964 resultados para Pulse width modulation
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Considers Sampling, Pulse Amplitude Modulation, Multiple Access, Quantisation, Pulse Coded Modulation, Manchester Line Coding, Amplitude Modulation, Double SideBand Suppressed Carrier Modulation, Quadrature Amplitude Modulation and M-ary Shift Keying.
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In this work, we investigate the control of the two-photon absorption process of a series of organic compounds via spectral phase modulation of the excitation pulse. We analyzed the effect of the pulse central wavelength on the control of the two-photon absorption process for each compound. Depending on the molecules` two-photon absorption position relative to the excitation pulse wavelength, different levels of coherent control were observed. By simulating the two-photon transition probability in molecular systems, taking into account the band structure and its positions, we could explain the experimental results trends. We observed that the intrapulse coherent interference plays an important role in the nonlinear process control besides just the pulse intensity modulation.
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A method of unpolarized laser pulses shaping is reported. The basis of the method is the use of an hybrid optical bistable device with nematic liquid-crystals, similar to the one previously reported by us. A sample of the input light constrols, by an asymmetrical electronic comparator, a 1 x 2 electro-optical total switch. The output pulses are reshaped and maintain the same polarization properties as the input light. From triangular input light signals, symmetriacl and asymmetrical output pulses have been obtained. The minimum pulse width achieved was 0.1 msec. A representation of the output versus input light signals gives an hysteresys cycle in the asymmetrical case.
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Esta tesis se centra en el estudio y desarrollo de algoritmos de guerra electrnica {electronic warfare, EW) y radar para su implementacin en sistemas de tiempo real. La llegada de los sistemas de radio, radar y navegacin al terreno militar llev al desarrollo de tecnologas para combatirlos. As, el objetivo de los sistemas de guerra electrnica es el control del espectro electomagntico. Una de la funciones de la guerra electrnica es la inteligencia de seales {signals intelligence, SIGINT), cuya labor es detectar, almacenar, analizar, clasificar y localizar la procedencia de todo tipo de seales presentes en el espectro. El subsistema de inteligencia de seales dedicado a las seales radar es la inteligencia electrnica {electronic intelligence, ELINT). Un sistema de tiempo real es aquel cuyo factor de mrito depende tanto del resultado proporcionado como del tiempo en que se da dicho resultado. Los sistemas radar y de guerra electrnica tienen que proporcionar informacin lo ms rpido posible y de forma continua, por lo que pueden encuadrarse dentro de los sistemas de tiempo real. La introduccin de restricciones de tiempo real implica un proceso de realimentacin entre el diseo del algoritmo y su implementacin en plataformas hardware. Las restricciones de tiempo real son dos: latencia y rea de la implementacin. En esta tesis, todos los algoritmos presentados se han implementado en plataformas del tipo field programmable gate array (FPGA), ya que presentan un buen compromiso entre velocidad, coste total, consumo y reconfigurabilidad. La primera parte de la tesis est centrada en el estudio de diferentes subsistemas de un equipo ELINT: deteccin de seales mediante un detector canalizado, extraccin de los parmetros de pulsos radar, clasificacin de modulaciones y localization pasiva. La transformada discreta de Fourier {discrete Fourier transform, DFT) es un detector y estimador de frecuencia quasi-ptimo para seales de banda estrecha en presencia de ruido blanco. El desarrollo de algoritmos eficientes para el clculo de la DFT, conocidos como fast Fourier transform (FFT), han situado a la FFT como el algoritmo ms utilizado para la deteccin de seales de banda estrecha con requisitos de tiempo real. As, se ha diseado e implementado un algoritmo de deteccin y anlisis espectral para su implementacin en tiempo real. Los parmetros ms caractersticos de un pulso radar son su tiempo de llegada y anchura de pulso. Se ha diseado e implementado un algoritmo capaz de extraer dichos parmetros. Este algoritmo se puede utilizar con varios propsitos: realizar un reconocimiento genrico del radar que transmite dicha seal, localizar la posicin de dicho radar o bien puede utilizarse como la parte de preprocesado de un clasificador automtico de modulaciones. La clasificacin automtica de modulaciones es extremadamente complicada en entornos no cooperativos. Un clasificador automtico de modulaciones