Dissertations / Theses on the topic 'Steady State Frequency'

Oscillator circuits are an integral component of wireless communications systems and are increasingly in demand. As such systems gain widespread use, price becomes a very important factor in the design process, and the design cycle must be optimized. This puts an increasing emphasis on the proficiency of oscillator design automation tools. At the same time, as the performance requirements of such systems are becoming more stringent, the required simulation complexity is also increasing. More specifically, high frequency selectivity and low phase noise require very high quality factor oscillators, which in turn negatively affect the convergence performance of current simulation techniques. This thesis proposes a new continuation method for improving the convergence of oscillator simulations and compares this method to some of the methods reported in the literature. The proposed approach does not require a very good initial guess in order to converge to a final solution.

This thesis suggests a Bayesian vector autoregressive (VAR) model which allows for explicit parametrization of the unconditional mean for data measured at different frequencies, without the need to aggregate data to the lowest common frequency. Using a normal prior for the steady-state and a normal-inverse Wishart prior for the dynamics and error covariance, a Gibbs sampler is proposed to sample the posterior distribution. A forecast study is performed using monthly and quarterly data for the US macroeconomy between 1964 and 2008. The proposed model is compared to a steady-state Bayesian VAR model estimated on data aggregated to quarterly frequency and a quarterly least squares VAR with standard parametrization. Forecasts are evaluated using root mean squared errors and the log-determinant of the forecast error covariance matrix. The results indicate that the inclusion of monthly data improves the accuracy of quarterly forecasts of monthly variables for horizons up to a year. For quarterly variables the one and two quarter forecasts are improved when using monthly data.

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.

The modern electric power systems are going through significant changes because of continuous increasing demand of electric power. Further, a growing number of renewable energy systems that directly deliver DC power jointly considered with the advance in DC technology allows a more efficient and affordable use of energy. Furthermore, a rising use of DC systems and microgrids in a wide number of applications has motivated the study of Power Quality (PQ). The concept of power quality in DC systems and microgrids brings many challenges and the aim of this thesis is to understand the delivered power quality in DC microgrid systems. In this thesis, the effects of low frequency range (0-2 kHz) conducted emissions on power quality from a microgrid based DC/DC converter under steady state and transient loading conditions represent the main purpose of this work. Indeed, for a DC distribution network there is a lack of standards and guidelines concerning power quality issues and acceptable levels of conducted disturbances in the aforementioned frequency range. Consequently, the objective of this thesis is to quantify adequate power quality indices for DC systems or networks with connected loads such as Low Frequency Sinusoidal Disturbance (% LFSD) and Amplitude Probability Distribution (APD) indices.

Introduction

Les surdités cochléaires induisent, outre une audibilité réduite, une série de distorsions de la représentation neurale des sons. Deux des mécanismes à la base de ces distorsions sont d’une part une atteinte de la sélectivité fréquentielle et d’autre part des zones neuro-épithéliales non fonctionnelles. Tant le premier que le second mécanisme apparaissent dans une proportion variable et non prédictible d’un sujet à un autre. Deux tests permettent le diagnostic de ces atteintes spécifiques: la Courbe d’Accord (Tuning Curve: TC) et le Threshold Equalising Noise (TEN) test. La TC, mesurée par une technique psychoacoustique chez un adulte collaborant (Psychophysical TC: PTC), consiste en la mesure du niveau de bruit (masqueur) nécessaire pour masquer un son pur (signal) de fréquence et d’intensité fixes. Le TEN test consiste en la mesure des seuils auditifs dans le silence et en présence d’un bruit égalisateur de seuil (TEN). Ces tests qui requièrent des capacités cognitives adultes normales, ne sont pas applicables aux populations pédiatriques prélinguales.

Ce travail de thèse avait pour but le développement d’un équivalent objectif et non invasif des TCs et du TEN test applicable aux populations pédiatriques. La méthode objective choisie fut les potentiels auditifs stationnaires ou ASSEPs (Auditory Steady State Evoked Potentials). Les ASSEPs sont une réponse électrophysiologique cérébrale évoquée par un stimulus acoustique de longue durée modulé en amplitude et/ou en fréquence.

Méthodes & Résultats

Etape 1

Les développements méthodologiques ont été réalisés sur l’espèce canine et humaine adulte. Les ASSEPs n’ayant jamais été préalablement enregistrés chez le chien, une première étape à consister à définir chez cette espèce les paramètres d’enregistrement optimaux (modulation en amplitude optimale) dont on sait qu’ils interagissent avec l’état veille-sommeil, avec la fréquence testée et probablement avec l’espèce animale investiguée.

A cette fin, les seuils auditifs obtenus chez 32 chiens à l’aide des ASSEPs ont été validés à cinq fréquences audiométriques par comparaison aux seuils obtenus avec les potentiels auditifs du tronc cérébral évoqués aux bouffées tonales.

Les seuils obtenus aux ASSEPs avec les paramètres optimaux d’enregistrement (légèrement différents des paramètres optimaux humains) étaient similaires à ceux obtenus aux bouffées tonales.

Ces résultats ont été publiés dans Clinical Neurophysiology (Markessis et al. 2006; 117: 1760-1771).

Etape 2

La possibilité de mesurer des TCs à l’aide des ASSEPs (ASSEP-TCs) a été évaluée sur 10 chiens. Les données canines ont été comparées à des données de la littérature, çàd aux TC enregistrées chez d’autres espèces et avec d’autres méthodes. Des ASSEP-TCs ont également été enregistrées chez 7 humains adultes et confrontées aux PTCs obtenues chez les mêmes sujets. Les PTCs sont typiquement energistrées avec un signal sinusoïdal alors que le stimulus utilisé pour évoquer un ASSEP est une sinusoïde modulée en amplitude. L’effet des sinusoïdes modulées en amplitude sur les paramètres qualitatifs et quantitatifs des TCs a donc été évalué en comparant les PTCs obtenues avec un son pur et avec un son pur modulé en amplitude chez 10 humains adultes.

Les résultats ont révélé que les ASSEP-TCs enregistrées chez le chien et l’humain présentaient des paramètres qualitatifs et quantitatifs similaires respectivement à ceux décrits dans la littérature et aux PTCs. Par ailleurs, auncun effet des stimuli modulés en amplitude sur les paramètres des PTCs n’a été démontré.

Ces données ont été publiées dans Ear & Hearing (Markessis et al. 2009, 30: 43-53).

Etape 3

Les ASSEP-TCs ont été validées chez 10 chiens en comparant les données aux TC enregistrées par électrocochléographie (Compound Action Potential TC: CAP-TC). Le masqueur utilisé pour les CAP-TCs est typiquement une sinusoïde alors que le masqueur utilisé pour les ASSEP-TCs est un bruit à bande étroite. Dès lors, une comparaison du type de masqueur (sinusoïde vs bruit à bande étroite) sur les paramètres des CAP-TCs et ASSEP-TCs a été réalisée chez 10 chiens.

Les ASSEP-TCs chez le chien se sont révélées qualitativement et quantitativement similaires aux CAP-TCs quel que soit le type de masqueur. Elles presentaient par ailleurs l’avantage d’être moins variables, plus précises et non invasives par rapport aux CAP-TCs.

