Dissertations / Theses on the topic 'High frequency electronic applications'

The advent of large-scale graphene grown by chemical vapor deposition (CVD) offers a viable route towards high-frequency (HF) graphene-based analogue electronics. A significant challenge, however, is to synthesize and fabricate HF graphene-based devices with high carrier mobility. Here, we report our efforts to understand and control the CVD growth mechanism of graphene on copper, to characterize the synthesized film, and to fabricate graphene transistors and HF devices. In parallel, we describe the synthesis of large pristine dendritic graphene flakes that we name graphlocons. The electronic transport properties and magnetoresistance were assessed from 300 K to 100 mK and mobility up to 460 cm^2/Vs was obtained with a residual charge carrier density of 1.6x10^12 cm^-2. HF scattering parameters were measured from 0.04 to 20 GHz but they showed no dependence on temperature and magnetic field. This work provides a starting point for improving the structural and electronic properties of CVD graphene, and for exploring new phenomena in the GHz frequency range.
L'avènement du graphène produit à grande-échelle par dépôt chimique en phase vapeur (CVD) ouvre une voie vers l'électronique haute-fréquence (HF) à base de graphène. Synthétiser du graphène possédant une grande mobilité des porteurs de charge et l'incorporer à des dispositifs HF constitue cependant un important défi. Nous présentons ici le fruit de nos efforts pour comprendre et contrôler le mécanisme de croissance CVD du graphène sur le cuivre, caractériser les films ainsi produits, et fabriquer des transistors et dispositifs HF à base de graphène. Parallèlement, nous décrivons la synthèse de grands flocons dendritiques de graphène que nous appelons graphlocons. Les propriété électroniques et la magnetorésistance de ces échantillons ont été mesurées de 300 K à 100 mK et la mobilité la plus élevée obtenue est de 460 cm^2/Vs avec une densité de porteurs de charge résiduels de 1.6x10^12 cm^-2 . Les paramètres S de haute fréquence ont été mesurés de 0.04 à 20 GHz mais aucune dépendance en température ou champ magnétique n'a été observée. Ce travail fourni un point de départ pour améliorer les propriétés structurales et électroniques du graphène produit par CVD, et pour explorer de nouveaux phénomènes dans le domaine des GHz. .

The main contribution of this project was to investigate power electronics technology in designing and developing high frequency high power converters for industrial applications. Therefore, the research was conducted at two levels; first at system level which mainly encapsulated the circuit topology and control scheme and second at application level which involves with real-world applications. Pursuing these objectives, varied topologies have been developed and proposed within this research. The main aim was to resolving solid-state switches limited power rating and operating speed while increasing the system flexibility considering the application characteristics. The developed new power converter configurations were applied to pulsed power and high power ultrasound applications for experimental validation.

In this thesis, we have experimentally probed the microwave frequency electrodynamics of large area graphene, focussing on contactless measurements of graphene to extract material properties and implementation of non-reciprocal microwave devices. Our goal is to exploit interaction of graphene with electromagnetic waves in the microwave domain.By fabricating wideband graphene coplanar waveguides, we show that graphene has a constant wideband resistance from 17 Hz to 110 GHz due to negligible kinetic inductance and negligible skin effect up to 110 GHz. We characterize contact impedance between graphene and metal electrodes and our devices show that contact capacitance shorts the contact resistance above ~ 2 GHz, allowing for contactless measurements of graphene up to 110 GHz. We measured the magnetoconductance of large-area graphene under microwave excitation by employing Corbino disk geometry via the transfer of graphene films onto polished coaxial flanges. Our experimental setup allows for both passive and active graphene devices where the active devices are doped by field effect with an intrinsic silicon gate electrode transparent to microwaves. Magnetoconductive mobilities of ~ 1,000 cm2/Vs were extracted from a single component Drude model observed at high carrier density. An anomalous microwave magnetoresistance was also observed. We designed, fabricated and characterized a hollow waveguide isolator with a magnetically biased graphene acting as the non-reciprocal element via Faraday rotation. Our experimental setup allows for contactless characterization of conductivity, mobility and charge carrier density of the graphene film. Faraday rotation was measured up to 1.5° which resulted in isolation of 25 dB. We show that performance of the isolator can be improved by increasing carrier mobility in graphene. As the direction of Faraday rotation is contingent on majority charge carrier type in graphene, we give evidence that the isolation direction can be modulated and switched via field effect graphene device implemented in the hollow waveguide using a single low-power voltage source. We demonstrate the first voltage-tunable isolator with a maximum isolation of 47 dB and voltage-tunable isolation up to 26 dB. Our work suggests that other non-reciprocal devices such as circulators can be implemented compactly with graphene.
Dans cette thèse, nous avons expérimentalement sondé les micro-ondes électrodynamiques de graphène de grande surface, plus particulièrement les mesures de graphène sans contact pour en extraire les propriétés de la matière et la mise en œuvre de dispositifs non-réciproques générateurs de micro-ondes. Notre objectif consiste à exploiter l'interaction entre le graphène et les ondes électromagnétiques dans le domaine des micro-ondes. En fabriquant un guide d'ondes de graphène coplanaire à large bande, nous établissons que le graphène possède une résistance de large bande constante comprise entre 17 Hz et 110 GHz. Ceci est attribuable à l'inductivité cinétique et à l'effet pelliculaire négligeables jusqu'à 110 GHz. Nous décrivons l'impédance des contacts entre le graphène et les électrodes métalliques. Nos dispositifs démontrent que la capacitance de contact court-circuite la résistance de contact au-dessus de 2 GHz, permettant les mesures du graphène sans contact jusqu'à 110 GHz. Nous avons mesuré la conductivité magnétique du graphène à grande surface sous excitation de micro-ondes utilisant une géométrie de disque Corbino en transférant les films de graphène sur des embouts de câble coaxial polis. Notre installation permet l'utilisation de dispositifs de graphène actifs et passifs où les dispositifs actifs sont dopés par effet de champ avec une grille de silicium intrinsèque transparente aux micro-ondes. Nous avons extrait des mobilités à base de la conductivité magnétique autour de 1000 cm… en utilisant le model de Drude à une composante à haute densité. Une magnéto résistance atypique a également été observée. Nous avons créé, fabriqué et caractérisé un guide d'onde isolateur creux avec du graphène biaisé magnétiquement agissant comme élément non-réciproque par rotation de Faraday. Notre montage expérimentale permet la caractérisation sans contact de la conductivité, la mobilité et la densité de porteurs de charges du film de graphène. La rotation de Faraday a été mesuré jusqu'à 1.5 ce qui résulte en une isolation de 25dB. Nous démontrons que la performance de l'isolateur peut être améliorée en augmentant la mobilité dans le graphène. Étant donné que la direction de la rotation de Faraday dépend du signe du porteur de charge dominant dans le graphène, nous soumettons des données démontrant que la direction de l'isolation peut être modulée et changée en utilisant l'effet de champ implémenté dans le guide d'ondes creux avec une seule source de voltage à basse puissance. Notre travail suggère que d'autres dispositifs non-réciproques comme des circulateurs peuvent être implémentés de façon compacte avec du graphène.

