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.

Galvanic isolation between the grid and energy storage unit is typically required for bidirectional power distribution systems. Due to the recent advancement in wide-bandgap semiconductor devices, it has become feasible to achieve the galvanic isolation using bidirectional isolated DC/DC converters instead of line-frequency transformers. A survey of the latest generation SiC MOSFET is performed. The devices were compared against each other based on their key parameters. It was determined that under the given specifications, the most suitable devices are X3M0016120K 1.2 kV 16 mohm and C3M0010090K 900 V 10 mohm SiC MOSFETs from Wolfspeed. Two of the most commonly utilized bidirectional isolated DC/DC converter topologies, dual active bridge and CLLC resonant converter are introduced. The operating principle of these converter topologies are explained. A comparative analysis between the two converter topologies, focusing on total device loss, has been performed. It was found that the CLLC converter has lower total device loss compared to the dual active bridge converter under the given specifications. Loss analysis for the isolation transformer in the CLLC resonant converter was also performed at different switching frequencies. It was determined that the total converter loss was lowest at a switching frequency of 250 kHz A prototype for the CLLC resonant converter switching at 250 kHz was then designed and built. Bidirectional power delivery for the converter was verified for power levels up to 25 kW. The converter waveforms and efficiency data were captured at different power levels. Under forward mode operation, a peak efficiency of 98.3% at 15 kW was recorded, along with a full load efficiency value of 98.1% at 25 kW. Under reverse mode operation, a peak efficiency of 98.8% was measured at 17.8 kW. The full load efficiency at 25 kW under reverse mode operation is 98.5%. / Master of Science / Electrical isolation between the grid and energy storage unit is typically required for bidirectional power distribution systems. Traditionally, this isolation is achieved via line-frequency transformers, which tend to be bulky and heavy. This imposes a limit on the overall system power density, which is a crucial performance metric for bidirectional power distribution systems. Alternatively, the required electrical isolation can be implemented through bidirectional power converters. As a result, the overall system power density can be drastically improved. However, the losses incurred by the semiconductor devices in such converters could significantly reduce the overall system efficiency, which is another important performance metric. Due to the recent advancement in semiconductor devices, it has become feasible to design the required bidirectional power converters with high efficiency and high power density. A survey of the latest generation semiconductor devices is performed. A 25 kW converter prototype was designed and built using the selected semiconductor devices. Experimental testing was conducted for the converter prototype and efficiency values exceeding 98% were captured across the entire load range. The converter prototype has a power density of 78 W/in³.

In this thesis, the investigation focuses on the analysis of the high frequency characteristics and the nonlinearity of the transistors. In view of the III-V semiconductors which have excellent high frequency performance and the advantage for high frequency circuit design, the 0.15£gm InGaAs based pseudomorphic high electron mobility transistors provided by WIN semiconductor Corp. were used in this study. The high frequency measurement was utilized to extract both extrinsic and intrinsic components of the transistors, and further to establish the small signal equivalent model in each bias condition. According to the physical definition of the extracted gm, gds and the relationship with the output current, RF I-V curves could be determined through the integration procedure. The nonlinearity of the transistors can be attributed to the nonlinear input capacitance Cgs and Cgd, and the voltage dependent current source. The high frequency nonlinear models proposed in this thesis were based on classic Angelov model. For the high frequency application, the frequency dependent characteristics of the nonlinear sources would be taken into consideration through the combination of the RF I-V curves and extracted intrinsic components. Thus, the nonlinearities could be able to describe by nonlinear function through the fitting process and model the output performance completely. The accuracy of the models could be confirmed through the comparison between the simulation and the measurement result. Obviously, the high frequency models which include the high frequency effect and the nonlinear characteristics have excellent agreement with the experimental data.

