No description available.

Today's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided or minimized if a quiet building site is selected in the first place. Accelerometers and gauss meters combined with a computer for acquisition and analysis provide a low cost method of evaluating noise levels at proposed building sites. This work examines low frequency vibration and electromagnetic fields at two proposed sites for the planned Physical Science Building at the University of Central Florida.

The increasing market demand for wideband gap (WBG) power switches has led to heightened competition to increase converter power density, switching frequencies, and reduce form factor, among other factors. However, this technology has also brought about an increase in encounters with electromagnetic interference (EMI), posing significant challenges. Nevertheless, the maturation of power switches has been accompanied by an improvement in gate drive technology aimed at resolving EMI challenges, albeit at a higher component and cost expense. This thesis aims to design, analyze, and implement a recent innovative differential gate driver for a 1.2 kV SiC MOSFET full bridge module. The purpose of this design is to mitigate EMI, improve performance, and reduce the number of filtering elements that are typically required. The investigation into the impact of EMI on electrical systems involves exploring factors such as testing equipment, power supplies, and gate drive layout. Based on these considerations, system and sub-system level analyses are conducted to derive practical design recommendations for implementing the differential gate driver. Three gate drive PCBs are designed and evaluated through extensive double pulse tests (DPTs). Furthermore, continuous switching of the driver presents its own set of challenges that are not apparent during the DPTs, requiring further exploration of low-cost solutions. Finally, a comparison between custom and discrete module solutions employing 1.2 kV SiC MOSFETs is conducted, highlighting the advantages and disadvantages of each approach. The solutions proposed in this work are intended to be extended to other gate drive ICs, with the goal of providing valuable insights and guidelines for EMI suppression and gate driver performance enhancement. / Master of Science / The increasing demand for powerful and efficient electronic devices has led to competition to develop better converters with wideband gap (WBG) power switches. These switches can make electronics work faster and take up less space, but they can also cause electromagnetic interference (EMI) that can be problematic. Despite these challenges, advances in power switch technology have led to improvements in gate drive technology, which can help reduce EMI, albeit, sometimes, at a higher cost. This research aims to design and analyze an innovative differential gate driver for a 1.2 kV SiC MOSFET full bridge module that can help mitigate EMI, improve performance, and reduce the number of required filtering elements. A system-level analysis is conducted to identify critical noise paths and potential solutions in response to poor gate driver performance. Practical design recommendations are provided for implementing a differential gate driver, and three PCB designs are tested and evaluated to showcase the effectiveness of the proposed solutions. The work also includes a comparison between a custom module and discrete module solutions employing 1.2 kV SiC MOSFETs, highlighting the advantages and disadvantages of each approach. The findings are extended to other gate drivers that share similar performance specifications, demonstrating the potential and improvements that can be achieved with the suggested techniques. Overall, the study provides valuable insights and guidelines for EMI suppression and performance enhancement in power electronics systems utilizing differential gate drivers.

Electrical methods of geophysical survey are known to produce results that are hard to predict at different times of the year, and under differing weather conditions. This is a problem which can lead to misinterpretation of archaeological features under investigation. The dynamic relationship between a ‘natural’ soil matrix and an archaeological feature is a complex one, which greatly affects the success of the feature’s detection when using active electrical methods of geophysical survey. This study has monitored the gradual variation of measured resistivity over a selection of study areas. By targeting difficult to find, and often ‘missing’ electrical anomalies of known archaeological features, this study has increased the understanding of both the detection and interpretation capabilities of such geophysical surveys. A 16 month time-lapse study over 4 archaeological features has taken place to investigate the aforementioned detection problem across different soils and environments. In addition to the commonly used Twin-Probe earth resistance survey, electrical resistivity imaging (ERI) and quadrature electro-magnetic induction (EMI) were also utilised to explore the problem. Statistical analyses have provided a novel interpretation, which has yielded new insights into how the detection of archaeological features is influenced by the relationship between the target feature and the surrounding ‘natural’ soils. The study has highlighted both the complexity and previous misconceptions around the predictability of the electrical methods. The analysis has confirmed that each site provides an individual and nuanced situation, the variation clearly relating to the composition of the soils (particularly pore size) and the local weather history. The wide range of reasons behind survey success at each specific study site has been revealed. The outcomes have shown that a simplistic model of seasonality is not universally applicable to the electrical detection of archaeological features. This has led to the development of a method for quantifying survey success, enabling a deeper understanding of the unique way in which each site is affected by the interaction of local environmental and geological conditions.

