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The data processing to detect correlated movement of Cerebral Palsy patient in early phasePyon, Okmin 03 February 2016 (has links)
The early diagnosis of CP (Cerebral Palsy) in infants is important for developing meaningful interventions. One of the major symptoms of the CP is lack of the coordinated movements of a baby. The bilateral coordinated movement (BCM) is that a baby shows in the early development stage. Each limb movement shows various ranges of speed and angle with fluency in a normal infant. When a baby has CP the movements are cramped and more synchronized.
A quantitative method is needed to diagnose the BCM. Data is collected from 3-axis accelerometers, which are connected, to each limb of the baby. Signal processing the collected data using short time Fourier transforms, along with the formation of time-dependent transfer functions and the coherence property is the key to the diagnostic approach. Combinations of each limb's movement and their relationship can represent the correlated movement. Data collected from a normal baby is used to develop the technique for identifying the fidgety movement. Time histories and the resulting diagnostic tool are presented to show the regions of the described movement. The evaluation of the transduction approach and the analysis is discussed in detail.
The application of the quantitative tool for the early diagnosis of CP offers clinicians the opportunity to provide interventions that may reduce the debilitating impact this condition has on children. Tools such as this can also be used to assess motor development in infants and lead to the identification and early intervention for other conditions. / Master of Science
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Analyse temps-fréquence en mécanique cellulaire et adaptabilité du fuseau mitotique / Time-frequency analysis in cell mechanics and adaptability of mitotic spindleMercat, Benjamin 04 October 2016 (has links)
Le fuseau mitotique assure la ségrégation des chromatides sœurs et le maintien de la poïdie des cellules filles. Le fuseau est composé de microtubules dynamiques (qui polymérisent et dépolymérisent continuellement), de nombreux moteurs moléculaires, d'agents de réticulations et de régulateurs. Bien que la structure du fuseau au niveau moléculaire soit connue, son fonctionnement reste délicat à comprendre, et nécessite la prise en compte de la dynamique de ses composants et leurs interactions. Les approches utilisées pour répondre à ces problématiques sont jusqu'à maintenant plutôt des approches in silico et in vitro. Il manque aujourd'hui une caractérisation de la mécanique du fuseau dans son contexte physiologique. Nous proposons une méthode non invasive basée sur de l'analyse d'image, combiné à une modélisation heuristique pour mesurer les paramètres mécaniques durant toute la division. Nous suivons les pôles du fuseau marqués par protéine fluorescente avec un taux acquisition rapide et une bonne résolution spatiale ce qui nous permet d'accéder aux fluctuations de longueur du fuseau in vivo. Avec la transformée de Fourier aux temps courts, nous calculons leurs densités spectrales de puissances — leurs signatures mécaniques. Ces spectres sont alors ajustés avec un modèle Kelvin — Voigt avec inertie (un ressort, un amortisseur et un terme inertiel en parallèle). Nous avons validé la méthode par des expériences numériques où nous retrouvons les évolutions des paramètres sur des données simulées et la calibration a été réalisée par l'utilisation de la rupture du fuseau induite par micro chirurgie laser ou par la génétique. Nous avons caractérisé le fuseau de l'embryon unicellulaire du nématode C. elegans. La méthaphase apparaît dominée par l'amortisseur, ce qui est cohérent avec la lente élongation du fuseau que nous observons. Mais contraste l'idée répandue de l'existence d'un mécanisme de maintien de la longueur du fuseau durant la métaphase. Au passage en anaphase, les trois paramètres mécaniques chutent, avant de réaugmenter environ 50 secondes après la transition pour réatindre un régime dominé de nouveau par l'amortisseur, ce qui suggère que les microtubules interpolaires jouent un rôle mineur durant l'élongation du fuseau en début d'anaphase. Dans la perspective de comprendre le lien entre la mécanique du fuseau et les interactions des acteurs moléculaires, nous avons partiellement supprimé un gène par sous-structure du fuseau. Nous avons alors retrouvé des comportements