se divide en dos partes: preprocesado y el algoritmo de clasificacin. Los algoritmos de clasificacin basados en parmetros representativos calculan diferentes estadsticos de la seal de entrada y la clasifican procesando dichos estadsticos. Los algoritmos de localization pueden dividirse en dos tipos: triangulacin y sistemas cuadrticos. En los algoritmos basados en triangulacin, la posicin se estima mediante la interseccin de las rectas proporcionadas por la direccin de llegada de la seal. En cambio, en los sistemas cuadrticos, la posicin se estima mediante la interseccin de superficies con igual diferencia en el tiempo de llegada (time difference of arrival, TDOA) o diferencia en la frecuencia de llegada (frequency difference of arrival, FDOA). Aunque slo se ha implementado la estimacin del TDOA y FDOA mediante la diferencia de tiempos de llegada y diferencia de frecuencias, se presentan estudios exhaustivos sobre los diferentes algoritmos para la estimacin del TDOA, FDOA y localizacin pasiva mediante TDOA-FDOA. La segunda parte de la tesis est dedicada al diseo e implementacin filtros discretos de respuesta finita (finite impulse response, FIR) para dos aplicaciones radar: phased array de banda ancha mediante filtros retardadores (true-time delay, TTD) y la mejora del alcance de un radar sin modificar el hardware existente para que la solucin sea de bajo coste. La operacin de un phased array de banda ancha mediante desfasadores no es factible ya que el retardo temporal no puede aproximarse mediante un desfase. La solucin adoptada e implementada consiste en sustituir los desfasadores por filtros digitales con retardo programable. El mximo alcance de un radar depende de la relacin seal a ruido promedio en el receptor. La relacin seal a ruido depende a su vez de la energa de seal transmitida, potencia multiplicado por la anchura de pulso. Cualquier cambio hardware que se realice conlleva un alto coste. La solucin que se propone es utilizar una tcnica de compresin de pulsos, consistente en introducir una modulacin interna a la seal, desacoplando alcance y resolucin. ABSTRACT This thesis is focused on the study and development of electronic warfare (EW) and radar algorithms for real-time implementation. The arrival of radar, radio and navigation systems to the military sphere led to the development of technologies to fight them. Therefore, the objective of EW systems is the control of the electromagnetic spectrum. Signals Intelligence (SIGINT) is one of the EW functions, whose mission is to detect, collect, analyze, classify and locate all kind of electromagnetic emissions. Electronic intelligence (ELINT) is the SIGINT subsystem that is devoted to radar signals. A real-time system is the one whose correctness depends not only on the provided result but also on the time in which this result is obtained. Radar and EW systems must provide information as fast as possible on a continuous basis and they can be defined as real-time systems. The introduction of real-time constraints implies a feedback process between the design of the algorithms and their hardware implementation. Moreover, a real-time constraint consists of two parameters: Latency and area of the implementation. All the algorithms in this thesis have been implemented on field programmable gate array (FPGAs) platforms, presenting a trade-off among performance, cost, power consumption and reconfigurability. The first part of the thesis is related to the study of different key subsystems of an ELINT equipment: Signal detection with channelized receivers, pulse parameter extraction, modulation classification for radar signals and passive location algorithms. The discrete Fourier transform (DFT) is a nearly optimal detector and frequency estimator for narrow-band signals buried in white noise. The introduction of fast algorithms to calculate the DFT, known as FFT, reduces the complexity and the processing time of the DFT computation. These properties have placed the FFT as one the most conventional methods for narrow-band signal detection for real-time applications. An algorithm for real-time spectral analysis for user-defined bandwidth, instantaneous dynamic range and resolution is presented. The most characteristic parameters of a pulsed signal are its time of arrival (TOA) and the pulse width (PW). The estimation of these basic parameters is a fundamental task in an ELINT equipment. A basic pulse parameter extractor (PPE) that is able to estimate all these parameters is designed and implemented. The PPE may be useful to perform a generic radar recognition process, perform an emitter location technique and can be used as the preprocessing part of an automatic modulation classifier (AMC). Modulation classification is a difficult task in a non-cooperative environment. An AMC consists of two parts: Signal preprocessing and the classification