No description available.

With the development and use of Silicon-Carbide [Silicon-Carbide (SiC)] devices come a host of advantages, including higher switching frequency, improved thermal performance, and higher voltage rating. This higher switching frequency can reduce the size of the con- verter system, but is typically associated with higher dv/dt voltage slew rates that further increase electromagnetic interference (EMI) related phenomena. Conventional gate-drivers are very limited in the way that they can control this high dv/dt, and this leads to the use of active gate-drivers. This thesis will explore the use of an active voltage-controlled gate-driver for SiC devices, utilizing transiently a voltage closer to the Miller plateau than the nominal turn-on and turn-off voltage to introduce control over the switching transient. Various ap- plied voltages, and voltage sequences will be evaluated to determine their effectiveness for controlling dv/dt and their impact on switching loss. Through this work, a better under- standing of the advantages and drawbacks of an active gate-driver can be found. The main result from this work is the effective reduction in the dv/dt generated by MOSFET devices, which was attained at a lower switching loss penalty compared to conventional resistive gate-drivers operating at similar dv/dt rates. Simulation and experimental results obtained with a prototype active gate-driver circuitry were used for this evaluation. / Master of Science / Within power electronic systems such as an inverter used to connect solar panels to the grid, are electrically controlled switches. These switches traditionally have been made of Silicon (Si) which imposed limitations on how fast they could transition from off to on, and vice versa, they also could only switch a relatively small number of times per second. However, a new generation of devices made from a silicon carbide material are being increasingly adopted, some key advantages of these new devices include much higher number of times to switch per second, and faster transitions from off-on and on-off. The trade-off that comes with this faster operation is an increase in the electromagnetic noise generated by these switches, among other issues. This work looks to explore a more unique method of controlling the turn-on and turn-off of these new switches and evaluating its impact on the noise generated and the losses during switching.

Switch mode power supplies are widely used in different applications. High efficiency and high power density are two driving forces for power supply systems. However, high dv/dt and di/dt in switch mode power supplies will cause severe EMI noise issue. In a typical front-end converter, the EMI filter usually occupies 1/3 to 1/4 volume of total converter. Hence, reducing the EMI noise of power converter can help reduce the volume of EMI filter and improving the total power density of the converter. For off-line switch mode power supplies, DM noise is dominated by PFC converter. CM noise is a more complicated issue. It is contributed by both PFC converter and DC/DC converter. While many researches have focused on reducing CM noise for PFC converter, the CM noise of DC/DC converter still remains a challenge. The main objective of this thesis is provide a solution to have best CM noise reduction for DC/DC converters. The shielding concept and balance concept are combined to propose a novel balance double shielding technique. This method can have an effective CM noise reduction in the circuit level. In addition it is easy to design and implement in the real production. The balance condition is easily controlled and guarantees effective CM noise reduction in mass production. Then, a novel one-layer shielding method for PCB winding transformer is provided. This shielding technique can block CM noise from primary side and also cancel the CM noise from secondary side. In addition, shielding does not increase the loss of converter too much. Furthermore, this shielding technique can be applied to matrix transformer structure. For matrix transformer LLC converter, the inter-winding capacitor is very large and will cause severe CM noise problem. By adding shielding layer, CM noise has been greatly reduced. In addition, by modifying the secondary winding, the loss on shielding layer is minimized and experiments show that the total efficiency of converter has almost no impact. Furthermore, although this thesis uses flyback and LLC resonant converter as example to demonstrate the concept, the novel shielding technique can also be applied to other topologies that have similar transformer structure. / Master of Science

