additional metal shielding can be avoided in PC board systems that use multi-layer technologies.

The South African railway company makes use of a train wheel detection system to monitor the trains present on a particular track, noting their lengths, positions and speeds. Interference due to distorted traction currents cause havoc with this system rendering the information gathered unreliable. To combat this interference two paths are available to reduce the detection systems susceptibility. These paths include the addition of shielding between the railway track and the wheel detectors, which form the functional entities of the train wheel detection system, and the installation of a cable running parallel to the railway track with connections to it some distance before and after the position of the wheel detector. To verify these paths, high frequency experiments were performed in the lab as well as FEM simulations. To perform the high frequency experiments a source capable of producing the high frequency current needed was designed and constructed, along with a well shielded measurement system to enable the mapping of the flux density within the region occupied by and surrounding the wheel detector. The results of both the experimental measurements and simulations yielded that the interfering magnetic field could indeed be reduced through the use of the two available paths, when they are both applied separately and in combination. To obtain the greater reduction in the interfering field within the area occupied by and surrounding the wheel detector the paths should be used in combination. Therefore through the use of a shield that is constructed from a magnetic material and the installation of a parallel cable the train wheel detection system can be made more robust. / Prof. W.A Cronjé Prof. I.W. Hofsajer

One of the difficulties in solving E:MI problems is the lack of diagnostic tools available. In this thesis work, a tool, called Noise Separator, is developed, which can be used to decipher the differential-mode (DM) noise and the common-mode (CM) noise from the total noise. A noise separator hardware is built and tested. The results show that at least 50 dB rejection to either DM or CM noise is achieved for frequency ranging from 10 KHz to 30 MHz. With the aid of the Noise Separator, EMI filter design is made easier. / Master of Science

Common mode (CM) electromagnetic interference (EMI) can compromise electronics systems, interfere with communication systems, and degrade mechanical systems. Multiple inverters can also generate excessive CM EMI that often exceeds individual inverter EMI standards. Due to their weight, volume, cost, and suboptimal performance, active and passive filters and chokes are inefficient as EMI mitigation options. By utilizing frequency modulation (FM) or spread spectrum frequency modulation (SSFM), EMI energy is dispersed. In spite of not requiring expensive, bulky, and heavy filters, these techniques produce significant ripples in output voltages and currents. This dissertation uses enhanced sinusoidal frequency modulation to reduce CM EMI output, bridging the gap between existing EMI solutions: 1) To reduce performance degradation, a state-of-the-art FM topology with duty cycle correction is proposed. Due to large output voltage and current ripples, FM techniques have limited bandwidth and utilization. Duty cycle correction allows for a wider FM bandwidth with better EMI attenuation while minimizing output ripple performance tradeoffs. 2) CM EMI accumulation is a growing concern in power converter networks. Even if each converter complies with EMI regulations, multiple converters may produce CM EMI that exceeds EMI standards in parallel operation. A novel algorithm is proposed to suppress CM EMI in a large-scale network using SFMCW frequency indexing. The algorithm minimizes aggregate EMI by minimizing switching frequency overlap among converters. 3) CM EMI noise in complex systems presents a critical challenge. Since standalone converters are rarely affected by CM EMI phases, they were usually overlooked in most studies until recently. CM currents generated by multiple converters can be added or subtracted based on phase differences. The CM currents in large systems with multiple inverters are distributed randomly, resulting in multiple peaks and nulls. In order to reduce network EMI, a sinusoidal FM technique with phase shift is proposed to attenuate CM EMI on multiple parallel inverters. This method overcomes conventional methods' critical disadvantages, including the need for accurate component characterization and modeling, and reducing CM EMI without additional passive components.

Electromagnetic compatibility (EMC) has become increasingly important in present electronic design. Modern high-speed circuitry has earned amplified attention from engineers due to its ability to interfere with neighboring circuitry through electromagnetic interference (EMI). As the operating speed and layout complexity of electronic circuit systems continues to increase, electromagnetic interference (EMI) becomes a serious issue facing circuit designers of the present and future. In this paper, the radiated emissions of a small PCB (including a microprocessor, SRAM, and flash memory) placed within a 1-GHz Crawford TEM (transverse electromagnetic) cell are analyzed. Various programs are executed while the microprocessor runs at different clock speeds. The dissimilarities in the radiated emission spectrums provided by the DUT (device under test) while running various programs at different clock speeds are compared and analyzed. All five programs run by the microprocessor show similar effects when the clock speed is varied. It is demonstrated that when the clock rate of the microprocessor increases, the overall radiation from the system increases. However, varying the software executed by the microprocessor is found to have effects on the emitted radiation pattern. The greatest noise within the radiated emission spectrum is found to come from programs in which the microprocessor communicates with the external SRAM chip. It is also found that the radiation levels for each program executed by the microprocessor change differently as the position of the microprocessor inside the TEM cell is varied. The fast paced lifestyle of modern society has undeniably led to an increase in desire for higher functionality of electronic devices. Whether it is a wireless device, a portable computer, or simply more electronic components inside an automobile, the need for electronics with more capabilities has become a standard in electronic design. However, to increase the function of a digital device, clock frequencies and software have to be altered. It is hoped that this paper will help engineers to take into consideration how changes in clock frequencies and software can affect the radiated EMI within their designs. An engineer's consideration of the effects of EMI within his/her design will help lead to safer, more reliable devices.