algorithm itself. Featurebased algorithms obtain different characteristics or features of the input signals. Once these features are extracted, the classification is carried out by processing these features. A feature based-AMC for pulsed radar signals with real-time requirements is studied, designed and implemented. Emitter passive location techniques can be divided into two classes: Triangulation systems, in which the emitter location is estimated with the intersection of the different lines of bearing created from the estimated directions of arrival, and quadratic position-fixing systems, in which the position is estimated through the intersection of iso-time difference of arrival (TDOA) or iso-frequency difference of arrival (FDOA) quadratic surfaces. Although TDOA and FDOA are only implemented with time of arrival and frequency differences, different algorithms for TDOA, FDOA and position estimation are studied and analyzed. The second part is dedicated to FIR filter design and implementation for two different radar applications: Wideband phased arrays with true-time delay (TTD) filters and the range improvement of an operative radar with no hardware changes to minimize costs. Wideband operation of phased arrays is unfeasible because time delays cannot be approximated by phase shifts. The presented solution is based on the substitution of the phase shifters by FIR discrete delay filters. The maximum range of a radar depends on the averaged signal to noise ratio (SNR) at the receiver. Among other factors, the SNR depends on the transmitted signal energy that is power times pulse width. Any possible hardware change implies high costs. The proposed solution lies in the use of a signal processing technique known as pulse compression, which consists of introducing an internal modulation within the pulse width, decoupling range and resolution.
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"November 1966."
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The matched filter detector is well known as the optimum detector for use in communication, as well as in radar systems for signals corrupted by Additive White Gaussian Noise (A.W.G.N.). Non-coherent F.S.K. and differentially coherent P.S.K. (D.P.S.K.) detection schemes, which employ a new approach in realizing the matched filter processor, are investigated. The new approach utilizes pulse compression techniques, well known in radar systems, to facilitate the implementation of the matched filter in the form of the Pulse Compressor Matched Filter (P.C.M.F.). Both detection schemes feature a mixer- P.C.M.F. Compound as their predetector processor. The Compound is utilized to convert F.S.K. modulation into pulse position modulation, and P.S.K. modulation into pulse polarity modulation. The mechanisms of both detection schemes are studied through examining the properties of the Autocorrelation function (A.C.F.) at the output of the P.C.M.F.. The effects produced by time delay, and carrier interference on the output A.C.F. are determined. Work related to the F.S.K. detection scheme is mostly confined to verifying its validity, whereas the D.P.S.K. detection scheme has not been reported before. Consequently, an experimental system was constructed, which utilized combined hardware and software, and operated under the supervision of a microprocessor system. The experimental system was used to develop error-rate models for both detection schemes under investigation. Performances of both F. S. K. and D.P. S. K. detection schemes were established in the presence of A. W. G. N. , practical imperfections, time delay, and carrier interference. The results highlight the candidacy of both detection schemes for use in the field of digital data communication and, in particular, the D.P.S.K. detection scheme, which performed very close to optimum in a background of A.W.G.N.
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We examine the correlations between the parameters of ultra-narrow off-centred filtering and pulse width on the performance of a wavelength paired Nx40Gbit/s DWDM transmission, consisting of carrier suppressed return-to-zero signal with 0.64 bit/s/Hz (without polarization-division multiplexing) spectral efficiency.
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We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 m without pulse compression, external cavity, gain-or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.
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We examine the correlations between the parameters of ultra-narrow off-centred filtering and pulse width on the performance of a wavelength paired Nx40Gbit/s DWDM transmission, consisting of carrier suppressed return-to-zero signal with 0.64 bit/s/Hz (without polarization-division multiplexing) spectral efficiency. 2004 Optical Society of America.