Ces données ont été publiées dans International Journal of Audiology (Markessis et al. 2010, 49 ;455-62).

Etape 4

Afin d’étudier la validité de la procédure à mettre en évidence des changements de sélectivité fréquentielle dus à une atteinte cochléaire, des ASSEP-TCs ont été obtenues chez 10 chiens cochléo-lésés suite à un trauma acoustique. Les Produits de Distorsion Acoustiques, les potentiels évoqués auditifs du tronc cérébral évoqués par un clic et les ASSEPs à cinq fréquences audiométriques ont été enregisrés afin de délimiter l’étendue de la lésion.

Les ASSEP-TCs ont été fortement altérées, mais pas comme attendu ni suggéré par les mesures fonctionnelles indiquant que le trauma acoustique a créé une lésion différente de celle espérée.

Cette étude doit être poursuivie, des lésions moins importantes créées et une validation histopathologique réalisée.

Etape 5

Le TEN test a été mesuré à l’aide des ASSEPs (ASSEP-TEN) chez 12 adultes et cinq enfants normo-entendants. Les données adultes ont été confrontées aux données comportementales. L’effet des stimuli ASSEP (son pur modulé en amplitude) sur les TEN test a également été investigué en comparant les données comportementales obtenues avec une sinusoïde et avec une sinusoïde modulée en amplitude chez 24 adultes.

Les seuils masqués enregistrés aux ASSEPs étaient supérieurs à ceux mesurés par une épreuve comportementale. L’élévation des seuils masqués pose un problème potentiel de dynamique.

La procédure doit être testée chez des patients présentant une surdité cochléaire attendu que la différence entre les seuils auditifs mesurés aux ASSEPs et par une épreuve comportementale est moindre dans cette population. Dans la mesure où le problème de dynamique résiduelle persiste chez les patients malentendants, d’autres stimuli ou algorithmes d’enregistrement doivent être utilisés.

Etape 6

Le TEN est un stimulus large bande. Il peut dès lors se révéler intolérable chez des patients présentant une atteinte auditive restreinte à une region fréquentielle. L’effet du filtrage du TEN sur les seuils et la sonie du TEN a été étudié chez 24 sujets normo-entendants et 35 patients présentant une perte cochléaire dans les hautes fréquences.

Le filtrage passe-haut du TEN s’est avéré être une solution satisfaisante.

Ces données ont été publiées dans International Journal of Audiology (Markessis et al. 2006; 45: 91-98).

Etape 7

L’effet de l’intensité du TEN sur le diagnostic des zones neuro-épithéliales non fonctionnelles a été investigué chez 24 patients en mesurant les seuils masqués à quatre intensités de TEN différentes. La fiabilité du TEN test a également été évaluée.

Le TEN est une procédure fiable. L’intensité du TEN a affecté le diagnostic chez cinq patients. Ce résultat est interprété en termes de degré de l’atteinte du complexe neurosensoriel.

Ces données ont été publiées dans International Journal of Audiology (Markessis et al. 2009; 48: 55-62).

Conclusion

Un algorithme permettant la mesure de TC et du TEN test objective à l’aide des ASSEPs a été développé. L’implémentation clinique de l’algorithme appliqué à l’enregistrement des CA paraît envisageable. Une importante étape de la corrélation entre modifications anatomiques (à l’aide de l’histopathologie) et physiologiques (ASSEP-TC et CAP-TC) est maintenant celle qui s’impose. Les données préliminaires obtenues sur le TEN test électrophysiologique chez des sujets normo-entendants suggèrent que son implémentation clinique puisse se heurter à un problème de dynamique si ce dernier est confirmé en présence de surdités cochléaires. Plusieurs pistes potentielles de solutions ont été avancées.

Doctorat en Sciences biomédicales et pharmaceutiques
info:eu-repo/semantics/nonPublished

A differential, membrane-based nanocalorimeter has been designed and constructed for thermal studies of mesoscopic samples at low temperatures. The calorimeter is intended for sample masses from mg to sub-μg and a broad temperature range from above room temperature down to the sub-K region. It allows concurrent use of ac steady state and relaxation methods. Effort was spent to achieve good absolute accuracy to enable investigations of the electronic contribution to the heat capacity of superconductors. The calorimeter consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: i) The resistive thermometer, made of a GeAu alloy, displays a high sensitivity, dlnR/dlnT ≈ −1 over the entire temperature range. ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. iv) Absolute accuracy is achieved via a novel variable-frequency fixed-phase technique in which the measurement frequency is automatically adjusted during ac-calorimetry measurements to account for the temperature variation of the sample specific heat and the device thermal conductance. The properties of the empty cell and the effect of the thermal link between sample and cell were analytically studied. Practical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation amplitude of the system were formulated. Comparisons with measurements and numerical simulations show excellent agreement. Calibration procedures are simple, but care should be taken to minimize thermal radiation effects. The experimental setup is operated with self-regulation of heater powers and thermometer bias, including compensation to zero the differential dc signal. As a result its high resolution and compact format, the calorimeter is well suited for studies of phase transitions and phase diagrams as well as electronic specific heat. The performance of the device is demonstrated by a study of the superconducting state of a small lead crystal.
En differentiell, membran-baserad nanocalorimeter har designats och tillverkats för termiska studier av mesoskopiska prover vid låg temperatur. Kalorimetern är avsedd för provmassor från mg till sub-μg och ett brett temperaturområde från över rumstemperatur till under 1 K. Den tillåter samtidig användning av både ac steady state och relaxations-metod. Fokus har lagts på att uppnå en god absolut noggrannhet för att möjliggöra studier av det elektroniska bidraget till värmekapaciteten hos supraledare. Kalorimetern består av två celler, var och en uppbyggd som en stack med värmeelement och termometer i mitten av ett kiselnitrid-membran, med en total bakgrundsvärmekapacitet på mindre än 100 nJ/K vid 300 K, minskande till 10 pJ/K vid 1 K. Kalorimetern har flera särdrag: i) Den resistiva termometern, gjord av en GeAu legering, visar en hög känslighet, dlnR/dlnT ≈ −1 över hela temperaturområdet. ii) Provet placeras i direkt kontakt med termometern, som tillåts att självvärma. Termometern kan alltså användas vid hög dc ström för att öka upplösningen. iii) Mätningarna genomförs med en uppsättning av åtta synkroniserade lock-in förstärkare, som mäter dc, grundfrekvens och 1:a övertonen hos värme-element och termometer. iv) Absolut noggrannhet uppnås genom en ny variabel-frekvens konstant-fas teknik där mätfrekvensen justeras automatiskt under ac-kalorimetrimätningar för att kompensera temperaturberoendet hos provets specifika värmekapacitet och kalorimetercellens värmeledningsförmåga. Egenskaperna hos den tomma cellen och inverkan av den termiska länken mellan prov och cell studerades analytiskt. Praktiska uttryck för att beskriva frekvens beroendet hos systemets värmekapacitet, värmeledningsförmåga, och temperaturoscillationer har formulerats. Jämförelser mellan mätningar och numeriska simuleringar visar mycket bra överensstämmelse. Kalibreringsförfarandet är enkelt, men försiktighet bör vidtas för att minimera värmestrålningseffekter. Experimentuppställningen drivs med självreglering av värmare och termometer, inklusive kompensation för att nollställa den differentiella dc signalen. Som en följd av dess höga upplösning och kompakta format är kalorimetern väl lämpad för studier av fasövergångar och fasdiagram såväl som det elektroniska specifika värmet. Kalorimeterns prestanda demonstreras genom en studie av det supraledande tillståndet hos en liten blykristall.
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Accepted.