It is well known that common-mode (CM) conducted electromagnetic interference (EMI) is caused by the common-mode current flowing through the parasitic capacitance of transistors, diodes, and transformers to ground in the power circuit. Because of the potential for interference with other systems as well as governmental regulations, it is necessary to attenuate this noise. Ordinarily this must be accomplished by using a magnetic choke on the input power lines, which can result in large penalties to the overall size, weight, and cost of the completed system. In order to lessen the requirement for this magnetic choke, there has been in recent years a desire to introduce noise cancellation techniques to the area of EMI. This text introduces a method of canceling the common-mode EMI by using a compensating transformer winding and a capacitor. Compared with active cancellation techniques, it is much simpler and requires no additional transistors and gate-drive circuitry since it merely adds a small copper winding and a small capacitor. By using this technique the size of the EMI filter can be reduced, especially for applications requiring high currents. In this thesis a survey of CM noise reduction techniques is presented, encompassing conventional and active cancellation techniques. The new method for passive noise cancellation is presented, which is then applied to families of isolated DC/DC converters, non-isolated DC/DC converters, and DC/AC inverters and motor drives. The method, results, and ramifications of this technique are presented in order of appearance. / Master of Science

Switch mode power supplies are widely used in different applications. High efficiency and high power density are two driving forces for power supply systems. However, high dv/dt and di/dt in switch mode power supplies will cause severe EMI noise issue. In a typical front-end converter, the EMI filter usually occupies 1/3 to 1/4 volume of total converter. Hence, reducing the EMI noise of power converter can help reduce the volume of EMI filter and improving the total power density of the converter. The EMI noise can be separated as differential mode (DM) noise and common mode (CM) noise. For off-line switch mode power supplies, DM noise is dominated by PFC converter. CM noise is a more complicated issue. It is contributed by both PFC converter and DC/DC converter. The DM noise is contributed by input current ripple. Therefore, one method to reduce DM noise is interleaving. There are three methods to reduce CM noise: symmetry, balance and shielding. The idea of symmetry concept is generating another dv/dt source to cancel the original dv/dt source. However, this method is very difficult to achieve and usually has more loss. The balance technique forms a Wheatstone bridge circuit to minimize the CM noise. However, the balance technique cannot achieve very good attenuation at high frequency due to parasitics. Shielding technique is very popular in isolated DC-DC converters to reduce CM noise. However, the previous shielding method requires precise control of parasitic capacitance and dv/dt. It is very difficult to achieve good CM noise attenuation in mass production. In this dissertation, a novel one-layer shielding method for PCB winding transformer is provided. This shielding technique can block CM noise from primary side and also cancel the CM noise from secondary side. In addition, shielding does not increase the loss of converter too much. Furthermore, this shielding technique can be applied to matrix transformer structure. For matrix transformer LLC converter, the inter-winding capacitor is very large and will cause severe CM noise problem. By adding shielding layer, CM noise has been greatly reduced. Although flyback and LLC resonant converter are used as examples to demonstrate the concept, the novel shielding technique can also be applied to other topologies that have similar transformer structure. With Wide-band-gap power devices, the switching frequency of power converter can be pushed 10 times higher than traditional Si based converters. This provides an opportunity to use PCB winding magnetics. In order to reduce the switching loss, critical conduction mode is used in PFC converter. Because of high AC current in the inductor winding, litz wire was used to build the inductor. However, with coupled inductor concept and the proposed winding structure, CRM inductor is integrate into PCB winding for the first time. Furthermore, balance technique is applied to reduce CM noise for PFC converter. With PCB winding, the balance technique has better high frequency performance. The PCB winding inductor can achieve high power density, high efficiency and automated manufacture. Traditionally, two-stage EMI filter was utilized to achieve required EMI noise attenuation. With the developed high frequency, low EMI noise converter, single-stage EMI filter can be applied. However, there are self-parasitic and mutual parasitic components to impact the filter performance on high frequency. The near-field measurement is utilized to visualize the magnetic flux near those filter components. Thus, a better filter design and layout can be achieved to have better high frequency performance. / Ph. D. / Switch mode power supplies are widely used in different applications. High efficiency and high power density are two driving forces for power supply systems. In a world full of electronic devices, it is very important that these devices can work properly in a complicated electromagnetic environment. Thus, electromagnetic compatibility (EMC) is a significant characteristic of electronic devices. However, high dv/dt and di/dt in switch mode power supplies will cause severe EMI noise issue. In a typical front-end converter, the EMI filter usually occupies 1/3 to 1/4 volume of total converter. Hence, reducing the EMI noise of power converter can help reduce the volume of EMI filter and improving the total power density of the converter. In this dissertation, several methods to reduce EMI noise are proposed and analyzed. First, the shielding method for PCB winding transformer is proposed. It can effectively reduce EMI noise at wide frequency range. Second, balance technique is applied to reduce EMI noise of PFC converter. Traditionally, two-stage EMI filter was utilized to achieve required EMI noise attenuation. With the developed high frequency, low EMI noise converter, single-stage EMI filter can be applied. However, there are self-parasitic and mutual parasitic components to impact the filter performance on high frequency. The near-field measurement is utilized to visualize the magnetic flux near those filter components. Thus, a better filter design and layout can be achieved to have better high frequency performance.