With the emergence of the Internet of Things (IoT), wireless body area networks (WBANs) are becoming increasingly pervasive in everyday life. Most WBANs are currently working at the IEEE 802.15.4 Zigbee standard. However there are growing interests to investigate the performance of BANs operating at higher frequencies (e.g. millimetre-wave band), due to the advantages offered compared to those operating at lower microwave frequencies. This thesis aims to realise printed conductive traces on flexible substrates, targeted for high frequency wearable electronics applications. Specifically, investigations were performed in the areas pertaining to the surface modification of substrates and the electrical performance of printed interconnects. Firstly, a novel methodology was proposed to characterise the dielectric properties of a non-woven fabric (Tyvek) up to 20 GHz. This approach utilised electromagnetic (EM) simulation to improve the analytical equations based on transmission line structures, in order to improve the accuracy of the conductor loss values in the gigahertz range. To reduce the substrate roughness, an UV-curable insulator was used to form a planarisation layer on a non-porous substrate via inkjet printing. The results obtained demonstrated the importance of matching the surface energy of the substrate to the ink to minimise the ink de-wetting phenomenon, which was possible within the parameters of heating the platen. Furthermore, the substrate surface roughness was observed to affect the printed line width significantly, and a surface roughness factor was introduced in the equation of Smith et al. to predict the printed line width on a substrate with non-negligible surface roughness (Ra ≤ 1 μm). Silver ink de-wetting was observed when overprinting silver onto the UV-cured insulator, and studies were performed to investigate the conditions for achieving electrically conductive traces using commercial ink formulations, where the curing equipment may be non-optimal. In particular, different techniques were used to characterise the samples at different stages in order to evaluate the surface properties and printability, and to ascertain if measurable resistances could be predicted. Following the results obtained, it was demonstrated that measurable resistance could be obtained for samples cured under an ambient atmosphere, which was verified on Tyvek samples. Lastly, a methodology was proposed to model for the non-ideal characteristics of printed transmission lines to predict the high frequency electrical performance of those structures. The methodology was validated on transmission line structures of different lengths up to 30 GHz, where a good correlation was obtained between simulation and measurement results. Furthermore, the results obtained demonstrate the significance of the paste levelling effect on the extracted DC conductivity values, and the need for accurate DC conductivity values in the modelling of printed interconnects.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.
Vita.
Includes bibliographical references.
There are numerous advantages to high frequency (high field) electron paramagnetic resonance (EPR) spectroscopy. Two of the most important are improved sensitivity and the improved resolution of field dependent interactions. In addition, there are many attractive features to time domain spectroscopy. Pulsed EPR allows for the design of experiments, which can specifically be used to study structure and dynamics of paramagnetic species and provide utmost resolution by separating interactions from each other. The combination of pulsed techniques and high frequencies is not only complimentary to continuous wave (CW) low frequency EPR but it also greatly increases the accessible information on paramagnetic species. High frequency, time domain EPR is still in its infancy. Spectrometers at W-band ([approximately] 95 GHz) are now available commercially but to date very few spectrometers operating at higher frequencies have been described. The spectrometer developed in the Francis Bitter Magnet Laboratory operates at a microwave (MW) frequency of 139.5 GHz corresponding to [approximately] 5 T magnetic field. The applications presented in this thesis illustrate the potential of high frequency, time domain EPR spectroscopy at 139.5 GHz in obtaining structural and mechanistic insights of several paramagnetic systems. Well resolved EPR spectra observed at 139.5 GHz of the stable tyrosine radical in ribonucleotide reductase (RNR) revealed the existence of a hydrogen bond in RNR from yeast, chapter 1. The bond length and orientation were determined from the nuclear frequencies of the proton, detected by orientation selective electron nuclear double resonance (ENDOR).
(cont.) The advantage of the time domain detection scheme is demonstrated in chapters 4, 5 and 6. A stimulated echo sequence is used to separate different organic radicals associated with the reduction chemistry and inhibition mechanisms of RNR. Using the dispersion in relaxation rates at high temperature ([approximately] 60 K) it is possible to filter the multi component spectrum. The assignment of new radicals is possible at high field, 5 T, due to the high resolution in g anisotropy. The findings support earlier proposals for the mechanism of nucleotide reduction and inhibition of this very important enzyme. To study photoexcited triplet molecules a light source was coupled to the high frequency spectrometer and the pulsed mode detection scheme was used to acquire EPR spectra. The new technique is demonstrated on several model systems. In addition to the basic advantages described above, high frequency EPR opens new frontiers for high spin systems, S >[or equal to] 1, with large spin-spin interaction. Because of the inverse field dependency of the zero field splitting, such systems may be totally EPR-silent at normal EPR frequencies. However their EPR spectra are accessible at high frequencies due to the reduction of linewidth. The Mn(II), S = 5/2, in superoxide dismutase (SOD) is a good example for such system.
by Galit Bar.
Ph.D.

The new generation of automotive controllers requires a space-constrained and high-efficiency step-down architecture. Hence, recently a potential alternative for the conventional step-down topologies is highly demanded. The new architecture should meet the high power density, high efficiency, wide operating ranges, high EMI capabilities, and low-cost requirements. This thesis, developed at the University of Padova and sponsored by Infineon Technologies, aims at investigating potential candidate topologies for automotive step-down conversion capable of eliminating or offsetting some of the common shortcomings of conventional solutions currently in use. Many research effort is paid for the soft switching quasi-resonant topologies in order to miniaturize the passive components through the switching frequency increase. However, the variable switching frequency, increased components count, and narrow operating ranges prevent the wide adoption of the quasi-resonant topologies in the target application. The first objective of this project is to investigate the quasi-resonant buck converter topology in order to stand on the limitations and operating conditions boundaries of such topology. The digital efficiency optimization technique, which is developed in this work, extends the operating ranges in addition to reduce operating frequency variations. On the other hand, the multilevel hybrid topologies are potentially able to meet the aforementioned requirements. By multiplying ripple frequency and fractioning voltage across the switching node the multilevel topologies have the direct advantage of reduced passive components. Moreover, multilevel topologies have many other attractive features include reduced MOSFET voltage rating, fast transient response, a Buck-like wide range voltage conversion ratio, and improved efficiency. These features candidate the multilevel topologies, in particular, the three-level flying-capacitor converter, as an innovative alternative for the conventional topologies for the target application. Accordingly, the three-level flying-capacitor converter (3LFC) is investigated as a second objective for this project. Flying-capacitor (FC) voltage balancing in such topology is quite challenging. The 3LFC under valley current mode control shows an interesting performance, where the FC voltage is self-balanced. In this work, the stability of the converter under valley and peak current mode control is studied and a simplified stability criterion is proposed. The proposed criterion address both current loop static stability and FC voltage stability. The valley current mode modulator results to be inherently stable as soon as the current static instability is compensated with an external ramp. On contrary, the FC voltage in peak current mode control (P-CMC) will never be balanced unless the converter operated with relatively high static peak-to-peak inductor current ripple. Since P-CMC has an inherent over-current protection feature, P-CMC based architectures are widely used in the industrial applications. However, in practice the peak current controlled three-level converter is inherently unstable. Consequently, the instability of the P-CMC 3LFC is addressed. A sensorless stabilizing approach, with two implementation methodologies, is developed in this work. The proposed technique eliminates the instability associated with the FC voltage runaway, in addition to FC voltage self-balancing. Moreover, the proposed methodology offers reduced size, less complexity, and input voltage independent operation. Besides, the proposed approach can be extended to system with a higher number of voltage levels with minimal hardware complexity. The proposed techniques and methodologies in this work are validated using simulation models and experimentally. Finally, in the conclusions the results of the Ph.D. activity are summarized and recommendations for the further development are outlined.

Practical steady-state and dynamic design and analysis for high-order dc/dc resonant converters is presented. The analysis is mainly based on two types of the resonant converters, parallel-type and Class-D (a series-type), which are suitable for high-frequency applications. In the analysis of parallel resonant converters, the key step in the derivation of steady-state analytic equations for LLC-type parallel (LLC-PRC) and LLCC-type series-parallel resonant converter (LLCC-SPRC) is to reduce the order of their state-space models. In particular, the analytic equations for LLCC-SPRC can also be used to design and analyze the LC-PRC, LLC-PRC, and LCC-type series-parallel resonant converters. A simple design procedure along with design examples is given based on the derived analytic equations. Experimental LLC-PRC and LLCC-SPRC are implemented to verify the design results. In the analysis of the zero-voltage switch (ZVS) Class-D converter, both steady-state and dynamic analysis methods are presented. The analysis is based on the Class-D converter with a variable capacitance switch (VCS) for voltage regulation at constant frequency. A generalized DC model for steady-state and dynamic analysis of the converter is given. A simplified small-signal model is found from perturbing the DC model and can be used to predict the low-frequency dynamic control- and line-to-output transfer functions. To predict the high-frequency dynamics, two models are derived based on the amplitude and phase modulations from communication theory. Besides the steady-state and small-signal modeling, a strategy to achieve a stable loop gain for closed-loop operation is addressed. A compensation controller for closed-loop operation of the VCS is developed. All the calculated and design results of the dynamic responses are verified based on the experimental measurements from the prototype converter.