L'électronique de puissance vise à conditionner et contrôler l'énergie d'une source vers une charge. Les convertisseurs de puissance, tels que les convertisseurs DC-DC, génèrent une tension de sortie stable à partir d'une tension d'entrée non stable. Dans la quête de miniaturisation et d'augmentation de la densité de puissance, l'utilisation d'un élément piézoélectrique pour le stockage d'énergie mécanique offre des perspectives prometteuses, notamment à des fréquences de l'ordre du MHz.La thèse vise à contribuer au domaine des convertisseurs DC-DC utilisant des résonateurs piézoélectriques pour stocker l'énergie mécaniquement. L'objectif est de proposer des stratégies de régulation et un circuit intégré pour les convertisseurs DC-DC piézoélectriques non isolés fonctionnant à plusieurs MHz. Ces convertisseurs présentent un intérêt majeur en éliminant le composant magnétique traditionnel, favorisant ainsi la miniaturisation et l'augmentation de la densité de puissance. Le manque de régulation à haute fréquence constitue une lacune que la thèse s'efforce de combler.Cette thèse présente des convertisseurs DC-DC piézoélectrique, mettant en évidence son importance pour accroître la densité de puissance. L'état de l'art de ces convertisseurs est exploré, réalisant une comparaison objective des performances entre les topologies existantes. Nous introduisons un modèle théorique générique pour toutes les topologies de convertisseurs DC-DC piézoélectriques, apportant une avancée significative dans la prédiction de la fréquence d'opération, de la durée de chaque phase du cycle de conversion et de l'amplitude maximale du courant piézoélectrique en fonction de la puissance transmise et du résonateur piézoélectrique utilisé. Une étude d'optimisation de ces convertisseurs est également menée dans le but de définir la fréquence de fonctionnement optimale (le résonateur piézoélectrique à utiliser) et la topologie optimale à mettre en œuvre pour maximiser la densité de puissance tout en minimisant les pertes, pour une tension d'entrée, un rapport de conversion et une puissance de sortie donnés.Dans ce manuscrit il est présenté une stratégie de régulation à une fréquence d'environ 10 MHz basée sur cinq boucles de contrôle fonctionnant en parallèle. La validation de cette stratégie est discutée, mettant en lumière les défis liés aux simulations. Nous présentons le processus de conception analogique des principaux blocs de chaque boucle de régulation, ainsi que sur deux étages de puissance optimisés pour différentes puissances de sortie en technologie XFAB06. Il est également présenté le layout final du convertisseur conçu et les simulations avec des variations de fabrication liés au circuit intégré et de température. Des résultats réalistes sont obtenus, démontrant le bon fonctionnement du convertisseur à environ 10, 6 et 1 MHz.Les prochaines étapes impliquent des mesures expérimentales sur le circuit intégré conçu, une étude théorique approfondie des boucles de régulation pour différentes topologies, et l'exploration de solutions telles qu'un FPGA pour une régulation à environ 10 MHz. La recherche vise à renforcer la robustesse et la flexibilité des convertisseurs DC-DC piézoélectriques non isolés, ouvrant la voie à des applications plus diversifiées et efficaces au-delà du MHz. En résumé, cette thèse constitue une première preuve de concept pour le développement de convertisseurs piézoélectriques plus robustes en termes de densité de puissance, de faible rayonnement électromagnétique et de compacité du résonateur piézoélectrique
Power electronics aims to condition and control energy from a source to a load. Power converters, such as DC-DC converters, generate a stable output voltage from an unstable input voltage. In the pursuit of miniaturization and increased power density, the use of a piezoelectric element for mechanical energy storage holds promising prospects, especially at frequencies on the order of MHz.The thesis aims to contribute to the field of DC-DC converters using piezoelectric resonators for mechanical energy storage. The goal is to propose regulation strategies and an integrated circuit for non-isolated piezoelectric DC-DC converters operating at multiple MHz. These converters are of significant interest as they eliminate the traditional magnetic component, thus favoring miniaturization and increased power density. The lack of high-frequency regulation is a gap that the thesis strives to fill.This thesis presents piezoelectric DC-DC converters, highlighting their importance in increasing power density. The state of the art of these converters is explored, providing an objective comparison of performance among existing topologies. A generic theoretical model for all piezoelectric DC-DC converter topologies is introduced, representing a significant advance in predicting the operating frequency, duration of each phase of the conversion cycle, and the maximum amplitude of the piezoelectric current as a function of transmitted power and the piezoelectric resonator used. An optimization study of these converters is also conducted to define the optimal operating frequency (the piezoelectric resonator to be used) and the optimal topology to implement, maximizing power density while minimizing losses for a given input voltage, conversion ratio, and output power.In this manuscript, a regulation strategy at a frequency of approximately 10 MHz based on five parallel control loops is presented. The validation of this strategy is discussed, highlighting the challenges related to simulations. The analog design process of the main blocks of each regulation loop is presented, as well as two power stages optimized for different output powers in XFAB06 technology. The final layout of the designed converter and simulations with manufacturing variations related to the integrated circuit and temperature are also presented. Realistic results are obtained, demonstrating the proper operation of the converter at around 10, 6, and 1 MHz.The next steps involve experimental measurements on the designed integrated circuit, a comprehensive theoretical study of regulation loops for different topologies, and the exploration of solutions such as an FPGA for regulation at around 10 MHz. The research aims to strengthen the robustness and flexibility of non-isolated piezoelectric DC-DC converters, paving the way for more diverse and efficient applications beyond the MHz range. In summary, this thesis constitutes an initial proof of concept for the development of more robust piezoelectric converters in terms of power density, low electromagnetic radiation, and compactness of the piezoelectric resonator