connus avec une perspective augmentée offerte par notre méthode. Cette méthode, ne va pas seulement permettre la compréhension fondamentale de la mécanique du fuseau, en remplaçant la modélisation du fuseau basé uniquement sur la longueur, mais aussi d'aller vers la prise en compte de la robustesse de fonctionnement du fuseau mitotique face aux défauts tel que la polyou l'aneuploïdie. / The mitotic spindle ensures the correct segregation of the sister chromatids to maintain ploidy in daughter cells. The spindle comprises dynamical microtubules (alternating polymerizing and depolymerizing), a variety of molecular motors, crosslinker and the regulators. Although the molecular grounds of spindle structure is well known, the link to its functions remain elusive, calling for including the dynamics of its components and their interactions. These questions were mostly investigated by in silico or in vitro approaches. But a detailed characterizing of spindle mechanics, in physiological conditions, is missing. We propose an image processing based, non invasive, method combined to an heuristic model to measure mechanical parameters of the mitotic spindle along time. We tracked fluorescently labeled spindle pole at high temporal and spatial resolution and measured the variations of spindle length, in vivo. We computed their power density spectrum using short time Fourier transform (sliding window) — a blueprint of spindle mechanics. Such a spectrum is then fitted with a Kelvin —Voigt model with inertia (a spring, a damper, an inertial element in parallel). We validated this method by recovering the mechanical parameters over time from simulated data and calibrated it uses laser and genetically induced spinlde cut. We characterized the mitotic spindle of the one-cell embryo of nematode C. elegans. Metaphase appeared dominated by damping element, consistent with the slow spindle elongation observed. But in contrast with the common thought that a mechanism maintains the spindle length during metaphase. At anaphase onset, all three parameters collapsed, before increasing about 50s later to reach a regime where damping dominated again, suggesting the overlapping spinlde microtubules may play a minor role in early anaphase spinlde elongation. In perspective of understanding how spindle mechanics emerge of molecular players interactions, we depleted one gene per splindle sub-structure — overlapped microtubules, kinetochore microtubules, central spindle and astral microtubules. We succefully recovered some known behavior but with the augmented insight offered by our method. This method paves the way not only towards understanding the fundamentals of spindle mechanics, superseding the degenerated modeling based on the sole spindle length but also towards acounting for spindle functional robustness towards defect as polyor aneuploidy.
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Realization Of A Cue Based Motor Imagery Brain Computer Interface With Its Potential Application To A WheelchairAkinci, Berna 01 October 2010 (has links) (PDF)
This thesis study focuses on the realization of an online cue based Motor Imagery (MI) Brain Computer Interface (BCI). For this purpose, some signal processing and classification methods are investigated. Specifically, several time-spatial-frequency methods, namely the Short Time Fourier Transform (STFT), Common Spatial Frequency Patterns (CSFP) and the Morlet Transform (MT) are implemented on a 2-class MI BCI system. Distinction Sensitive Learning Vector Quantization (DSLVQ) method is used as a feature selection method. The performance of these methodologies is evaluated with the linear and nonlinear Support Vector Machines (SVM), Multilayer Perceptron (MLP) and Naive Bayesian (NB) classifiers. The methodologies are tested on BCI Competition IV dataset IIb and an average kappa value of 0.45 is obtained on the dataset. According to the classification results, the algorithms presented here obtain the 4th level in the competition as compared to the other algorithms in the competition.
Offline experiments are performed in METU Brain Research Laboratories and Hacettepe Biophysics Department on two subjects with the original cue-based MI BCI paradigm. Average prediction accuracy of the methods on a 2-class BCI is evaluated to be 76.26% in these datasets. Furthermore, two online BCI applications are developed: the ping-pong game and the electrical wheelchair control. For these applications, average classification accuracy is found to be 70%.