RFIC's are traditionally implemented in III--V compounded semiconductors or in bipolar technologies, due to their superior RF performances (e.g. low noise) when compared to CMOS technologies. The challenges are not only to design RF transceivers in standard CMOS processes, but also to establish design methodologies and optimization techniques for their building blocks.
This thesis is concerned with one of the key building blocks, namely the Low Noise Amplifier (LNA). Several low-voltage LNA's were successfully implemented in a standard 0.18 mum CMOS technology, operating in the 5--9 GHz frequency band, targeted for future wireless applications. A new and very simple gain control mechanism is suggested for the first time, which does not affect the optimum noise and impedance matching. The 8--9 GHz prototypes are the highest LNA frequencies reported to-date in CMOS. All prototypes exhibit gain tuning ranges of over 10 dB, and can operate from a supply voltage as low as 0.7 V.
A design strategy for optimizing RF passive components (e.g. inductors, capacitors, and varactors) beyond 5 GHz is presented.
An attempt is made to explore the possibility of using Micro-Electro Mechanical Systems (MEMS) in the RF arena. (Abstract shortened by UMI.)

This thesis has investigated the reduction of audible noise in low speed sensorless controlled drives for automotive electrical power steering (EPS) applications. The specific methods considered employ saliency tracking high frequency (hf) voltage injection in the machine's estimated d axis. In terms of the audible noise reduction, a novel random sinusoidal hf injection sensorless method has been proposed. The perceived audible noise due to the hf injection can be reduced by randomly distributing the injection frequencies around a centre frequency, such that it is perceived as a background hiss rather than the fixed tone heard with fixed hf injection methods. By analysing the A-weighting scales used to classify human perception of audible noise and frequency analysis of the recorded noise, an injection frequency of (lS00±328) Hz is found to have the lowest audible noise level compared to other random frequencies and other fixed frequencies methods. A 10 kHz square wave hf injection sensorless method has also been implemented. The frequency analysis of the recorded audible noise indicates that it also may be lower than for the fixed hf sinusoidal injection. In terms of control performance, sensorless torque control for these methods has been achieved from zero speed to ±240rpm with up to ±60A load (about 63% rated load). Similar position estimate quality has been demonstrated. Dynamic performance for a step change in torque current demand and for a speed reversal has been performed, and the random injection method with (1S00±328) Hz frequency has been found to be able to control a step change in torque demand current of 50A whilst for the 10kHz square wave injection method only a 40A step change can be achieved. On the other hand, the average position error after the speed transient has settled is less for the 10 kHz square ewave injection than for the random injection.

An investigation into the feasibility of designing a monolithic high frequency voltage controlled oscillator is performed. With design constraints of an oscillator Q between 5 and 10 and minimal chip area, the resonant LC tank and negative resistive cross coupled differential amplifier circuit is analyzed and design guidelines are developed. Analysis of the circuit encompasses both linear and non-linear modes of operation of the circuit, predicts the fundamental frequency of oscillation, and highlights design limitations for the resonant elements in terms of meeting the Q specifications at higher frequencies. Experimental results on a fixed frequency version of the VCO circuit yielded good agreement with theoretical analysis. For the parameters tested, the error was on the order of 10% in most cases.

Five chapters of this dissertation concentrate on the characterization and cancellation of high frequency parasitic parameters in EMI filters. One chapter addresses the interaction between the power interconnects and the parasitic parameters in EMI filters. The last chapter addresses the characterization, evaluation and design of noise separators. Both theoretical and experimental analyses are applied to each topic. This dissertation tries to explore several important issues related to EMI filters and noise separators. The author wishes to find some helpful approaches to benefit the understanding and design of EMI filters. The contributions of the dissertation can be summarized below: 1) Identification of mutual couplings and their effects on EMI filter performance 2) Extraction of mutual couplings using scattering parameters 3) Cancellation of mutual couplings to improve EMI filter performance 4) Cancellation of equivalent series inductance to improve capacitor performance 5) Analysis of mode transformations due to the imperfectly balanced parameters in EMI filters 6) Analysis of interaction between power interconnects and EMI filters on filter high-frequency performance 7) Modeling and design of high-performance noise separator for EMI diagnosis 8) Identification of the effects of parasitics in boost PFC inductor on DM noise Although all topics are supported by both theory and experiments, there may still be some mistakes in the dissertation. The author welcomes any advice and comments. Please send them via email to shuowang@ieee.org. Thanks
Ph. D.

Abstract The most important paradigms in quantum mechanics are probably a twolevel system, a harmonic oscillator and an ideal (infinite) periodic potential. The first two provide a starting point for understanding the phenomena in systems where the spectrum of energy levels is discrete, whereas the last one results in continuous energy bands. Here an attempt is made to study the dynamics of the electrons in a narrow miniband of a semiconductor superlattice under electric and magnetic fields. Semiconductor superlattices are artificial periodic structures, where certain properties like the period and the energy band structure, defined in standard crystals by the nature, can be controlled. Electron dynamics in a single superlattice miniband is interesting both from the viewpoint of fundamental and applied physics. From the fundamental perspective superlattices serve as a model system for a wealth of phenomena resulting from the wavenature of charge carriers. On the other hand, superlattices can potentially be utilized in oscillators and amplifiers operating at THz frequencies. They can, in principle, provide a reasonable THz Bloch gain under dc bias and parametric amplification in the presence of ac pump field. Because of numerous scientific and technological applications in different areas of science and technology, including astrophysics and atmospheric science, biological and medical sciences, and detection of concealed weapons and biosecurity, a construction of compact tunable THz amplifiers and generators that can operate at room temperature is an important – but so far unrealized – task. This thesis focuses on the influence of electric and magnetic fields on small-signal absorption and gain in semiconductor superlattices in the presence of dissipation (scattering). We present several new ideas how the effects arising due to the wave nature of the electrons can be utilized in an operation of THz oscillators and amplifiers. In Papers I–V, we discuss the properties of superlattice sub-THz and THz parametric amplifiers, whereas the Papers VI–IX are devoted to the problem of domain instability in the realization of cw THz Bloch oscillator. In Paper IX we also establish a feasibility of new type of superlattice THz amplifier based on nonlinear cyclotron-like oscillations of the miniband electrons. The ideas presented in the Papers I–IX are supplemented here with a detailed discussion of the physical origin of the effects and more rigorous mathematical derivations of the main equations.

With the explosive growth of the wireless market, the demand for low-cost and highly-integrated radio frequency (RF) transceiver has been increased. Keeping up with this trend, complimentary metal-oxide-semiconductor (CMOS) has been spotlighted by virtue of its superior characteristics. However, there are challenges in achieving this goal, especially designing the transmitter portion. The objective of this research is to demonstrate the feasibility of fully integrated CMOS transmitter module which includes power amplifier (PA) and transmit/receive (T/R) switch by compensating for the intrinsic drawbacks of CMOS technology. As an effort to overcome the challenges, the high-power handling T/R switches are introduced as the first part of this dissertation. The proposed differential switch topology and feed-forward capacitor helps reducing the voltage stress over the switch devices, enabling a linear power transmission. With the high-power T/R switches, a new transmitter front-end topology - differential PA and T/R switch topology with the multi-section PA output matching network - is also proposed. The multi-stage PA output matching network assists to relieve the voltage stress over the switch device even more, by providing a low switch operating impedance. By analyzing the power performance and efficiency of entire transmitter module, design methodology for the high-power handling and efficient transmitter module is established. Finally, the research in this dissertation provides low-cost, high-power handling, and efficient CMOS RF transmitter module for wireless applications.