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Neste trabalho são propostas duas formulações de importantes ferramentas para análise de redes em regime permanente, onde são consideradas equações que descrevem o comportamento do controle primário e secundário de frequência em sistemas elétricos de potência. A primeira proposta é baseada em uma formulação do problema de fluxo de potência convencional e a segunda uma formulação do fluxo de potência ótimo. A formulação de fluxo de potência proposta é desenvolvida a partir de uma metodologia genérica de representação de dispositivos de controle. Esta metodologia consiste em incorporar as equações que modelam dispositivos de controle ao problema básico de fluxo de potência em coordenadas polares, formando um sistema de equações de ordem (2nb+nc). O fluxo de potência desenvolvido é capaz de estimar os desvios de frequência do sistema devido a uma perturbação da carga. Por outro lado, o fluxo de potência ótimo proposto é capaz de identificar montantes e locais de corte carga, de forma a manter a frequência do sistema em uma faixa aceitável de operação. A formulação proposta de FPO consiste em incluir no problema equações de igualdade e desigualdade associadas com o controle primário de frequência e geração de potência ativa. Os desenvolvimentos propostos para o fluxo de potência convencional foram implementados no ambiente MatLab®. Para solução do fluxo de potência ótimo utilizou-se um pacote comercial de otimização, denominado LINGO®. A avaliação do fluxo de potência e fluxo de potência ótimo propostos é feita através do estudo de sistemas tutoriais e do sistema New England. A validação da análise de desvios de frequência é feita através da utilização do programa ANATEM, desenvolvido pelo CEPEL. Os resultados obtidos mostram as vantagens da utilização das formulações propostas.
This work proposes a new formulation for both the conventional power flow and the optimal power flow formulation, in which the steady-state equations describing the primary and secondary frequency control in electrical power systems are included. The proposed power flow formulation is based on a flexible methodology for the representation of control devices. Such methodology incorporates equations that model control devices into the basic power flow formulation in polar coordinates, generating an augmented system of equations having order (2nb + nc). The developed power flow is able to estimate the system frequency deviation due to a load disturbance. On other hand, the proposed optimum power flow formulation is able to identify the minimum load shedding necessary to maintain the system frequency in an acceptable range of operation. The proposed OPF formulation includes additional equality and inequality constraints to represent the steady state primary frequency control as a function of the active power generation. The proposed development for the conventional power flow was made using the MATLAB® environment. The optimal power flow solution used a commercial optimization package called LINGO®. The evaluation of the proposed power flow and optimal power flow formulations were made through the study of small test systems and the New England test system. Validations of the frequency deviation analysis were made using the program ANATEM, developed by CEPEL. The results obtained show the advantages of using the proposed formulations.