Current technology used to diagnose hearing disorders is limited. This is mostly due to the fact that the auditory structures are very small and not easily accessible with existing imaging technologies. The objective of this dissertation was to investigate the potential of high-frequency ultrasound as a tool for exploring the anatomy of the auditory system. Three studies were conducted in order to demonstrate the feasibility of high-frequency ultrasound as a diagnostic technology for hearing disorders. In the first study, an in-house developed 50 MHz annular array-based ultrasound system was used to provide ex-vivo images of auditory structures in cadaveric temporal bones. It was shown that the spatial resolution was sufficient to visualize a high level of detail of the ossicular bones of the middle ear as well as intra-cochlear structures of the inner ear. In the second study, a 50 MHz 1.26? pitch phased array ultrasound transducer was designed for imaging intra-cochlear structures through the round window membrane. As this element pitch results in large grating lobe artifacts, novel transmit beamforming techniques were developed to suppress grating lobes resulting from this large-pitch array. Theoretical techniques using the impulse-response simulation method and experimental verification using high-frequency linear array ultrasound system (Vevo 2100, VisualSonics, Canada) showed that these techniques were able to suppress grating lobe levels up to 40 dB. In the third study, a needle mounted 45 MHz single-element ultrasound probe was fabricated in order to measure the vibrations of intra-cochlear structures on human cadavers. Basilar membrane velocimetry measurements were successfully performed using pulsed-wave Doppler ultrasound in the frequency range between 100 Hz-2 KHz. The measured velocity of the basilar membrane and the round window membrane showed that the middle ear resonance frequency near 1 KHz was present over multiple temporal bones. This is the first work that has explored the human auditory system with high resolution ultrasonic visualization and Doppler velocimetry.

Tato práce se zabývá automatickou detekcí vysokofrekvenčních oscilací jakožto moderního elektrofyziologického biomarkru epileptogenní tkáně v intrakraniálním EEG, jehož vizuální detekce je zdlouhavý proces, který je ovlivněn subjektivitou hodnotitele. Epilepsie je jedním z nejčastějších neurologických onemocnění postihující 1 % obyvatelstva. Přestože jsou přibližně dvě třetiny případů léčitelné farmakologicky, zbylá třetina pacientů je odkázána zejména na léčbu chirurgickým zákrokem, pro nějž je zapotřebí přesně lokalizovat ložisko patologické tkáně. Vysokofrekvenční oscilace jsou v posledním desetiletí studovány pro jejich potenciál lokalizace patologické tkáně. Součástí této práce je shrnutí dosavadního výzkumu vysokofrekvenčních oscilací a výčet detektorů používaných ve výzkumu. V rámci práce byly vyvinuty či vylepšeny tři detektory vysokofrekvenčních oscilací, na jejichž popis navazuje evaluace z hlediska shody s manuální detekcí, přesnosti výpočtu příznaků oscilací a schopnosti lokalizace patologické tkáně. V závěru práce jsou představeny vyvinuté metody vizualizace vysokofrekvenčních výskytu oscilací a stručně uvedeny dosažené vědecké výsledky.

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High frequency link power converters for DC – 3Φ AC applications are investigated. Low cost, reduced size, galvanic isolation and efficient large boosting of voltage level are the key motivations behind the selection of such topologies. This thesis proposes high frequency link 3Φ inverters for three wire and four wire systems. The proposed topologies have the simplest power circuit configuration and commutation requirements among all high frequency link topologies reported in the literature. A full load efficiency greater than 90% is achieved with a passive snubber. The effect of various circuit non-idealities are common and important for desirable performances of these topologies. A few such issues are highlighted. Firstly, the special commutation requirement of the power circuit causes a non-linear distortion in the output voltages and thus makes the gain of the power converter time varying. A simple compensation technique is adopted to mitigate the problem. Secondly, the high frequency transformer should operate with only switching frequency component. However, in the practical situations a significant amount of low frequency component gets injected into the transformer and results in peaky transformer magnetizing current unless it is over designed. A suitable measure is incorporated in the proposed topologies to achieve a magnetic protection. The power circuit topology is used as stand-by AC power supply. These are of interest for Uninterruptible Power Supply (UPS) and Micro-grid applications. One of the main objectives of such supplies is to provide a high quality and highly reliable power to the connected loads. A voltage regulation loop based on proportional + multiresonant controller is proposed to achieve excellent quality of the output voltage with unbalanced and nonlinear loadings. The factors influencing regulation and stability of the voltage waveform are identified and necessary modifications are carried out to improve the performance. The potential of this voltage regulation loop along with P/Q droop technique and a simple resistive virtual output impedance loop is exploited to achieve decentralized paralleling of inverters. A trade off between the output voltage power quality and the sharing accuracy is examined. The total harmonic distortion and degree of unbalance in the output voltage waveform are experimentally measured well below the specified limit for stand alone AC supplies with an excellent sharing accuracy. Some of the grid interactive modes are addressed for the completeness of the work. A shunt compensator system and a double conversion system based on the same high frequency link converter are experimentally evaluated. These systems can find their application in UPS systems. A few important observations on the power circuit performances are indicated.