[EN] Different electronic interfaces have been proposed to measure major parameters for the characterization of quartz crystal microbalance (QCM) during the last two decades. The measurement of the adequate parameters of the sensor for a specific application is very important, since an error in this measure can lead to an error in the interpretation of the results. The requirements of the system of characterization depend on the application. In this thesis we propose two characterization systems for two types of applications that involve the majority of sensor applications: 1) Characterization of materials under variable damping conditions and 2) Detection of substances with high measurement resolution. The proposed systems seek to solve the problems detected in the systems currently in use. For applications in which the sensor damping varies during the experiment, we propose a system based on a new configuration of the technique of automatic capacitance compensation (ACC). This new configuration provides the measure of the series resonance frequency, the motional resistance and the parallel capacitance of the sensor. Moreover, it allows an easy calibration of the system that improves the precision in the measurement. We show the experimental results for 9 and 10 MHz crystals in fluid media, with different capacitances in parallel, showing the effectiveness in the capacitance compensation. The system presents some deviation in frequency with respect to the series resonance frequency, as measured with an impedance analyser. These deviations are due to the non-ideal, specific behaviour of some of the components of the circuit. A new circuit is proposed as a possible solution to this problem. For high-resolution applications we propose an integrated platform to characterize high-frequency acoustic sensors. The proposed system is based on a new concept in which the sensor is interrogated by means of a very stable, low-noise external source at a constant frequency, while the changes provoked by the charge in the phase of the sensor are monitored. The use of high-frequency sensors enhances the sensitivity of the measure, whereas the design characterization system reduces the noise in the measurement. The result is an improvement in the limit of detection (LOD). This way, we achieve one of the challenges in the acoustic high-frequency devices. The validation of the platform is performed by means of an immunosensor based in high fundamental frequency QCM crystals (HFF-QCM) for the detection of two pesticides: carbaryl and thiabendazole. The results obtained for carbaryl are compared to the results obtained by another high-frequency acoustic technology based in Love sensors, with the optical technique based in surface plasmonic resonance and with the gold standard technique Enzyme Linked Immunoassay (ELISA). The LOD obtained with the acoustic sensors HFF-QCM and Love is similar to the one obtained with ELISA and improves by one order of magnitude the LOD obtained with SPR. The conceptual ease of the proposed system, its low cost and the possibility of miniaturization of the quartz resonator, allows the characterization of multiple sensors integrated in an array configuration, which will allow in the future to achieve the challenge of multianalyte detection for applications of High-Throughput Screening (HTS).
[ES] Durante las dos últimas décadas se han propuesto diferentes interfaces electrónicos para medir los parámetros más importantes de caracterización de los cristales de microbalanza de cuarzo (QCM). La medida de los parámetros adecuados del sensor para una aplicación específica es muy importante, ya que un error en la medida de dichos parámetros puede resultar en un error en la interpretación de los resultados. Los requerimientos del sistema de caracterización dependen de la aplicación. En esta tesis se proponen dos sistemas de caracterización para dos ámbitos de aplicación que comprenden la mayoría de las aplicaciones con sensores QCM: 1) Caracterización de materiales bajo condiciones de amortiguamiento variable y 2) detección de sustancias con alta resolución de medida. Los sistemas propuestos tratan de resolver la problemática detectada en los ya existentes. Para aplicaciones en las que el amortiguamiento del sensor varía durante el experimento, se propone un sistema basado en una nueva configuración de la técnica de compensación automática de capacidad (ACC). La nueva configuración proporciona la medida de la frecuencia de resonancia serie, la resistencia dinámica y la capacidad paralelo del sensor. Además, permite una fácil calibración del sistema que mejora la precisión en la medida. Se presentan resultados experimentales para cristales de 9 y 10MHz en medios fluidos, con diferentes capacidades en paralelo, demostrando la efectividad de la compensación de capacidad. El sistema presenta alguna desviación en frecuencia con respecto a la frecuencia resonancia serie, medida con un analizador de impedancias. Estas desviaciones son explicadas convenientemente, debidas al comportamiento no ideal específico de algunoscomponentes del circuito. Una nueva propuesta de circuito se presenta como posible solución a este problema. Para aplicaciones de alta resolución se propone una plataforma integrada para caracterizar sensores acústicos de alta frecuencia. El sistema propuesto se basa en un nuevo concepto en el que el sensor es interrogado, mediante una fuente externa muy estable y de muy bajo ruido, a una frecuencia constante mientras se monitorizan los cambios producidos por la carga en la fase del sensor. El uso de sensores de alta frecuencia aumenta la sensibilidad de la medida, por otro lado, el sistema de caracterización diseñado reduce el ruido en la misma. El resultado es una mejora del límite de detección (LOD). Se consigue con ello uno de los retos pendientes en los dispositivos acústicos de alta frecuencia. La validación de la plataforma desarrollada se realiza con una aplicación de un inmunosensor basado en cristales QCM de alta frecuencia fundamental (HFF-QCM) para la detección de dos pesticidas: carbaryl y tiabendazol. Los resultados obtenidos para el Carbaryl se comparan con los obtenidos con otra tecnología acústica de alta frecuencia basada en sensores Love, con la técnica óptica basada resonancia superficial de plasmones (SPR) y con la técnica de referencia Enzyme Linked Immuno Assay (ELISA). El LOD obtenido con los sensores acústicos HFFQCM y Love es similar al obtenido con las técnicas ELISA y mejora en un orden de magnitud al obtenido con SPR. La sencillez conceptual del sistema propuesto junto con su bajo coste, así como la capacidad de miniaturización del resonador de cuarzo hace posible la caracterización de múltiples sensores integrados en una configuración en array, esto permitirá en un futuro alcanzar el reto de la detección multianalito para aplicaciones High-Throughput Screening (HTS).
[CAT] Durant les dues últimes dècades s'han proposat diferents interfases electrònics per a mesurar els paràmetres més importants de caracterització dels cristalls de microbalança de quars (QCM). La mesura dels paràmetres adequats del sensor per a una aplicació específica és molt important, perquè un error en la interpretació dels resultats pot resultar en un error en la interpretació dels resultats. Els requeriments del sistema de caracterització depenen de l'aplicació. En aquesta tesi, es proposen dos sistemes de caracterització per a dos àmbits d'aplicació que comprenen la majoria de les aplicacions amb sensors QCM: 1) Caracterització de materials sota condicions d'amortiment variable i 2) detecció de substàncies amb alta resolució de mesura. Els sistemes proposats tracten de resoldre la problemàtica detectada en els ja existents. Per a aplicacions en les quals l'amortiment del sensor varia durant l'experiment, es proposa un sistema basat en una nova configuració de la tècnica de compensació automàtica de capacitat (ACC). La nova configuració proporciona la mesura de la freqüència de ressonància sèrie, la resistència dinàmica i la capacitat paral¿lel del sensor. A més, permet un calibratge fàcil del sistema que millora la precisió de la mesura. Es presenten els resultats experimentals per a cristalls de 9 i 10 MHz en mitjans fluids, amb diferents capacitats en paral¿lel, demostrant l'efectivitat de la compensació de capacitat. El sistema presenta alguna desviació en freqüència respecte a la freqüència ressonància sèrie, mesurada amb un analitzador d'impedàncies. Aquestes desviacions són explicades convenientment, degudes al comportament no ideal específic d'alguns components del circuit. Una nova proposta de circuit es presenta com a possible solució a aquest problema. Per a aplicacions d'alta resolució es proposa una plataforma integrada per a caracteritzar sensors acústics d'alta freqüència. El sistema proposat es basa en un nou concepte en el qual el sensor és interrogat mitjançant una font externa molt estable i de molt baix soroll, a una freqüència constant mentre es monitoritzen els canvis produïts per la càrrega en la fase del sensor. L'ús de sensors d'alta freqüència augmenta la sensibilitat de la mesura, per altra banda, el sistema de caracterització dissenyat redueix el soroll en la mateixa. El resultat és una millora en el límit de detecció (LOD). S'aconsegueix amb això un dels reptes pendents en els dispositius acústics d'alta freqüència. La validació de la plataforma desenvolupada es realitza amb una aplicació d'un immunosensor basat en cristalls QCM d'alta freqüència fonamental (HFF-QCM) per a la detecció de dos pesticides: carbaryl i tiabendazol. Els resultats obtinguts per al carbaryl es comparen amb els obtinguts amb altra tecnologia acústica d'alta freqüència basada en sensors Love, amb la tècnica òptica basada en ressonància superficial de plasmons (SPR) i amb la tècnica de referència Enzyme Linked Immuno Assay (ELISA). El LOD obtingut amb els sensors acústics HFF-QCM i Love és similar al obtingut amb les tècniques ELISA i millora en un ordre de magnitud el obtingut amb SPR. La senzillesa conceptual del sistema proposat junt amb el seu baix cost, així com la capacitat de miniaturització del ressonador de quars fa possible la caracterització de múltiples sensors integrats en una configuració en array, el que permetrà en un futur assolir el repte de la detecció multianalit per a aplicacions High-Throughput Screening (HTS).
García Narbón, JV. (2016). Improved characterization systems for quartz crystal microbalance sensors: parallel capacitance compensation for variable damping conditions and integrated platform for high frequency sensors in high resolution applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63249
TESIS