The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

This thesis deals with the analysis, design and test of three-phase high efficiency electrical motors, with particular reference to motors with a rotor winding. At first, the background and the motivations of this work are described. The bibliography on the subjects is deeply examined and a selection of the most relevant papers can be found in the reference. In this scenario, the main objective of this thesis are illustrated. The Line-Start (LS) Synchronous Machine (SyM) design is a subject under investigation since the beginning of the last century, when solid state power converters was not available to drive SyMs. The LS SyM diffusion was limited by the intrinsic difficulties in its design and by the availability of the cheaper and more robust Induction Machine (IM). The working principle of IM and LS SyM are briefly described, as well as the state of the art of the techniques of analysis. Recently, there is a renewed interest on LS SyMs due to the new efficiency requirements and fast analysis techniques are required for the LS SyM design. A Finite-Element (FE) aided analytical model is developed to simulate the LS SyM dynamic. The aim is to develop a model that gives reliable solutions with limited computational efforts compared with other analysis techniques. With this procedure, the LS SyM rotor parameters can be quickly calibrated to fulfill the dynamic load requirements. An innovative analysis technique of LS SyM steady state condition is described. Such an analysis is carried out in the same reference frame used for classical SyMs. It is shown that the analysis can be used to optimize some machine parameters. The issues in LS SyM manufacturing are introduced, with particular reference to the die casting process. The possibility to apply the recent improvements in the SRM design to LS SyM is discussed from the manufacturing point of view. Stochastic optimization has been adopted for the design of electrical motors to reduce the torque ripple, increase the average torque and reduce the losses. The LS SyM torque ripple reduction, achieving at the same time a high average torque, is an important issue even though this topic is not treated extensively in the literature for LS SyM. For this reason, a stochastic optimization is considered in this thesis for the design of a new LS SyM lamination. The analysis is applied on a small size, 2-pole, three-phase LS SyM as this category is still not found in the motor market. The optimization is carried out considering the necessity to achieve a robust design, suitable for the industrial production, as such a LS SyM must be competitive with the workhorse of electrical motors, the IM. One of the most promising design is prototyped. Its performance are compared with the corresponding IM. To demonstrate the feasibility in adopting LS SyM in the large-scale production, an innovative LS SyM design is proposed. The main aim is to use the same lamination for motors of different number of poles so as to reduce the manufacturing cost. A tradeoff between contrasting aspects is necessary in the design step. The performance achievable by these rotor structures are quantified. An analytical model that describes the mutual interaction between coupled electrical circuits in machines with complex rotor structure is developed. Such a model is useful to analyze the parasitic torques in the torque characteristic of motors with rotor cage such as IM and LS SyM. The literature reveals that this topic has been discussed extensively for IM. As regards LS SyM, there is a lack of theoretical studies regarding harmonic phenomena due to the complex machine structure. This part of the thesis aims to fill this gap. The high and unstable cost of rare-earth PMs, together with the advances in solid-state control technology, leads designers to reconsider IM for variable speed drive (VSD) applications. To the aim of making the IM suitable for the full-speed sensorless control, a particular cage design is considered. An intentionally created saliency is introduced in the rotor so as to allow the rotor position to be estimated by means of a high frequency (HF) injected signal in the stator winding also at zero-speed. Different experimental tests are carried out on IMs with asymmetrical rotor cage to validate the analysis techniques and quantify the achievable performance. As far as the HF signal injection sensorless technique is concerned, the cross-saturation differential inductance of SyMs represents an issue. It causes a rotor position estimation error, reducing the region in which such technique is effective. The proper-ties of the cross-saturation inductance are deeply discussed. It is originally shown that the cross-saturation inductance depends from certain machine parameters. With such an analysis, a designer can consider the effect of the cross-saturation inductance in any model-based control algorithm. A rotor winding is added in Surface-mounted permanent-magnet machine (SPM) to create a HF anisotropy that is useful to detect the rotor position by means of a HF signal injection. Such a configuration is called ”ringed-pole”. In literature, this technique has been used on small-size machines. In certain configuration, the presence of the additional rotor winding causes significant rotor losses. This part of the thesis studies the rotor losses in ringed pole machines by means of FE analysis and analytical models. The aim is to investigate if the ringed-pole technique can be adopted also for large machines from the point of view of additional losses. With few exceptions, the work described in this thesis is always supported by means of experimental measurements. Dedicated experiments has been designed. Their results are compared with those achieved with analytical models or FE analysis.
Questo lavoro di tesi è incentrato sull’analisi, la progettazione e la prototipazione di macchine elettriche trifase ad alto rendimento, con particolare riferimento a motori dotati di avvolgimenti rotorici. Inizialmente si descrivono le motivazioni di questo lavori di tesi e il contesto in cui essa si inserisce, illustrandone i principali obiettivi. Una dettagliata analisi bibliografica è alla base del lavoro svolto. Una selezione di questi lavori si trova nelle referenze. I motori sincroni autoavvianti (LS SyM) sono stati introdotti nella prima metà del novecento e la loro progettazione è soggetto di ricerca sin da allora. Essi non si sono mai affermati a causa della loro difficile progettazione e per la disponibilità del più robusto ed economico motore ad induzione (IM). Dopo aver descritto il principio di funzionamento di IM e LS SyM, se ne illustrano le tecniche di analisi sviluppate fino al giorno d’oggi. Negli ultimi anni vi è un rinnovato interesse verso i LS SyM grazie agli stringenti requisiti di rendimento. Vi è quindi la necessità di tecniche di progettazione veloci ed affidabili per LS SyM. I risultati di simulazioni agli elementi finiti sono stati combinati a modelli analitici per descrivere la complessa dinamica di LS SyM. L’obiettivo è quello di ottenere una risposta sufficientemente precisa in tempi molto più brevi rispetto ad altre tecniche di analisi. In questo modo si rende possibile una rapida e precisa calibrazione dei parametri rotorici necessari per soddisfare determinati requisiti di carico dinamico. Parte di questa tesi è dedicata allo sviluppo di una tecnica di analisi per LS SyM in condizioni di regime. Tale analisi `e condotta nello stesso sistema di riferimento usato nei classici modelli per macchine sincrone non autoavvianti. Si mostra che l’analisi proposta permette anche di ottimizzare alcuni parametri di macchina. Negli ultimi anni vi sono stati numerosi sviluppi nella progettazione di macchine sincrone a riluttanza, con o senza l’assistenza di magneti permanenti. In questa tesi si è voluto investigare sulla possibilità di applicare tali sviluppi ai LS SyM, tenendo in considerazione i vincoli costruttivi legati alla presenza della gabbia rotorica. Lo scopo è quello di ridurre il volume di magneti permanenti utilizzati per contenere i costi di produzione. Si è affrontato il problema dell’industrializzazione dei LS SyM, con particolare riferimento al processo di pressofusione del rotore. Nell’intento di ridurre il ripple di coppia, incrementare la coppia media e ridurre le perdite dei motori elettrici, recenti lavori propongono l’utilizzo di algoritmi di ottimizzazione stocastica nella fase di progettazione. I suddetti obiettivi sono basilari anche per LS SyM, anche se per questo tipo di motori la letteratura è meno fornita. Per questo motivo si è voluto utilizzare un algoritmo di ottimizzazione nella fase di progettazione della lamiera di un LS SyM. L’analisi è applicata ad un LS SyM trifase a 2 poli di piccola taglia, dato che ancora non si trovano nei cataloghi dei principali costruttori. L’ottimizzazione è sviluppata considerando la necessità di ottenere un progetto robusto e comunque adatto alla produzione industriale, dato che tale LS SyM deve essere competitivo con l’ormai consolidato IM. Una promettente struttura rotorica è stata prototipata. Le prestazioni ottenute sono confrontate con quelle del corrispondente IM. Si è proposta un innovativa configurazione di LS SyM per dimostrare la fattibilità del loro utilizzo su scala industriale. Lo scopo è quello di utilizzare la stessa lamiera per motori con un diverso numero di poli, riducendo di conseguenza il costo di produzione. Per fare ciò è necessario un compromesso tra aspetti contrastanti nel progetto. In questa parte di tesi, si è voluto quantificare le prestazioni ottenibili da tali geometrie nelle diverse configurazioni. In questa tesi si è sviluppato un modello analitico per caratterizzare l’interazione di circuiti elettrici accoppiati in strutture complesse quali quelle dei LS SyM. Questa analisi mira ad essere uno strumento per la determinazione analitica delle coppie parassite in motori dotati di gabbia rotorica come LS SyM e IM. La letteratura riporta un gran numero di lavori riguardanti la descrizione di coppie parassite nella caratteristica di coppia di motori IM. In LS SyM, l’analisi delle coppie parassite è molto più complessa a causa della struttura di macchina. In letteratura, gli studi analitici riguardanti gli effetti di armoniche di MMF in motori LS SyM sono pochi ed incompleti. L’elevato ed instabile prezzo dei magneti permanenti, assieme allo straordinario sviluppo dell’elettronica allo stato solido, ha spinto a riconsiderare il motore ad induzione per applicazioni a velocità variabile. In questo scenario, si è considerato un avvolgimento rotorico a gabbia di scoiattolo in cui i conduttori sono asimmetrici. Tale asimmetria permette il riconoscimento sensorless della posizione rotorica tramite iniezione di segnali ad alta frequenza negli avvolgimenti di statore anche a velocità molto basse. Sono stati condotti test sperimentali su prototipi di IM con gabbia asimmetrica allo scopo di verificare le tecniche di analisi e di quantificare le prestazioni ottenibili da tali geometrie. Proseguendo l’analisi delle problematiche riscontrate in controlli di tipo sensorless con iniezione di segnale, si sono approfondite le proprietà della mutua induttanza differenziale causata dal fenomeno della saturazione incrociata tra asse d e q in macchine sincrone. Essa causa un errore nella stima della posizione rotorica, riducendo di fatto l’applicabilità del controllo sensorless con iniezione di segnale. Dopo aver discusso in dettaglio le propriet`a di tale induttanza, si `e dimostrato che essa dipende da alcuni parametri di macchina. Con i risultati ottenuti, può essere intrapresa una serie di accorgimenti nel controllo della macchina volta a mitigare l’effetto negativo dell’induttanza mutua dovuta alla saturazione incrociata. Uno o più avvolgimenti rotorici possono essere introdotti anche in motori sincroni a magneti permanenti superficiali, allo scopo di estendere l’applicabilità del controllo sensorless con iniezione di segnale anche a questo tipo di motori. In questo tipo di macchine, denominate ”ringed-pole”, tali avvolgimenti rotorici possono essere sede di perdite importanti nel funzionamento a regime. In letteratura, questa tecnologia è stata applicata a motori di piccola taglia. In questo contesto, si sono studiate le perdite rotoriche di macchine ”ringed-pole” tramite analisi agli elementi finiti e modelli analitici. Lo scopo è quello di verificare se l’uso di tale tecnologia può essere esteso a macchine di taglia superiore dal punto di vista delle perdite rotoriche. Con poche eccezioni, gli argomenti di questa tesi sono validati tramite misure sperimentali. I risultati delle prove sperimentali sono confrontati con quelli provenienti da modelli analitici o da analisi agli elementi finiti.

The focus of this work is on the steady-state analysis of RE circuits using a coupled device and circuit simulator. Efficient coupling algorithms for both the time-domain shooting method and the frequency-domain harmonic balance method have been developed. A modified Newton shooting method considerably improves the efficiency and reliability of the time-domain analysis. Three different implementation approaches of the harmonic balance method for coupled device and circuit simulation are investigated and implemented. These include the quasi-static, non-quasi-static, and modified-Volterra-series approaches. Comparisons of simulation and performance results identify the strengths and weakness of these approaches in terms of accuracy and efficiency.
Graduation date: 2005

博士
國立中央大學
電機工程學系
101
This dissertation presents a new steady-state visual evoked potential (SSVEP). Different from the general SSVEP using only one frequency flicker for each selection of flash stimulators, this work uses a dual-frequency flicker. This dissertation verifies the feasibility of the proposed method, and the symmetric harmonic phenomena are found in this study. Then this dissertation proposes a novel correlation method for frequency recognition of dual-frequency SSVEP. The results further demonstrate that the proposed correlation method has a higher recognition rate than the widely used fast Fourier transform (FFT)method in the proposed system. Moreover, the dual-frequency embedded with the multi-phase flickering sequences stimulation method is proposed. But the brain is a nonlinear dynamic system, and Electroencephalography (EEG) signal can be regarded as its output. The EEG signals in this dissertation include difference frequencies even phases. However, whether this kind of signals is treated as the meaningful signals is researched.