The average life expectancy and the proportion of elderly are increasing globally and inSweden, causing challenges for the society. Physical activity has proven to bring a number ofpositive benefits in older people, making the promotion of physical activity an important partof healthy aging attempts. The degree of physical activity in Sweden’s elderly population isgreater than in previous generations, making this group a positive exception from a widerperspective. A cross sectional study was made in order to investigate which motives tophysical activity that was considered most important among people above 60. Collected datawere analyzed with SPSS version 19.0 and the result showed that most of the given motiveswere viewed as important. Avoiding sickness and bad health and motives related toimprovement and maintaining of physical fitness were given the highest values. The degree ofphysical activity among the participants were also collected and a bivariate analyze could thusbe performed to investigate possible relations between physical activity and differentmotives. A statistic significant relation between a high degree of physical activity at gym(more than 2 days a week) and a high valuation of motives related the social aspect, goodfeelings and self-development were then found. / Medellivslängden och andelen äldre ökar i världen och i Sverige vilket kommer innebärastora utmaningar. Fysisk aktivitet har flertalet goda effekter för äldre människor och attfrämja fysiskt aktivitet blir en således en viktig del i arbetet med att åstadkomma etthälsosamt åldrande. Positivt är då att Sveriges äldre befolkning är fysiskt aktiva i högre gradän tidigare generationer. Därför genomfördes en tvärsnittsstudie med syfte att undersökavilka motiv till fysisk aktivitet som ansågs ha störst betydelse för fysiskt aktiva människoröver 60 år. Data analyserades i SPSS version 19.0 och resultatet visade att flertalet av 21angivna motiv hade stor betydelse för de äldres fysiska aktivitet. Att undvika sjukdom ochhälsobesvär samt att bevara/förbättra aspekter av den fysiska formen ansågs dock viktigast.Deltagarna fick också ange i vilken grad de var fysiskt aktiva och således kunde sambandmellan olika motiv och fysisk aktivitet beräknas. Ett fåtal statistiskt signifikanta sambandhittades då det visade sig att personer som värderade den sociala biten, de goda känslornaoch självutveckling högst var fysiskt aktiva på gym i högre grad (över 2 dagar i veckan) än desom gav dessa motiv lägre värden.