Les nano-applications utilisant des faisceaux d'ions focalisés nécessitent des sources d'ions à haute brillance avec une faible dispersion en énergie (ΔE) ce qui permet une excellente résolution latérale et un courant d'ions suffisamment élevé pour induire des vitesses d'érosion raisonnables et des rendements élevés d'émission électronique et ionique. Les objectifs de cette thèse sont le développement d'une source d'ions basée sur l'impact électronique ayant une brillance réduite Br de 10³ – 10⁴ A m⁻² sr ⁻ ¹ V⁻ ¹, une dispersion en énergie ΔE ≲ 1 eV et un choix polyvalent d'ions. Le premier concept évalué consiste à focaliser un faisceau d'électrons à une énergie de 1 keV entre deux électrodes parallèles distant de moins d'un millimètre. Le volume d'ionisation « micrométrique » est formé au-dessus d'une ouverture d'extraction de quelques dizaines de µm. En utilisant un émetteur d'électrons LaB₆ et une pression de 0.1 mbar dans la région d'ionisation, Br est proche de 2.10² A m⁻² sr ⁻ ¹ V ⁻ ¹ avec des tailles de source de quelques µm, des courants de quelques nA pour Ar⁺/Xe⁺/O₂ ⁺ et une dispersion en énergie ΔE < 0.5 eV. La brillance réduite Br est encore en dessous de la valeur minimum de notre objectif et la pression de fonctionnement très faible nécessaire pour l'émetteur LaB₆ ne peut être obtenue avec une colonne d'électrons compacte, donc ce prototype n'a pas été construit.Le deuxième concept de source d'ions évalué est basé sur l’idée d’obtenir un faisceau ionique à fort courant avec une taille de source et un demi-angle d’ouverture similaire aux résultats du premier concept de source, mais en changeant l’interaction électron-gaz et la collection des ions. Des études théoriques et expérimentales sont utilisées pour l’évaluation de la performance de ce deuxième concept et de son utilité pour les nano-applications basées sur des faisceaux d'ions focalisés
High brightness low energy spread (ΔE) ion sources are needed for focused ion beam nano-applications in order to get a high lateral resolution while having sufficiently high ion beam currents to obtain reasonable erosion rates and large secondary electron/ion yields. The objectives of this thesis are: the design of an electron impact ion source, a reduced brightness Br of 10³ – 10⁴ A m⁻² sr⁻ ¹ V⁻ ¹ with an energy distribution spread ΔE ≲ 1 eV and a versatile ion species choice. In a first evaluated concept an electron beam is focussed in between two parallel plates spaced by ≲1 mm. A micron sized ionisation volume is created above an extraction aperture of a few tens of µm. By using a LaB₆ electron emitter and the ionisation region with a pressure around 0.1 mbar, Br is close to 2.10² A m⁻² sr ⁻ ¹ V ⁻ ¹ with source sizes of a few µm, ionic currents of a few nA for Ar⁺/Xe⁺/O₂ ⁺ and the energy spread being ΔE < 0.5 eV. The determined Br value is still below the minimum targeted value and furthermore the main difficulty is that the needed operation pressure for the LaB₆ emitter cannot be achieved across the compact electron column and therefore a prototype has not been constructed. The second evaluated source concept is based on the idea to obtain a high current ion beam having a source size and half-opening beam angle similar to the first concept, but changing the electron gas interaction and the ion collection. Theoretical and experimental studies are used to evaluate the performance of this second source concept and its usefulness for focused ion beam nano-applications

Le travail presente dans ce memoire a pour objet principal l'etude des phenomenes de bruit du fond electrique basse frequence dans des transistors pour applications micro-ondes de type effet de champ (HEMT) sur SiGe et GaN ainsi que de type bipolaire a heterojonction (TBH) a base de silicium-germanium (SiGe). Dans un premier chapitre nous rappelons les caracteristiques et proprietes essentielles des sources de bruit en exces que l'on rencontre generalement dans ce type de composants et proposons une description des bancs de mesure de bruit mis en oeuvre. Dans les deuxieme et troisieme chapitres, nous proposons une analyse detaillee de l'evolution du bruit observe en fonction de la frequence, de la polarisation, et de la geometrie sur des HEMTs des deux familles technologiques SiGe et GaN. Nous avons en particulier etudie les deux generateurs de bruit en courant en entree et en sortie respectivement iG et iD ainsi que leur correlation. Ceci nous a permis, en nous appuyant aussi sur l'analyse des caracteristiques statiques des transistors, d'identifier les diverses sources de bruit en exces presentes dans ces composants et de faire des hypotheses sur leurs origines. Le dernier chapitre est consacre aux TBHs a base de SiGe. Dans une premiere partie nous etablissons comment varie le bruit basse frequence de TBHs, fabriques par un premier constructeur, en fonction de la polarisation, de la geometrie et de la fraction molaire de germanium. Dans une seconde partie nous mettons en evidence, d'apres nos observations effectuees sur des TBHs fabriques par un second constructeur, l'impact important sur le bruit BF de stress thermiques appliques sur ce type de composants.

The aim of this Thesis was to try to develop an understanding of the growth and fabrication of Double Barrier Resonant Tunnelling (DBRT) diodes, in order to enhance their properties at millimetre wave frequencies (ie. above 35GHz). Chapter 1 introduces the DBRT diode and outlines some of its applications while Chapter 2 describes aspects of device fabrication. Chapter 3 discusses the solid-state and quantum mechanical aspects which determine the DBRT's current-voltage characteristics and Chapter 4 describes an extensive parametric study relating the device properties to the high frequency behaviour. Chapter 5 covers the applications of DBRT devices at high frequencies and presents some of the results achieved so far. Besides the primary objective of studying the properties which determine the high frequency application of DBRT devices (via. the characterization of an extensive range of structures grown for the project), the other goal was to try to improve upon the results of other workers in terms of generating power and to improve the efficiency of up and down conversion at millimetre wave frequencies. Perhaps the most promising application of DBRT devices is as self-oscillating mixers (SOM) which can also provide conversion gain (due to the wide bandwidth of the negative differential resistance) at the intermediate frequency. This is of great importance since it negates the need to generate a local oscillator signal and dispenses with complicated image rejection mixer arrangements (for superheterodyne mixing) and amplification stages, which are very difficult to build and are expensive at millimetre wave frequencies. Whilst working in collaboration with staff at the University of Leeds, department of Electronic and Electrical Engineering a SOM was fabricated on microstrip which gave a modest gain at around 10GHz. Similarly a DBRT diode was operated in waveguide at 106GHz and provided -9.8dBm of power as measured on a spectrum analyzer. Both of these results represent (to the authors knowledge) the best results currently seen for DBRT devices in the UK and Europe.

For many years, power electronics in the high-power area was performed with extremely slow semiconductor switches. These switches, including the thyristor and the Gate Turn-Off (GTO) thyristor, had the capacity to handle very high voltages and currents but lacked the ability to perform high frequency switching. Low-power converters, such as computer power supplies and low horsepower motor drives, have employed high-frequency switching for years and have benefited from very nice output waveforms, good control dynamic performance, and many other advantages compared to low frequency switching. Recent improvements in high-power semiconductor technology has brought switching performance similar to that of the low-power MOSFETs and IGBTs to the high-power area through the advancement of the IGBT's ratings to create the High Voltage IGBT (HVIGBT) and the development of new GTO-derived devices including the Integrated Gate Commutated Thyristor (IGCT) and the Emitter Turn-Off (ETO) thyristor. These new devices all feature high switching speed and the capability to turn off without the requirement for a turn-off snubber. With these new device technologies the high-power field of power electronics can realize dramatic improvements in the performance of systems for utility applications and motor drives. However, with these high-speed switches come new issues relating to noise, protection, performance of diodes, and thermal management in high-frequency applications. This thesis addresses the application of these new devices, especially the ETO and the IGCT. Examples of each device technology (IGBT, IGCT, and ETO) have been characterized in both their switching performance and conduction loss. The tests performed show how these new devices may be applied to various applications. The switching loss, especially related to turn-off, is the dominant factor in the power dissipation of the high-power switches, so knowledge of these characteristics are very important in the system design. To demonstrate the operation of the ETO, two power converters were constructed. The first was a 100 kW DC/DC converter, which demonstrated the operation of the ETO in a typical building block configuration, the half-bridge. The second system, a 1 MegaVolt-Amp (MVA) three-phase inverter, demonstrated the ETO in an application where the switching frequency and power level were both high. The test results demonstrate the expected characteristics of the high-frequency converters. The development of the ETO's gate driver is described. During the inverter testing, a new failure mode was found involving a parasitic diode within the ETO. This failure mode was analyzed and solutions were proposed. One of the proposed solutions was implemented and there were no more failures of this type. Another possible failure mode regarding a circulating current in an IGCT-based system is also analyzed. Soft-switching techniques can help reduce the switching loss in power semiconductor switches. Several topologies were considered for application in the high-power area, and one was selected for further investigation. A prototype Zero Current Transition (ZCT) circuit was developed using an IGCT as the main switch. The turn-off loss was reduced dramatically through the tested ZCT circuit, and the diode recovery was also alleviated.
Master of Science