This work considered the frequency-modulated balanced steady-state free precession (fm-bSSFP) sequence as a tool to provide banding free bSSFP MR images. The sequence was implemented and successfully applied to suppress bandings in various in vitro and in vivo examples. In combination with a radial trajectory it is a promising alternative for standard bSSFP applications. First, two specialized applications were shown to establish the benefits of the acquisition strategy in itself. In real time cardiac imaging, it was shown that the continuous shift in frequency causes a movement of the bandings across the FOV. Thus, no anatomical region is constantly impaired, and a suitable timeframe can be found to examine all important structures. Furthermore, a combination of images with different artifact positions, similar to phase-cycled acquisitions is possible. In this way, fast, banding-free imaging of the moving heart was realized. Second, acquisitions with long TR were shown. While standard bSSFP suffers from increasing incidence of bandings with higher TR values, the frequency-modulated approach provided banding free images, regardless of the TR. A huge disadvantage of fm-bSSFP, in combination with the radial trajectory, is the decrease in signal intensity. In this work a specialized reconstruction method, the multifrequency reconstruction for frequency-modulated bSSFP (Muffm), was established, which successfully compensated that phenomena. The application of Muffm to several anatomical sites, such as inner ear, legs and cardiac acquisitions, proofed the advantageous SNR of the reconstruction. Furthermore, fm-bSSFP was applied to the clinically highly relevant task of water-fat separation. Former approaches of a phase-sensitive separation procedure in combination with standard bSSFP showed promising results but failed in cases of high inhomogeneity or high field strengths where banding artifacts become a major issue. The novel approach of using the fm-bSSFP acquisition strategy with the separation approach provided robust, reliable images of high quality. Again, losses in signal intensity could be regained by Muffm, as both approaches are completely compatible. Opposed to conventional banding suppression techniques, like frequency-scouts or phase-cycling, all reconstruction methods established in this work rely on a single radial acquisition, with scan times similar to standard bSSFP scans. No prolonged measurement times occur and patient time in the scanner is kept as short as possible, improving patient comfort, susceptibility to motion or physiological noise and cost of one scan. All in all, the frequency-modulated acquisition in combination with specializes reconstruction methods, leads to a completely new quality of images with short acquisition times
In dieser Arbeit wird eine Modifikation der balanced steady-state free precession (bSSFP) Sequenz betrachtet. Die frequenzmodulierte bSSFP-Sequenz (fm-bSSFP) kann die sonst typischen Band-Artefakte in bSSFP-MR-Bildern verhindern. Die Sequenz wurde im Rahmen der Arbeit am MR-Scanner implementiert und erfolgreich in verschiedenen in-vitro- und in-vivo-Beispielen angewendet. In Kombination mit einer radialen Trajektorie erwies es sich als eine vielversprechende Alternative für alle Standard-bSSFP Anwendungen. Zuerst wurden zwei spezialisierte Anwendungen gezeigt, um die Vorteile der Akquisitionsstrategie an sich darzustellen. Am Beispiel der Echtzeit-Herzbildgebung konnte mit Hilfe der kontinuierlichen Frequenzverschiebung eine Bewegung der Bänder über das FOV erzeugt werden. Somit wird keine anatomische Region ständig von Artefakten überlagert und für jeden Bereich kann ein geeigneter Zeitrahmen gefunden werden, um die wichtigen Strukturen darzustellen und zu untersuchen. Darüber hinaus ist eine Kombination von Bildern mit verschiedenen Artefaktpositionen möglich, ähnlich zu mehreren Aufnahmen mit verschiedenen Phasenzyklen. Auf diese Weise wurde eine schnelle Bildgebung des sich bewegenden Herzens ohne Bandartefakte realisiert. Zusätzlich wurden Aufnahmen mit langen Repetitionszeiten (TR) untersucht. Während in der Standard-bSSFP die Häufigkeit von Bandartefakten mit steigendem TR-Wert zunimmt, lieferte der frequenzmodulierte Ansatz Banding-freie Bilder unabhängig vom TR. Ein großer Nachteil von fm-bSSFP in Kombination mit der radialen Trajektorie ist der Verlust von Signalintensität bei der Rekonstruktion. In dieser Arbeit wurde eine spezielle Rekonstruktionsmethode namens Muffm (mulitfrequency reconstruction for frequency-modulated bSSFP) etabliert, die diesen Verlust erfolgreich kompensieren kann. Die Anwendung von Muffm an verschiedenen anatomischen Strukturen, wie Innenohr, Bein und Herzaufnahmen, bestätigte das vorteilhafte Signal-zu-Rausch-Verhältnis, dass durch die spezielle Rekonstruktion gewonnen werden kann. Darüber hinaus wurde die fm-bSSFP auf die klinisch interessante Wasser-Fett-Trennung angewandt. Frühere Ansätze eines phasenempfindlichen Trennverfahrens in Kombination mit Standard-bSSFP zeigten vielversprechende Ergebnisse, scheiterten jedoch in Fällen hoher Inhomogenität oder hoher Feldstärken an den auftretenden Bandartefakten. Der neue Ansatz, diesen Separationsalgorithmus mit der fm-bSSFP-Akquisitionsstrategie zu verbinden, lieferte robuste, zuverlässige Bilder von hoher Qualität. Auch hier konnten entstehende Verluste in der Signalintensität durch Muffm zurückgewonnen werden, da beide Ansätze vollständig kompatibel sind. Im Gegensatz zu herkömmlichen Bandunterdrückungstechniken, wie Frequenz-Scouts oder die Aufnahme mehrerer Bilder mit verschiedenen Phasenzyklen, beruhen alle in dieser Arbeit etablierten Rekonstruktionsverfahren auf einer einzigen radialen Aufnahme. Die Messzeiten sind daher identisch zur Aufnahme einer Standard-bSSFP Messung. Das Verfahren ermöglicht eine deutliche Verkürzung der Aufenthaltsdauer im Scanner bei einer gleichzeitigen Garantie ein artefaktfreies Bild zu erhalten. Damit ist es insbesondere für Patienten von Vorteil, die unter Platzangst oder sonstigen Beschwerden leiden, die ein langes Stillliegen erschweren. Außerdem werden Bewegungsartefakte, physiologisches Rauschen und nicht zuletzt die Kosten eines Scans minimiert. Insgesamt bietet die frequenzmodulierte bSSFP Aufnahme in Kombination mit spezialisierten Rekonstruktionsverfahren neue Möglichkeiten zur schnellen Aufnahme von Bildern ohne Bandartefakte

no
Cone isolating stimuli were used to assess the temporal frequency response characteristics of L- and M-cone electroretinograms (ERGs) in nine trichromatic and four dichromatic human observers. The stimuli comprised sinusoidal temporal modulations varying from 5 to 100 Hz. ERGs were recorded using corneal fiber electrodes and subjected to fast Fourier transform analysis. At low temporal frequencies (<10  Hz<10  Hz) the L- and M-cone ERGs had similar amplitude and exhibited minimal differences in apparent latency. At higher flicker rates (>20  Hz>20  Hz) L-cone ERGs had greater amplitudes and shorter apparent latencies than the M-cone responses. These differences between the L- and M-cone ERGs are consistent with their mediation by chromatic and luminance postreceptoral processing pathways at low and high temporal frequencies, respectively.