During the offline experiments, the performance of the developed system is observed to be highly dependent on the subject training and experience. According to the results, the EEG channels P3 and P4, which are considered to be irrelevant with the motor imagination, provided the best classification performance on the offline experiments. Regarding the observations on the experiments, this process is related to the stimulation mechanism in the cue based applications and consequent visual evoking effects on the subjects.
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Pilot-induced oscillation detection and mitigationLiu, Qingling 12 1900 (has links)
Commercial Aircraft
Corporation of China, Ltd (COMAC)and Chinese Scholarship Council. / The aim of this thesis is to develop a real time PIO detection and mitigation system that
consists of a detector based on short time Fourier transform(STFT) and autoregressive
model(ARX) with exogenous inputs, together with an adaptive controller based mitigation
system. The system not only detects the traditional PIO characteristics but also focuses on
the trend of pilot behaviour by calculating the rate of change in the open loop crossover
frequency. In the detection system, a sliding windowed STFT method was applied to
identify the frequency and phase characteristics of the system via processing the signal of
pilot input and aircraft state. An ARX model was also applied to get the rate of change
of the crossover frequency. After detection, a PIO cue was shown on the primary flight
display. A scheduled gain controller was coupled to provide PIO mitigation by varying
stick input gain.
Compensatory and tracking tests for the evaluation of this system were performed using
a quasi-linear Boeing-747 aircraft model including nonlinear command gearing and actuator
rate-limiting. Bandwidth and Gibson criteria were used to design PIO prone control
laws for system evaluation experiments. Results from PIO tests conducted on desktop
PCs were presented. These were analyzed and compared with those obtained from implementing
the Real-time Oscillation Verifier module available in literature.
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Feasibility of Using Electrical Network Frequency Fluctuations to Perform Forensic Digital Audio AuthenticationEl Gemayel, Tarek 06 August 2013 (has links)
Extracting the Electric Network Frequency (ENF) fluctuations from an audio recording and comparing it to a reference database is a new technology intended to perform forensic digital audio authentication. The objective of this thesis is to implement and design a range of programs and algorithms for capturing and extracting ENF signals. The developed C-program combined with a probe can be used to build the reference database. Our implementation of the Short-Time Fourier Transform method is intended for the ENF extraction of longer signals while our novel proposed use of the Autoregressive parametric method and our implementation of the zero-crossing approach tackle the case of shorter recordings. A Graphical User Interface (GUI) was developed to facilitate the process of extracting the ENF fluctuations. The whole process is tested and evaluated for various scenarios ranging from long to short recordings.
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Feasibility of Using Electrical Network Frequency Fluctuations to Perform Forensic Digital Audio AuthenticationEl Gemayel, Tarek January 2013 (has links)
Extracting the Electric Network Frequency (ENF) fluctuations from an audio recording and comparing it to a reference database is a new technology intended to perform forensic digital audio authentication. The objective of this thesis is to implement and design a range of programs and algorithms for capturing and extracting ENF signals. The developed C-program combined with a probe can be used to build the reference database. Our implementation of the Short-Time Fourier Transform method is intended for the ENF extraction of longer signals while our novel proposed use of the Autoregressive parametric method and our implementation of the zero-crossing approach tackle the case of shorter recordings. A Graphical User Interface (GUI) was developed to facilitate the process of extracting the ENF fluctuations. The whole process is tested and evaluated for various scenarios ranging from long to short recordings.