Les semi-conducteurs nitrures (AlN, GaN, InN) focalisent une activité de recherche intense en raison de nombreuses applications comme les diodes électroluminescentes, les composants de puissance ou hyperfréquence. Dans cette recherche, nous avons abordé le travail sous deux angles: a) la conduction électrique dans les couches d'InN produites par croissance épitaxiale aux jets moléculaires assistée par plasma (PAMBE) et une recherche sur l'origine de la forte émission bleue dans les puits de quantiques d'InGaN/GaN. L'accumulation d'électron en surface dans les couches d'InN constitue une limitation importante pour la fabrication de composants. Au cours de ce travail, nous avons exploré l'utilisation des mesures de bruit de basse fréquence sur les couches d'InN et pu accéder à leur conductivité électrique en volume. L'étude des puits quantiques d'InGaN/GaN, obtenue par croissance épitaxiale aux jets moléculaires (MBE) ou épitaxie en phase vapeurs aux organométalliques (MOVPE) , a été effectuée par analyses de la microstructure par microscopie électronique en transmission (MET, HRTEM et STEM) en corrélation avec les propriétés optiques d'un grand nombre d'échantillons provenant de conditions de croissance différentes. Ce travail nous a permis d'acquérir une vision plus critique du rôle des conditions de fabrication et des paramètres comme la morphologie, les fluctuations de composition et la présence des défauts en V sur les explications actuellement avancées pour la forte efficacité d'émission dans les puits quantiques d' InGaN/GaN
The nitride semiconductors (AlN, GaN, InN) are subject to a large research effort due to their numerous applications, such as light emitting diodes, high power and high frequency components. Following the trend, the aim of this dissertation has been twofold: first, we have probed the bulk electrical conduction in InN layers, second, we investigated the origin of the high emission efficiency in InGaN/GaN Quantum Wells (QWs). The surface electron accumulation in InN layers is still an important limitation to device applications. W have explored this point using low frequency noise measurements on Plasma Assisted Molecular Beam Epitaxy (PAMBE) InN layers and we demonstrated that the bulk electrical conductivity of InN can be accessed. The investigation of quantum wells produced by molecular beam epitaxy (MBE) or matalorganic vapour phase epitaxy (MOVPE), has been carried out through microstructural analyses by transmission electron microscopy techniques(TEM, HRTEM, STEM) in correlation with optica properties on a large number of samples grown in different growth conditions. This experimental work has allowed us to obtain a critical view on the role of the growth conditions and such parameters as the well morphology, composition fluctuations, as well as the V shaped defects on the current explanations of high emission efficiency in InGaN/GaN QWs

In digital signal processing field, for recovering the signal without distortion, Shannon sampling theory must be fulfilled in the traditional signal sampling. However, in some practical applications, it is becoming an obstacle because of the dramatic increase of the costs due to increased volume of the storage and transmission as a function of frequency for sampling. Therefore, how to reduce the number of the sampling in analog to digital conversion (ADC) for wideband and how to compress the large data effectively has been becoming major subject for study. Recently, a novel technique, so-called “compressed sampling”, abbreviated as CS, has been proposed to solve the problem. This method will capture and represent compressible signals at a sampling rate significantly lower than the Nyquist rate.   This paper not only surveys the theory of compressed sampling, but also simulates the CS with the software Matlab. The error between the recovered signal and original signal for simulation is around -200dB. The attempts were made to apply CS. The error between the recovered signal and original one for experiment is around -40 dB which means the CS is realized in a certain extent. Furthermore, some related applications and the suggestions of the further work are discussed.

Le travail présenté dans ce mémoire a pour objet principal l’étude des phénomènes de bruit du fond électrique basse fréquence dans des transistors pour applications micro-ondes de type effet de champ (HEMT) sur SiGe et GaN ainsi que de type bipolaire à hétérojonction (TBH) à base de silicium-germanium (SiGe). Dans un premier chapitre nous rappelons les caractéristiques et propriétés essentielles des sources de bruit en excès que l’on rencontre généralement dans ce type de composants et proposons une description des bancs de mesure de bruit mis en oeuvre. Dans les deuxième et troisième chapitres, nous proposons une analyse détaillée de l’évolution du bruit observé en fonction de la fréquence, de la polarisation, et de la géométrie sur des HEMTs des deux familles technologiques SiGe et GaN. Nous avons en particulier étudié les deux générateurs de bruit en courant en entrée et en sortie respectivement iG et iD ainsi que leur corrélation. Ceci nous a permis, en nous appuyant aussi sur l’analyse des caractéristiques statiques des transistors, d’identifier les diverses sources de bruit en excès présentes dans ces composants et de faire des hypothèses sur leurs origines. Le dernier chapitre est consacré aux TBHs à base de SiGe. Dans une première partie nous établissons comment varie le bruit basse fréquence de TBHs, fabriqués par un premier constructeur, en fonction de la polarisation, de la géométrie et de la fraction molaire de germanium. Dans une seconde partie nous mettons en évidence, d’après nos observations effectuées sur des TBHs fabriqués par un second constructeur, l’impact important sur le bruit BF de stress thermiques appliqués sur ce type de composants
This thesis deals mainly with electrical noise in microwave silicon germanium (SiGe) and gallium nitride (GaN) field effect transistors (HEMT’s) and SiGe heterojunction bipolar transistors (HBT’s). The organisation of this memory is as follows, in first chapter, we remember the important properties of excess noise sources encountered in these type devices. In addition, we describe the measurement set-ups used for static and noise characterization. In the second and third chapters, a thoroughful analysis of the noise dependence on frequency, bias, and geometry of both SiGe and GaN HEMT’s, has been carried out, specifically, the input and output current noise sources respectively iG and iD and their correlation. This in combination with static characterization, allowed to identify the different noise sources present in these devices and their supposed origin. .

High frequency data (HFD) of three site studies in different geographic locations were analyzed to reproduce the power spectrum illustrated by Van der Hoven in 1957. His work represents the basis of wind energy standards such as averaging and variability in the frequency domain. The results presented in this thesis unveil discrepancies with Van der Hoven’s approach. A major eddy-energy peak is illustrated at a period of 2 days and a smaller eddy-energy peak contribution at frequencies higher than the region known as the spectrum gap. The variance in the microscale region was calculated by integrating the Power Spectral Density (PSD) over the corresponding range of frequencies. The economic value of this energy variance based on the turbulence kinetic energy of the wind data set is calculated. It is also concluded that, given the results of the study, HFD analysis in the frequency domain uncovers eddy-energy peaks that determine energy fluctuations in the short and long terms. An algorithm was developed to detect delay times in the turbulence kinetic energy (TKE) and the energy dissipation rate ε on a continuous basis (thereby identifying the highest cross-correlation coefficients between them). The Kolmogorov turbulence order is applied to calculate the energy dissipation rate ε through the identification of the inertial subrange. The time scale in the variations of both parameters was successfully calculated and it is close to the time the air takes to circulate between the surface and the top of the atmosphere’s mixed layer. High correlation coefficients are found in the three site studies from 4am to 8am, and from 8pm to 12pm. The cross-correlation function also determines delay time scales in the range of 10-20 minutes and approximately 2 hours. The energy dissipation rate can be calculated to characterize wind variability in a particular site that might affect the performance of a wind turbine. With these results, more information is generated that can be used in the wind turbine’s control system routines to improve its response under wind turbulence variations.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

This thesis examines converter topologies suitable for Module Integrated Converters (MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to the development of the MIC topologies based on the two-inductor boost converter, which has received less research interest than other well known converters. The thesis provides a detailed analysis of the resonant two-inductor boost converter in the MIC implementations with intermediate constant DC links. Under variable frequency control, this converter is able to operate with a variable DC gain while maintaining the resonant condition. A similar study is also provided for the resonant two-inductor boost converter with the voltage clamp, which aims to increase the output voltage range while reducing the switch voltage stress. An operating point with minimized power loss can be also established under the fixed load condition. Both the hard-switched and the soft-switched current fed two-inductor boost converters are developed for the MIC implementations with unfolding stages. Nondissipative snubbers and a resonant transition gate drive circuit are respectively employed in the two converters to minimize the power loss. The simulation study of a frequency-changer-based two-inductor boost converter is also provided. This converter features a small non-polarised capacitor in a second phase output to provide the power balance in single phase inverter applications. Four magnetic integration solutions for the two-inductor boost converter have also been presented and they are promising in reducing the converter size and power loss.