This study evaluated the effect of 3 different modulation rates and 3 different rate separations on the interactions (response amplitudes) of multiple ASSRs. Responses from 12 normal-hearing subjects were examined using three amplitude-modulation rates (14,40 and 80 Hz) and four conditions: one tone (1000 Hz), two tones (1000 and 2000 Hz, presented monotically or dichotically) and four tones (500, 1000,2000 and 4000 Hz, presented monotically). Within the multiple-tone conditions, rate separation between the amplitudemodulated tones was varied from 2 to 6 Hz. A 1000-Hz tone served as the baseline condition and interactions between tones were measured as a function of the change in response amplitude from this baseline. Results indicate separation between modulation rates had no effect on the interactions between responses. Both modulation rate and condition had significant effects on ASSR interactions. In general, interactions became greater as the number of stimuli increased from 1 to 4 tones. However, each modulation rate had a different pattern of interactions. The response amplitudes for all modulation rates were significantly decreased in the four-tone condition. The two-tone dichotic condition amplitudes were decreased from the baseline for the 40-Hz ASSRs, but not for the 14- and 80-Hz ASSR amplitudes. Furthermore, the 40-Hz and 80- Hz two-tone monotic condition response amplitudes were decreased from the baseline, but not the 14-Hz ASSR amplitudes. Results from relative efficiency calculations indicate that at high intensities (80 dB SPL), ASSRs to multiple tones are not more efficient than ASSRs to single tones for any modulation rate range. The different patterns suggest that the 14-, 40- and 80-Hz ASSRs are generated in different areas along the auditory pathways. These results may be helpful in determining the usefulness of multiple ASSRs for diagnostic testing at high intensity levels and for testing auditory functioning at different levels in the auditory pathways. [Research supported by BCMSF, NSERC and CIHR.
Medicine, Faculty of
Audiology and Speech Sciences, School of
Graduate

碩士
國立交通大學
生醫工程研究所
100
To understanding the brain functions via the brain-computer interface (BCI), here, we studied the steady-state visual evoked potentials (SSVEP) from retinal fovea and extrafoveal in response to a 2牵 circular and a 16牵–18牵 annular white light stimuli flickering between 5 and 65 Hz by 5 Hz increments. Eight subjects (age 20~55 years old) participated in this experiment. Their EEG signals were recorded using a commercial 64-channel NeuroScan system. Their flickering perception and comfort levels were also studied. Spectral and canonical correlation analyses of SSVEP signals collected from nine EEG channels in the occipital area showed distinctively higher signal-to-noise ratios (SNR) in the foveal responses between 25 and 45 Hz. The findings from the subjects also indicate that the less flickering and felt are more comfortable with stimulation flickering between 30 and 45 Hz. These empirical evidences suggest that lights flashing above human vision flicker fusion thresholds can be potentially used as an effective visual stimuli tool in SSVEP BCI applications.

碩士
國立成功大學
光電科學與工程學系
100
In this thesis, we demonstrate the use of optical method, steady state frequency domain photon migration system (SSFDPM), to determine physiological parameters of biological tissues. It uses near-infrared light (from 600 to 1100 nm) coupled with mathematical photon transport models to accurately determine optical absorption (µa) and reduced scattering (µs′) properties of tissues. Absorption coefficient (µa) and reduced scattering coefficient (µs′) can be used to determine the chromophore concentrations, such as oxygenated hemoglobin, deoxygenated hemoglobin, water, and lipid, of biological tissues. Here, we employed the diffusing probe with the SSFDPM technique to quantify the optical properties of in-vivo skin. First, we characterize the stability of the amplitude and phase of the frequency domain photon migration system (FDPM) so that we can understand the limitations of our system. Second, we prepare four samples of different absorption to study the system linearity. Third, we use FDPM system to measure six liquid phantoms of various absorption and scattering properties. Finally, we combine the steady state (SS) and FDPM which is called SSFDPM to measure the liquid phantom, and quantify the chromophore concentrations of liquid phantoms. In addition, we carry out SSFDPM measurements on the in-vivo dorsal forearm and show the quantitative physiological concentration and compare with SS measurements. Our study reveals that the SSFDPM system provides a fast and noninvasive way for tissue composition quantification.

The Auditory Steady State Response (ASSR) procedure has been established as a frequency specific, objective audiologic measure, which can provide reliable thresholds to within 10 dB of the behavioral thresholds. In order for ASSR to find its place in the existing framework of audiometric procedures, the full potential of the procedure needs to be explored. The aim of this study was to determine the accuracy of monotic ASSR in estimating hearing thresholds in a group of 15 normal hearing subjects and 15 hearing-impaired subjects. A comparative research design was implemented. Indicating that results obtained in the study was compared to relevant literature where dichotic multiple ASSR was implemented. This was done in order to ascertain ASSR’s capabilities with regard to stimulus presentation methods. Monotic single ASSR predicted behavioural thresholds in the normal hearing subjects within an average of 24 dB across the frequency range (0.5, 1, 2&4 kHz). In the hearing-impaired group, ASSR thresholds more closely resembled behavioural thresholds, with an average difference of 18 dB, which is consistent with recent literature. The literature suggests that better prediction of behavioural thresholds will occur with greater degrees of hearing loss, due to recruitment. The focus in this group also centered on the accurate prediction of the configuration of the hearing loss. It was found that ASSR could reasonably accurately predict the configuration of the hearing loss. In the last instance, monotic single and dichotic multiple ASSR were compared with regard to threshold estimation and prediction of configuration of the hearing loss in the hearing-impaired group. Little difference was reported between the two techniques with regard to the estimation of thresholds in both the normal hearing and hearing impaired groups. In conclusion it was established that monotic ASSR could predict behavioural thresholds of varying degrees and configurations of hearing loss in normal and hearing-impaired subjects with a reasonable amount of accuracy. At this stage, however, more research is required to establish the clinical validity of the procedure, before it is routinely included within an objective test battery.
Dissertation (M (Communication Pathology))--University of Pretoria, 2005.
Speech-Language Pathology and Audiology
Unrestricted

碩士
逢甲大學
電機工程所
92
To design a reliable and economical high voltage and high frequency transformer, it is necessary to be able to predict accurately the temperature distribution within the transformer. For thermal analysis, this thesis presents a model for the transformer. Then, the three-dimensional finite element method is conducted to analyze. Due to the complicated physical geometry of the transformer, such as the anisotropic nature of the iron, low and high voltage windings, insulation layers and insulation oil, a two-dimensional thermal model can not describe the problem accurately. Hence, a three-dimensional thermal model is employed for this analysis. To reduce the simulation time, the equivalent thermal conductivities for low and high voltage windings are derived based on the choice of proper size of three-dimensional tetrahedral elements. Reasonable results are obtained.