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Diagnóstico de fallos electromecánicos en motores eléctricos mediante el análisis avanzado del flujo magnético y su implementación en hardwareZamudio Ramírez, Israel 10 October 2023 (has links)
[ES] Los motores eléctricos son máquinas eléctricas rotatorias que permiten realizar la conversión de energía eléctrica en energía mecánica, misma que resulta de gran utilidad en diversos procesos industriales, principalmente para accionar mecanismos y cadenas cinemáticas complejas que ejecutan alguna tarea en específico. Dentro de los distintos tipos de motores eléctricos, las máquinas de inducción se han utilizado ampliamente en una gran variedad de procesos industriales. Esto se debe principalmente a sus excelentes características y prestaciones, como lo son: robustez, fácil control, simplicidad, confiabilidad, y fácil mantenimiento. Sin embargo, a pesar de su elevada robustez, este tipo de máquinas se encuentran sujetas a esfuerzos mecánicos, térmicos, eléctricos y ambientales bajo diversas condiciones de operación durante su vida útil, lo que de forma inevitable conduce a fallos. Los principales fallos que suelen presentarse en los motores eléctricos de inducción son aquellos relacionados a sus componentes internos como lo son barras de rotor rotas, desgaste en las pistas exterior e interior en los rodamientos, desgaste en la jaula del rodamiento, fallas en el estator (por ejemplo, cortocircuito entre espiras adyacentes), entre otros. Cuando un motor eléctrico se encuentra operando bajo alguna condición de falla su rendimiento puede verse afectado, lo que se traduce en consumos de energía más elevados, causando a su vez costos extras al momento de facturar. En este trabajo de investigación se presenta el desarrollo de una metodología innovadora, capaz de generar un diagnóstico adecuado y de forma automática de la ocurrencia de las fallas más comunes que pueden desarrollarse en los motores eléctricos de inducción bajo diversas condiciones de operación mediante el análisis del flujo magnético de dispersión (que puede ser capturado en la periferia del marco del motor) empleando herramientas de descomposición en tiempo-frecuencia, herramientas de clasificación de datos y parámetros de caracterización de señales. Así entonces, se prueba la validez de técnicas basadas en el análisis del flujo magnético de dispersión para el diagnóstico de distintas fallas electromecánicas en motores de inducción. Los resultados demuestran el excelente desempeño de la metodología de diagnóstico automático propuesta, al ser evaluada en una gran variedad de motores con diversas características constructivas. / [CA] Els motors elèctrics són màquines elèctriques rotatòries que permeten realitzar la conversió d'energia elèctrica en energia mecànica, la qual cosa resulta de gran utilitat en diversos processos industrials, principalment per a accionar mecanismes i cadenes cinemàtiques complexes que executen alguna tasca en específic. Dins dels diferents tipus de motors elèctrics, les màquines d'inducció s'han utilitzat àmpliament en una gran varietat de processos industrials. Això es deu principalment a les seues excel·lents característiques i prestacions, com ara robustesa, fàcil control, simplicitat, fiabilitat i fàcil manteniment. No obstant això, malgrat la seua elevada robustesa, aquest tipus de màquines estan sotmeses a esforços mecànics, tèrmics, elèctrics i ambientals en diverses condicions d'operació durant la seua vida útil, la qual cosa inevitablement condueix a fallades. Les principals fallades que solen presentar-se en els motors elèctrics d'inducció són aquelles relacionades amb els seus components interns, com ara barres de rotor trencades, desgast en les pistes exterior i interior dels rodaments, desgast en la gàbia del rodaments, fallades en l'estator (per exemple, curtcircuit entre espires adjacents), entre altres. Quan un motor elèctric està funcionant sota alguna condició de fallada, el seu rendiment pot veure's afectat, la qual cosa es tradueix en consums d'energia més elevats, causant al seu torn costos addicionals en el moment de facturar. En aquest treball d'investigació es presenta el desenvolupament d'una metodologia innovadora, capaç de generar un diagnòstic adequat i de forma automàtica de l'ocurrència de les fallades més comunes que poden desenvolupar-se en els motors elèctrics d'inducció sota diverses condicions d'operació mitjançant l'anàlisi del flux magnètic de dispersió (que pot ser capturat en la perifèria del marc del motor) emprant eines de descomposició en temps-freqüència, eines de classificació