Graphene has the highest mobility of any material at room temperature; this property has attracted a great deal of interest for applications in high frequency electronics, specifically transistors and diodes. To date, there has been little success using graphene for these purposes because it lacks the bandgap necessary to create an efficient device. This work aims to approach this problem from a different angle; using device architecture that potentially does not need a bandgap. This could allow graphene's excellent electrical properties to be exploited fully. The first example of this is the ballistic rectifier; a device that exploits the long mean free path of two dimensional electron gasses so that carriers can be treated like "billiard balls". Here we demonstrate two different four-terminal ballistic rectifiers that redirect carriers from the two input leads to one of the two output leads; the effect of this is to rectify an AC signal into a DC signal. An extremely high voltage responsivity of 23,000 V/W and a very low noise equivalent power of 0.64 pW/Hz1/2 are achieved from a low-frequency AC signal at room temperature. This same device has been tested at 220GHz and showed no signs of a cut-off frequency. Another rectifier tested here is the self-switching diode, a device that uses two side gates attached to its own source to locally gate its own conducting channel. This architecture demonstrates a modest peak responsivity of 690 V/W, a result of graphene's missing bandgap. A side-gated transistor with a modest on/off ratio of ~2.33 is also fabricated in order to better understand the limited capabilities of the graphene self-switching diode. Part of the novelty of this work is the introduction of a modified stamp transfer technique that allowed more flexibility creating hetero-structures. A dry etching recipe for hetero-structures is introduced that does not damage soft masks allowing for a new type of ultra-clean 1D contact. This new contact demonstrates considerably better contact resistance and reliability than previous generations; important for any high frequency application.

Small size, light weight, high efficacy, longer lifetime and controllable output are the main advantages of high-frequency electronic ballasts for gas discharge lamps. However, power line quality and electromagnetic interference (EMI) issues arise when a simple peak rectifying circuit is used. To suppress harmonic currents and improve power factor, input-current-shaping (ICS) or power-factor-correction (PFC) techniques are necessary. This dissertation addresses advanced high-frequency electronic ballasting techniques by using a single-stage PFC approach. The proposed techniques include single-stage boost-derived PFC electronic ballasts with voltage-divider-rectifier front ends, single-stage PFC electronic ballasts with wide range dimming controls, single-stage charge-pump PFC electronic ballasts with lamp voltage feedback, and self-oscillating single-stage PFC electronic ballasts. Single-stage boost-derived PFC electronic ballasts with voltage-divider-rectifier front ends are developed to solve the problem imposed by the high boost conversion ratio required by commonly used boost-derived PFC electronic ballast. Two circuit implementations are proposed, analyzed and verified by experimental results. Due to the interaction between the PFC stage and the inverter stage, extremely high bus-voltage stress may exist during dimming operation. To reduce the bus voltage and achieve a wide-range dimming control, a novel PFC electronic ballast with asymmetrical duty-ratio control is proposed. Experimental results show that wide stable dimming operation is achieved with constant switching frequency. Charge-pump (CP) PFC techniques utilize a high-frequency current source (CS) or voltage source (VS) or both to charge and discharge the so-called charge-pump capacitor in order to achieve PFC. The bulky DCM boost inductor is eliminated so that this family of PFC circuits has the potential for low cost and small size. A family of CPPFC electronic ballasts is investigated. A novel VSCS-CPPFC electronic ballast with lamp-voltage feedback is proposed to reduce the bus-voltage stress. This family of CPPFC electronic ballasts are implemented and evaluated, and verified by experimental results. To further reduce the cost and size, a self-oscillating technique is applied to the CPPFC electronic ballast. Novel winding voltage modulation and current injection concepts are proposed to modulate the switching frequency. Experimental results show that the self-oscillating CS-CPPFC electronic ballast with current injection offers a more cost-effective solution for non-dimming electronic ballast applications.
Ph. D.

Silicon Germanium BiCMOS technology has been demonstrated as an ideal platform for highly integrated systems requiring both high performance analog and RF circuits as well as large-scale digital functionality. Frequency synthesizers are ideal candidates for this technology because the mixed-signal nature of modern frequency synthesis designs fundamentally requires both digital and analog signal processing. This research targets three areas to improve SiGe frequency synthesizers. A majority of this work focuses on applying SiGe frequency synthesizers to extreme environment applications such as space, where low temperatures and ionizing radiation are significant design issues to contend with. A second focus area involves using SiGe HBTs to minimize noise in frequency synthesizer circuits. Improved low frequency "pink" noise in SiGe HBTs provide a significant advantage over CMOS devices, and frequency synthesis circuits are significantly affected by this type of noise. However, improving thermal "white" noise is also considered. Finally, an analysis of AM-PM distortion is considered for SiGe HBTs. The studies presented focus on identifying the physical mechanisms of observed phenomena, such as single event transients or phase noise characteristics in oscillators. The ultimate goal of this research is to provide a reference of effective design parameters for circuit and system designers seeking to take advantage of the properties of SiGe device physics.

Since its invention in 1885 by Otto Bláthy, Miksa Déri and KárolyZipernowsky, transformers have become an important cornerstone of theelectrical infrastructure we have today. They are found mostprominently in any machinery or device that requires a differentlevel of voltage or current than a general grid can supply, such ascomputers, motors or even cars. In the case of this project, thetransformer was originally intended to be connected to a resonatingH-bridge which supplies the primary coil with high frequency voltagepulses to be converted into a higher voltage transferred to arectifier unit. Because of the level of frequency supplied, thetransformer was required to be constructed with a different type ofcore and cable for the winding. When it became clear that the cablecouldn't be supplied in time, the focus shifted towards constructinga prototype instead. The prototype was designed to generate a certainamount of leakage inductance while subjected to a short circuit test.After a couple of attempts, the group managed to construct atransformer whose leakage inductance was well within range of thespecifications. The finished transformer prototype was delivered andthe group had thus successfully constructed what is to be used as atemplate for further transformers of the same type.A special thanks to ScandiNova Systems AB for initiating this projectand giving us the opportunity to participate, and to Per Nilsson, PerBenkowski and Klas Elmqvist for mentoring us along the way.

This thesis discusses the development, characterisation and evaluation of a compact, medium power, XeCl laser operating at pulse repetition frequencies (prf) >1kHz. The use of this laser to cut polymer films by ablative etching is also presented. The device uses a closed-cycle gas flow loop, constructed from stainless-steel for corrosive gas compatibility, and a total volume of 6 litres and a working pressure of 4 atmospheres. A magnetically coupled, tangential fan provides the gas flow and, with appropriate flow shaping into the 0.8 x 1.5 x 22.0cm⁻³ discharge region, produces a maximum flow velocity of 40m.s⁻¹. Electrical excitation is provided by a conventional, thyratron switched, capacitor discharge circuit, coupled with an internal, capacitively loaded, uv spark preionisation scheme, resulting in a rapid energy deposition into the discharge. Investigations of the effects of discharge perturbations on the maximum repetition rate capability of this laser, Indicate that repetition rates up to 1800Hz should be feasible. In operation, the laser has proven to be capable of 16W at 1kHz, and 22W at 700Hz, with a 10nF charging capacitor. Qualitative studies of the effect of resonator configuration on the beam profile, have shown that the use of folded cavities will produce more uniform beam profiles. Experiments have been carried out, using this laser, to cut thin polyethylene teraphthalate (PET) film at rates up to 1.3m.s⁻¹. The 8x15mm output beam from the laser, was brought to a 5.4mm long line-focus with a full width of 140µm. It is shown that the effective etch rate, and corresponding cutting efficiency, is markedly dependent on prf due, it Is thought, to cumulative heating.