碩士
高雄醫學大學
職業安全衛生研究所
96
Objective: This study evaluated the usefulness of dichotic multiple-frequency auditory steady-state response (Mf-ASSR) to predict hearing threshold and audiogram of noise-induced hearing impaired in noise exposure workers. To evaluate the accuracy, using statistical methods, of the prediction of Mf-ASSRs in a large sample of sensorineural hearing impairment subjects with and without noise exposure. Design: The Mf-ASSR was recorded in a sample of 34 noise-induced hearing impairment workers (NIHL) and 36 non-noise-exposure hearing impaired subjects. Simultaneous carrier frequencies (0.5, 1, 2, and 4kHz) were presented binaurally. The correlation of Mf ASSR and behavioral thresholds were evaluated across all subjects. The accuracy of ASSR thresholds was compared across groups. A predicting equation with multivariate was calculated. Results: The results showed that, on average, ASSR threshold curves corresponded well with behavioral audiometric contour averaged across subjects. Multiple-ASSR threshold were 20±8, 16±9, 12±9 and 11±12dB above behavioral thresholds for 0.5, 1, 2, and 4 kHz, respectively. Behavioral and multiple-ASSR thresholds were significantly correlated (r=0.77-0.89). We confirmed the ASSR to be used in predicting hearing threshold in the noise-induced hearing-impaired subjects. ASSR and behavioral thresholds were strongly correlated across all subjects, with r-value between 0.85~0.95. And the r-square of the predicting regression equation was 0.9. In three-way repeated measures analysis of variance, the difference thresholds between ASSR and behavioral thresholds were significant higher in the NIHL subjects than in non-noise-exposure hearing-impaired subjects and for the 500Hz frequency compared with the higher frequencies. Conclusions: Noise exposure or not and carrier frequency have a significant effect on steady state response. Mf -ASSR was proved to be a valid technique for estimating hearing thresholds, and a mixed model of regression equation can accurately predict the thresholds with all the effect factors.

碩士
國立中央大學
電機工程研究所
95
The present study proposes a new visual evoked potential (VEP)-based brain computer interface (BCI). Users gaze at different spatially separated flash channels (FCs) in order to induce visual evoked signals that have temporal sequences corresponding to the gazed FCs, so that the gazed FC can be recognized and the command mapping to the gazed FC can be sent out to achieve control purposes. To achieve distinct flickering sequences among different FCs, we utilized different frequencies and phases to encode the flashing sequences of different FCs. The proposed system provides the high flexibility in expansion of FC number and high information transfer rate (ITR) which are superior to the traditional SSVEP-based and FVEP-based BCIs. In this thesis, we have built an eight-FC system. The command transfer rate and detected accuracy are 0.52 sec/command and 100%, respectively.

Audiologists are reliant on objective audiometric procedures to predict auditory sensitivity in difficult-to-test populations. A technique to estimate frequency-specific hearing thresholds in a time-efficient way for difficult-to-test populations, who are unable to provide behavioural responses, has long been the hope of audiologists. The auditory brainstem response (ABR) has dominated the field of objective electrophysiological audiometry for the past three decades. Although it provides a useful method of estimating auditory sensitivity, it presents with its own set of limitations. Recently the auditory steady state response (ASSR) has demonstrated promise of addressing the limitations of the ABR as it is an evoked response uniquely suited to frequency-specific measurement. An optimised version of the ASSR, the dichotic multiple frequency (MF) ASSR, has been proposed as a time-efficient way of evaluating different frequencies simultaneously in both ears. The aim of this study was to evaluate the clinical usefulness of the dichotic MF ASSR technique for estimating pure tone behavioural thresholds at 0.5, 1, 2, and 4 kHz, compared to a 0.5 kHz tone burst and broadband click ABR protocol in a sample of normal hearing adults (56 ears). A comparative experimental research design was selected in order to compare thresholds obtained with the different procedures. The results indicated that both the dichotic MF ASSR and a 0.5 kHz tone burst and broadband click ABR protocol provided a reasonable estimation of PT behavioural thresholds in a time-efficient manner for a group of normal hearing subjects. The click ABR did, however, present with 1, 2, and 4 kHz PT threshold estimations that were almost 50 % closer than that of the dichotic MF ASSR according to the mean and normal deviation. This increased accuracy and reliability of the click ABR is however compromised by its lack of frequency-specificity. In the low frequency region of 0.5 kHz, the tone burst ABR and dichotic MF ASSR evidenced estimations of the pure tone threshold that were, on average, very similar. The tone burst ABR, however, presented with a mean threshold slightly (3 dB) closer to the pure tone threshold than the dichotic MF ASSR. The 0.5 kHz dichotic MF ASSR presented with a smaller range of normal deviation in the estimation of pure tone thresholds which suggested a more reliable measure than the 0.5 kHz tone burst ABR. The dichotic MF ASSR evaluation provided eight thresholds (4/ear) in 23 minutes on average compared to 25 minutes on average required by the ABR protocol to evaluate 4 thresholds (2/ear). This research concluded that the dichotic MF ASSR is useful for estimating frequency-specific pure tone thresholds reasonably well in a time-efficient manner but that this technique should be used in a test-battery alongside the ABR. Both the dichotic MF ASSR and the ABR comprise unique qualities that can be combined in a cross-check principle approach in order to provide complementary information that will verify results obtained with each procedure.
Dissertation (MA (Communication Pathology))--University of Pretoria, 2006.
Speech-Language Pathology and Audiology
Unrestricted

There has always been a need for objective tests that assess auditory function in infants, young children, and/or any patient whose development level precludes the use of behavioral audiometric techniques. Although the Auditory Brainstem Response (ABR) is seen as the ‘gold standard’ in the field of objective audiometry, it presents with its own set of limitations. The Auditory Steady State Response (ASSR) has gained considerable attention and is seen as a promising addition to the AEP ‘family’ to address some of the limitations of the ABR. The ASSR promises to estimate all categories of hearing loss (mild to profound) in a frequency specific manner. It also indicates to the possibility to validate hearing aid fittings by determining functional gain of hearing aids by determining unaided and aided ASSR thresholds. An exploratory research design was selected in order to compare unaided thresholds, obtained through the use of three different procedures – ABR, ASSR and behavioral thresholds. Aided thresholds were also obtained and compared with two procedures – the aided ASSR (measured and predicted) and aided behavioral threshold. The results indicated that both the ABR (tone burst and click) and ASSR provided a reasonable estimation of the subsequently obtained behavioral audiograms. The ASSR, however, approximated the behavioral thresholds closer than the ABR and were furthermore able to quantify hearing thresholds accurately for subjects with severe and profound hearing losses. The result indicated further that the ASSR can be instrumental in the validation process of hearing aid fittings in infants. These results demonstrated however, that the ASSR measured thresholds underestimate the aided behavioral thresholds and the aided ASSR predicted thresholds overestimate the aided behavioral thresholds. The research concluded that the ASSR is useful in estimating frequency-specific behavioral thresholds accurately in infants and validating hearing aid fittings. Until evidence is sufficient to recommend the ASSR as primary electrophysiological measure of hearing in infants, the ASSR should be used in conjunction with the ABR – following a test battery approach in the diagnostic process of hearing loss in infants. The ASSR further shows great promise in validating hearing aid fittings, but this specific application of the ASSR needs further research evidence on large groups to validate the procedure.
Dissertation (Master of Communication Pathology)--University of Pretoria, 2007.
Speech-Language Pathology and Audiology
unrestricted