de dades i paràmetres de caracterització de senyals. Així doncs, es prova la validesa de tècniques basades en l'anàlisi del flux magnètic de dispersió per al diagnòstic de diferents fallades electromecàniques en motors d'inducció. Els resultats demostren l'excellent rendiment de la metodologia de diagnòstic automàtic proposada, en ser avaluada en una gran varietat de motors amb diverses característiques constructives. / [EN] Electric motors are rotating electrical machines that allow the conversion of electrical energy into mechanical energy, which is very useful in various industrial processes, mainly to drive mechanisms and complex kinematic chains that perform a specific task. Within the different types of electric motors, induction machines have been widely used in a wide variety of industrial processes. This is mainly due to its excellent features and benefits, such as robustness, easy control, simplicity, reliability, and easy maintenance. However, despite its high robustness, this type of machine is subject to mechanical, thermal, electrical, and environmental stress under various operating conditions during its useful life, which inevitably leads to failures. The main failures that usually occur in electric induction motors are those related to their internal components, such as broken rotor bars, wear on the outer and inner races of the bearings, wear on the bearing cage, stator failures ( for example, short circuit between adjacent turns), among others. When an electric motor is operating under some fault condition, its performance may be affected, which translates into higher energy consumption, causing extra costs at the time of billing. This research thesis presents the development of an innovative methodology capable of automatically generating an adequate diagnosis of the occurrence of the most common failures that can develop in electric induction motors under various operating conditions through the analysis of the stray magnetic flux (which can be captured at the periphery of the motor frame). This is performed by using time-frequency decomposition tools, data classification tools, and signal characterization parameters. Thus, the validity of techniques based on the analysis of the stray magnetic flux for the diagnosis of different electromechanical failures in induction motors is tested. The results demonstrate the excellent performance of the proposed automatic diagnosis methodology when evaluated in a wide variety of engines with different construction characteristics. / Zamudio Ramírez, I. (2023). Diagnóstico de fallos electromecánicos en motores eléctricos mediante el análisis avanzado del flujo magnético y su implementación en hardware [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/197989
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Microlocal Analysis of Tempered DistributionsSchulz, René M. 12 September 2014 (has links)
Diese Dissertation ist dem Studium temperierter Distributionen mittels mikrolokaler Methoden gewidmet. Die fundamentale Größe der mikrolokalen Analysis, die Wellenfrontmenge, wird durch zwei analoge Konzepte ersetzt, die den pseudo-differentiellen SG- und Shubin-Kalkülen zugeordnet sind. Die Eigenschaften dieser globalen Wellenfrontmengen werden studiert und ferner werden unterschiedliche Möglichkeiten, diese globalen Singularitäten zu charakterisieren, untersucht, insbesondere mittels der FBI-Transformation.
Zahlreiche Konstruktionen, die den klassischen Wellenfrontmengenbegriff beinhalten, werden in den globalen Kontext übersetzt, insbesondere Rechenoperationen mit temperierten Distributionen wie etwa (getwistete) Produkte, Pull-backs und Paarungen, für die mikrolokale Existenzkriterien angegeben werden.
Als eine Anwendung wird eine Klasse von temperierten Oszillatorintegralen eingeführt, welche durch inhomogene Phasenfunktionen und Amplituden aus SG-Symbolklassen parametrisiert werden. Die SG-Wellenfrontmengen dieser Distributionen werden untersucht und es stellt sich heraus, dass diese durch eine Verallgemeinerung der Menge stationärer Punkte der Phasenfunktionen beschränkt werden.
In diesem Kontext wird eine Verallgemeinerung des klassischen Begriffs einer konischen Lagrange-Untermannifaltigkeit des T*R^d vorgenommen und diese Objekte werden auf ihre Parametrisierungseigenschaften untersucht. Es stellt sich heraus, dass jedes solche Objekt lokal als die Menge der stationären Punkte einer SG-Phasenfunktion realisiert werden kann.
Als weitere Anwendung werden einige Konstruktionen der axiomatischen Quantenfeldtheorie, die Distributionen beinhalten, im temperierten Kontext realisiert.