In recent years, problems relating to the analysis of data streams have become widespread. A data stream is a collection of time ordered observations x1, x2, ... generated from the random variables X1, X2, .... It is assumed that the observations are univariate and independent, and that they arrive in discrete time. Unlike traditional sequential analysis problems considered by statisticians, the size of a data stream is not assumed to be fixed, and new observations may be received over time. The rate at which these observations are received can be very high, perhaps several thousand every second. Therefore computational efficiency is very important, and methods used for analysis must be able to cope with potentially huge data sets. This paper is concerned with the task of detecting whether a data stream contains a change point, and extends traditional methods for sequential change detection to the streaming context. We focus on two different settings of the change point problem. The first is nonparametric change detection where, in contrast to most of the existing literature, we assume that nothing is known about either the pre- or post-change stream distribution. The task is then to detect a change from an unknown base distribution F0 to an unknown distribution F1. Further, we impose the constraint that change detection methods must have a bounded rate of false positives, which is important when it comes to assessing the significance of discovered change points. It is this constraint which makes the nonparametric problem difficult. We present several novel methods for this problem, and compare their performance via extensive experimental analysis. The second strand of our research is Bernoulli change detection, with application to streaming classification. In this setting, we assume a parametric form for the stream distribution, but one where both the pre- and post-change parameters are unknown. The task is again to detect changes, while having a control on the rate of false positives. After developing two different methods for tackling the pure Bernoulli change detection task, we then show how our approach can be deployed in streaming classification applications. Here, the goal is to classify objects into one of several categories. In the streaming case, the optimal classification rule can change over time, and classification techniques which are not able to adapt to these changes will suffer performance degradation. We show that by focusing only on the frequency of errors produced by the classifier, we can treat this as a Bernoulli change detection problem, and again perform extensive experimental analysis to show the value of our methods.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 72-74).
Miniaturization of power electronics can improve the performance of many applications, such as renewable energy systems, data centers, and aerospace systems. Operation in the high frequency (HF) regime (3{ 30 MHz) has potential for miniaturizing power electronics, but designing small, efficient inductors at HF can be challenging. At these frequencies, losses due to skin and proximity effects are difficult to reduce, and gaps needed to keep B fields low in the core add fringing field loss. This thesis aims to improve the design of HF inductors. A low-loss inductor structure for HF applications and associated design guidelines that optimize for loss have been developed. The structure achieves low loss through quasi-distributed gaps and a new field shaping technique that achieves low winding loss through double-sided conduction. An example ~15 [mu]H inductor designed using the proposed guidelines achieved an experimental quality factor of 720 at 3MHz and 2A (peak) of ac current.
In some cases, litz wire may further improve the performance of the proposed structure. With litz wire, the example inductor achieved an improved quality factor of 980. The proposed structure also has great design and application flexibility. Core sets for this structure can be scaled by a factor-of-four in volume and still cover a large, continuous range of inductor requirements, e.g. power handling and inductances. A wide range of requirements can therefore be achieved with a small set of core pieces. The proposed inductor structure and design techniques thus have greater potential for commercial adoption to facilitate the design of low-loss HF inductors. The design techniques used in the proposed structure can also be extended to high-power radio-frequency (RF) applications, such as RF power amplifiers for industrial plasma generation. A modified version of the proposed structure, along with modified design guidelines, can achieve low loss in this operating space.
Simulations show that an example ~600 nH inductor achieves a quality factor of 1900 at 13:56MHz and 78A (peak). Therefore, the developed design techniques and inductor structures are suitable for small, highly-efficient inductors at HF, and can thereby help realize high-frequency miniaturization of power electronics.
by Rachel S. Yang.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

Il presente lavoro e’ stato svolto in cooperation tra l’infineon e l’Universita’ Milano Bicocca, l’obbiettivo e’ sviluppare il cuore di un convertitore DC-DC Buck Converter ad alta frequenza di commutazione. I convertitori a commutazione offrono un modo semplice ed efficiente per alimentare carichi elettronici. Inoltre, gli alimentatori DC-DC consentono di soddisfare efficacemente molti requisiti di sicurezza delle automobili moderne. Ad esempio è assolutamente necessario che le luci di emergenza, i fari e le luci dei freni mantengano la loro funzionalità in tutte le condizioni, soprattutto durante l'avviamento a freddo, quando la tensione della batteria raggiunge valori molto bassi (anche 4V). Ma in certe condizioni esperimentano tensioni anche superiori ai 30V. Gli alimentatori DC-DC ben si adattano ad ampie e repentine variazioni della tensione di alimentazione, inoltre alla loro relativa semplicità uniscono un’alta efficienza, valori superiori al 90%. Aumentando la frequenza di commutazione si riducono linearmente le dimensioni dei componenti reattivi, permettendo schede PCB più piccole e conseguentemente costi ridotti. Le tecnologie BCD consentono di integrare su un singolo chip (SOC - System On Chip) transistor di potenza, logica di controllo e diagnostica. In questa ricerca sono stati sviluppati tre convertitori Buck che lavorano a tre diverse frequenze 1MHz, 4MHz e 10MHz con una corrente di uscita di 3A. Tra i Buck converter disponibili sul mercato solo quelli più performanti hanno frequenze di commutazione di 2,0-2,5 MHz e correnti nel carico di 2-2,5 A. Poiché l'obiettivo di 10MHz con una corrente di carico di 3A è molto aggressivo, è stata adottata un'architettura del convertitore Buck che minimizza il tempo di transizione dei segnali elettrici ed è stato necessario sviluppare una nuova topologia di driver molto più veloce e potente delle soluzioni adottate finora (patent pending). Al momento in cui scriviamo, i dispositivi da 1 MHz e 4 MHz sono in fase di diffusione. L'uscita dei wafer è prevista per febbraio 2023. Il terzo convertitore Buck (10 MHz) e’ in attesa di diffusione. Durante questo lavoro di dottorato sono state presentate quattro proposte di brevetto.
This work was carried out in cooperation between Infineon and the University of Milan Bicocca, the aim being to develop the core of a DC-DC Buck Converter with a high switching frequency. Switching converters offer a simple and efficient way to power electronic loads. In addition, DC-DC power supplies make it possible to effectively meet many safety requirements of modern automobiles. For example, it is absolutely necessary that emergency lights, headlights and brake lights maintain their functionality under all conditions, especially during cold starting, when the battery voltage reaches very low values (even 4V). But under certain conditions they experience voltages even above 30V. DC-DC power supplies are well suited to large and sudden variations in supply voltage, and in addition to their relative simplicity they combine high efficiency, values of over 90%. Increasing the switching frequency reduces the size of reactive components linearly, allowing smaller PCBs and consequently lower costs. BCD technologies allow power transistors, control logic and diagnostics to be integrated on a single chip (SOC - System On Chip). In this research, three Buck converters were developed that operate at three different frequencies 1MHz, 4MHz and 10MHz with an output current of 3A. Of the buck converters available on the market, only the best performing ones have switching frequencies of 2.0-2.5MHz and load currents of 2-2.5A. Since the target of 10MHz with a load current of 3A is very aggressive, a Buck converter architecture was adopted that minimises the transition time of electrical signals, and a new driver topology had to be developed that is much faster and more powerful than the solutions adopted so far (patent pending). At the time of writing, 1 MHz and 4 MHz devices are being deployed. The wafers are scheduled for release in February 2023. The third Buck converter (10 MHz) is pending deployment. Four patent proposals were submitted during this doctoral work.

Mechanical Engineering
M.S.M.E.
Magnets play a major role in our rapidly developing world of technology. Electric motors and generators, transformers, data storage devices, MRI machines, cellphones, and NMR are some of the many applications for magnets. However, almost all the magnets currently being used have rare-earth heavy metals in them. Despite their high-energy product, the presence of rare-earth metals increases the cost significantly. Also, the processes involved in the mining of rare-earth metals are hazardous to the environment, and to all life forms. In the past few decades, oxide based magnets have gained a lot of attention as potential replacements for the rare-earth magnets. Oxide based magnetic nanocrystals are attracting a lot of attention as a potential replacement for rare-earth magnets. They are stable in ambient condition and their manufacturing cost is very low when compared to the rare-earth magnets. My work deals with the synthesis of core-shell magnetic structure for high frequency applications (Chapter 1) and the synthesis of high energy product magnetic nanocrystals (Chapter 2) and the synthesis of soft magnetic nanocrystals for high frequency measurement. NiZn ferrite, a soft oxide based magnet cannot be directly implied at high frequencies as they fail at the frequency which over the MHz range. On the other hand, BaZn ferrite is a Y-type magnets, which is robust at higher frequencies. Therefore, using the latter magnet as a protective shell for core material, made of former magnet, enables us to manufacture a cheap solution to the rare-earth magnets used in our cell phones and other devices that work on high frequency signals. On the other hand, successful coating of a very soft magnetic material on a hard-magnetic core increases the total energy product of the magnetic composite, which enhances its versatility.
Temple University--Theses