[pt] As mudanças tecnológicas e regulatórias foram facilitadores para o surgimento dos investidores de alta frequência, HFTs, no mix de participantes do mercado financeiro. Como classe, estes investidores não constituem uma entidade coerente e seu impacto e contribuição para a formação do preço não é clara. Esse trabalho analisou 10 categorias de investidores, que se diferenciam por suas características de latência, a partir de uma base de dados composta por todas as ordens enviadas para o book de dólar futuro com vencimento em 1 de agosto de 2013, da Bolsa de Valores e Mercadorias e Futuros (BMFBovespa). Dentre toda as categorias de instidores testadas, a categoria HFT 1, a mais rápida de todas, foi a que apresentou o maior coeficiente de impacto no preço, 20 por cento, e a maior medida de contribuição relativa para a volatilidade fundamental, 10 por cento. / [en] Technological and regulatory changes were facilitators for the emergence of high frequency traders, HFTs, in the mix of financial market participants. As a class, these investors do not constitute a coherent entity and its impact and contribution to the price formation are not clear. This study analyzed 10 categories of investors, who are distinguished by their latency characteristics from a database comprised of all orders sent to the book of future dollar maturing on August 1, 2013, in the Brazilian Stock Exchange and Commodities and Futures Exchange (BMFBovespa). Among all the categories of investors tested, the HFT 1, the fastest of all, was the one that had the highest coefficient of impact on price, 20 per cent, and a larger measure of relative contribution to fundamental volatility, 10 per cent.

[pt] Devido às exigências da largura de banda, especialmente nas comunicações sem fios que são cada dia maiores pelo aumento do numero de usuários, é necessário estudar a banda de EHF(Extremely High Frequency). A transmissão e recepção de dados em EHF constitui uma possível solução para aliviar a escassez do espectro e satisfazer a crescente demanda de maiores velocidades tentado resolver as limitações dos sistemas atuais. As ondas de radio na banda EHF vão de 30 até 300 GHz e são chamadas ondas milimétricas, já que seus comprimentos de onda vão de 10 mm até 1 mm. Neste trabalho, a montagem de um sistema de geração e detecção de ondas de EHF a partir do batimento de dois lasers é apresentada. Técnicas de modulação e demodulação em fase, amplitude e frequência na faixa de 200-300 GHz são demonstradas. / [en] The capacity of wireless communications has started to reach the top and the unstoppable increase of users is becoming a problem because more bandwidth is needed, which has gave rise to the study of EHF (Extremely High Frequency) band. Transmission and reception of data in EHF is shown as a solution to alleviate the scarcity of the spectrum and to meet the request of faster speeds to solve the limitation of the actual systems. The range of radio waves in EHF band go from 30 to 300 GHz, and are called millimeter waves since their wavelengths are between 10mm and 1mm. In this work is presented a system capable to generate and detect EHF waves from the beating of two lasers, and at the same time different modulation and demodulation techniques (phase, amplitude and frequency) are presented.

Overconfidence and its relationship to investor market participation is well established in the finance literature. The research into investors and social networks is only in its infancy, however. This thesis extends the literature by expanding on both subjects individually, then bringing them together. Empirical work on individual investors in the existing literature links overconfidence and excess trading, resulting in impaired returns. The preferred activity metric, monthly account turnover, encapsulates two separate elements, though. One is trade frequency. The other is leverage use. Chapter 4 of this thesis theorizes based on the existing literature that in fact trade frequency is not a good measure of overconfidence. It then demonstrates through empirical analysis of a group of individual non-professional foreign exchange traders that leverage is much more suitable to that role. Chapter 5 turns the focus to social networks, particularly with respect to information transfer. The literature in finance anticipates that network members benefit from their membership. Further, network position (social capital) enhances that benefit. This thesis challenges that expectation with respect to non-professional investors. Findings based on analysis of members of an online retail foreign exchange trader social network indicate that while there may be an educational benefit accruing to unsophisticated members, for more sophisticated ones membership appears to have a negative effect on returns. One potential explanation for the negative impact of network membership is explored in Chapter 6 in the form of impression management. It is hypothesized that sophisticated investors are influenced in their behaviour by the realization they are being observed, and also the size of their audience. Analysis of foreign exchange traders indicates an increase in leverage use among sophisticated investors as their audience size increases, coinciding with a decline in trade excess returns, making the case for an observation-based rise in overconfidence.