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Um esquema de Fourier local para análise tempo-frequência de sinais não-estacionários aplicado a ruído eletroquímico / A scheme for local Fourier analysis time frequency of non-stationary signals applied to the electrochemical noiseFernando Luis Dias 31 July 2014 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Sinais diversos estão presentes em nosso cotidiano, assim como nas medidas
realizadas nas atividades de ciência e tecnologia. Dentre estes sinais, tem grande importância tecnológica aqueles associados à corrosão de estruturas metálicas. Assim,
esta tese propõe o estudo de um esquema local de transformada de Fourier janelada,
com a janela variando em função da curtose, aplicada a sinais de ruído eletroquímico. A
curtose foi avaliada nos domínios do tempo e da frequência e processada pelo programa
desenvolvido para esse fim. O esquema foi aplicado a sinais de ruído eletroquímico
dos aços UNS S31600, UNS G10200 e UNS S32750 imersos em três soluções: FeCl3 0,1
mol=L (cloreto férrico), H2SO4 5%(ácido sulfúrico) e NaOH 0,1%(hidróxido de sódio).
Para os aços inoxidáveis, estas soluções promovem corrosão localizada, uniforme e
passivação, respectivamente. Visando testar o desempenho do esquema de Fourier
desenvolvido, testes foram realizados utilizando-se inicialmente sinais sintéticos e em
seguida sinais de ruído eletroquímico. Notou-se que os sinais têm características de
não-estacionaridade e a maior parte da energia está presente em baixa frequência. Os
intervalos de tempo e de frequência onde se concentra a maior parte da energia do sinal
foram correlacionados. Para os picos máximos dos sinais de potencial e corrente obtidos
de amperimetria de resistência nula, a correlação entre eles foi baixa, independente
da forma de corrosão presente. Conclui-se que o método se adaptou bastante bem às
características locais do sinal eletroquímico permitindo o monitoramento dos espectros
tempo-frequência. O fato de ser sensível às características locais do sinal permite analisar
aspectos dos sinais que do modo clássico não podem ser diretamente processados.
O método da transformada de Fourier janelada variável (Variable Short-Time Fourier
Transform - VSTFT) adaptou-se muito bem no monitoramento dos sinais originados
de potencial de circuito aberto e amperimetria de resistência nula. / Several signals are present in our daily lives, as well as in the measurements
from scientific and technological procedures. Among these signals, it has great technological
importance those associated with corrosion of metallic structures. Thus, this
thesis considers a local windowed Fourier transform, varying according to the kurtosis
of signals, applied to electrochemical noise. The kurtosis was assessed in the kurtosis
of the time and frequency domains and evaluated by the software developed for this
purpose. The scheme has been applied to electrochemical noise signals of UNS S31600,
UNS G10200 and UNS S32750 steels immersed in three solutions: FeCl3 0.1 mol=L
(ferric chloride), H2SO4 5 % (sulfuric acid) and NaOH 0.1 % (sodium hydroxide). For
stainless steels, these solutions cause localized corrosion, uniform corrosion and passivation,
respectively. To test the performance of the proposed Fourier scheme, tests
were conducted initially using synthetic signal and then electrochemical noise signals.
It is worth noticing that the signals have non-stationary characteristics and most part of
its energy is present at low frequency. The time and frequency intervals which concentrate
most part of the energy of the signal were correlated. For the maximum peaks of
the potential and current signals obtained by zero resistance ammeter, the correlation
between them was low, regardless of the form of present corrosion. We conclude that
the method is well adapted to the local features of the electrochemical signal allowing
the monitoring of time-frequency spectograms. As the method is sensitive to the local
features of the sign, it allows to analyse signals that by the classic approach can not
be directly processed. The windowed Fourier transform (Variable Short-Time Fourier
Transform - VSTFT) adapted very well in monitoring of the signals originated by open
circuit potential and zero resistance ammeter.
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Um esquema de Fourier local para análise tempo-frequência de sinais não-estacionários aplicado a ruído eletroquímico / A scheme for local Fourier analysis time frequency of non-stationary signals applied to the electrochemical noiseFernando Luis Dias 31 July 2014 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Sinais diversos estão presentes em nosso cotidiano, assim como nas medidas
realizadas nas atividades de ciência e tecnologia. Dentre estes sinais, tem grande importância tecnológica aqueles associados à corrosão de estruturas metálicas. Assim,
esta tese propõe o estudo de um esquema local de transformada de Fourier janelada,
com a janela variando em função da curtose, aplicada a sinais de ruído eletroquímico. A
curtose foi avaliada nos domínios do tempo e da frequência e processada pelo programa
desenvolvido para esse fim. O esquema foi aplicado a sinais de ruído eletroquímico
dos aços UNS S31600, UNS G10200 e UNS S32750 imersos em três soluções: FeCl3 0,1
mol=L (cloreto férrico), H2SO4 5%(ácido sulfúrico) e NaOH 0,1%(hidróxido de sódio).
Para os aços inoxidáveis, estas soluções promovem corrosão localizada, uniforme e
passivação, respectivamente. Visando testar o desempenho do esquema de Fourier
desenvolvido, testes foram realizados utilizando-se inicialmente sinais sintéticos e em
seguida sinais de ruído eletroquímico. Notou-se que os sinais têm características de
não-estacionaridade e a maior parte da energia está presente em baixa frequência. Os
intervalos de tempo e de frequência onde se concentra a maior parte da energia do sinal
foram correlacionados. Para os picos máximos dos sinais de potencial e corrente obtidos
de amperimetria de resistência nula, a correlação entre eles foi baixa, independente
da forma de corrosão presente. Conclui-se que o método se adaptou bastante bem às
características locais do sinal eletroquímico permitindo o monitoramento dos espectros
tempo-frequência. O fato de ser sensível às características locais do sinal permite analisar
aspectos dos sinais que do modo clássico não podem ser diretamente processados.
O método da transformada de Fourier janelada variável (Variable Short-Time Fourier
Transform - VSTFT) adaptou-se muito bem no monitoramento dos sinais originados
de potencial de circuito aberto e amperimetria de resistência nula. / Several signals are present in our daily lives, as well as in the measurements
from scientific and technological procedures. Among these signals, it has great technological
importance those associated with corrosion of metallic structures. Thus, this
thesis considers a local windowed Fourier transform, varying according to the kurtosis
of signals, applied to electrochemical noise. The kurtosis was assessed in the kurtosis
of the time and frequency domains and evaluated by the software developed for this
purpose. The scheme has been applied to electrochemical noise signals of UNS S31600,
UNS G10200 and UNS S32750 steels immersed in three solutions: FeCl3 0.1 mol=L
(ferric chloride), H2SO4 5 % (sulfuric acid) and NaOH 0.1 % (sodium hydroxide). For
stainless steels, these solutions cause localized corrosion, uniform corrosion and passivation,
respectively. To test the performance of the proposed Fourier scheme, tests
were conducted initially using synthetic signal and then electrochemical noise signals.
It is worth noticing that the signals have non-stationary characteristics and most part of
its energy is present at low frequency. The time and frequency intervals which concentrate
most part of the energy of the signal were correlated. For the maximum peaks of
the potential and current signals obtained by zero resistance ammeter, the correlation
between them was low, regardless of the form of present corrosion. We conclude that
the method is well adapted to the local features of the electrochemical signal allowing
the monitoring of time-frequency spectograms. As the method is sensitive to the local
features of the sign, it allows to analyse signals that by the classic approach can not
be directly processed. The windowed Fourier transform (Variable Short-Time Fourier
Transform - VSTFT) adapted very well in monitoring of the signals originated by open
circuit potential and zero resistance ammeter.
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