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We experimentally demonstrate pabively Q-switched erbium-doped fiber laser (EDFL) operation using a saturable absorber (SA) based on Fe3O4 nanoparticles (FONPs). As a type of transition metal oxide, the FONPs have a large nonlinear optical response and fast response time. The FONPbased SA pobebes a modulation depth of 8.2% and nonsaturable absorption of 56.6%. Stable pabively Q-switched EDFL pulses with an output pulse energy of 23.76 nJ, a repetition rate of 33.3 kHz, and a pulse width of 3.2 s were achieved when the input pump power was 110mW. The laser features a low threshold pump power of > 15mW.
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Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.
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Au cours des dernires annes, la photonique intgre sur silicium a progress rapidement. Les modulateurs issus de cette technologie prsentent des caractristiques potentiellement intressantes pour les systmes de communication courte porte. En effet, il est prvu que ces modulateurs pourront tre oprs des vitesses de transmission leves, tout en limitant le cot de fabrication et la consommation de puissance. Paralllement, la modulation damplitude multi-niveau (PAM) est prometteuse pour ce type de systmes. Ainsi, ce travail porte sur le dveloppement de modulateurs de silicium pour la transmission de signaux PAM. Dans le premier chapitre, les concepts thoriques ncessaires la conception de modulateurs de silicium sont prsents. Les modulateurs Mach-Zehnder et les modulateurs base de rseau de Bragg sont principalement abords. De plus, les effets lectro-optiques dans le silicium, la modulation PAM, les diffrents types dlectrodes intgres et la compensation des distorsions par traitement du signal sont dtaills.Dans le deuxime chapitre, un modulateur Mach-Zehnder aux lectrodes segmentes est prsent. La segmentation des lectrodes permet la gnration de signaux optiques PAM partir de squences binaires. Cette approche permet dliminer lutilisation de convertisseur numrique-analogique en intgrant cette fonction dans le domaine optique, ce qui vise rduire le cot du systme de communication. Ce chapitre contient la description dtaille du modulateur, les rsultats de caractrisation optique et de la caractrisation lectrique, ainsi que les tests systmes. De plus, les tests systmes incluent lutilisation de pr-compensation ou de post-compensation du signal sous la forme dgalisation de la rponse en frquence pour les formats de modulation PAM-4 et PAM-8 diffrents taux binaires. Une vitesse de transmission de 30 Gb/s est dmontre dans les deux cas et ce malgr une limitation importante de la rponse en frquence suite lajout dun assemblage des circuits radiofrquences (largeur de bande 3 dB de 8 GHz). Il sagit de la premire dmonstration de modulation PAM-8 laide dun modulateur Mach-Zehnder aux lectrodes segmentes. Finalement, les conclusions tires de ce travail ont men la conception dun deuxime modulateur Mach-Zehnder aux lectrodes segmentes prsentement en phase de test, dont les performances montrent un trs grand potentiel. Dans le troisime chapitre, un modulateur rseau de Bragg deux sauts de phase est prsent. Lutilisation de rseaux de Bragg est une approche encore peu dveloppe pour la modulation. En effet, la rponse spectrale de ces structures peut tre contrle prcisment, une caractristique intressante pour la conception de modulateurs. Dans ces travaux, nous proposons lajout de deux sauts de phase un rseau de Bragg uniforme pour obtenir un pic de transmission dans la bande de rflexion de celui-ci. Ainsi, il est possible daltrer lamplitude du pic de transmission laide dune jonction pn. Comme pour le deuxime chapitre, ce chapitre inclut la description dtaille du modulateur, les rsultats des caractrisations optique et lectrique, ainsi que les tests systmes. De plus, la caractrisation de jonctions pn laide du modulateur rseau de Bragg est explique. Des vitesses de transmission PAM-4 de 60 Gb/s et OOK de 55 Gb/s sont dmontres aprs la compensation des distorsions des signaux. notre connaissance, il sagit du modulateur rseau de Bragg le plus rapide ce jour. De plus, pour la premire fois, les performances dun tel modulateur sapprochent de celles des modulateurs de silicium les plus rapides utilisant des microrsonateurs en anneau ou des interfromtres Mach-Zehnder.
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Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.
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Er:YAG laser has been studied as a potential tool for restorative dentistry due to its ability to selectively remove oral hard tissue with minimal or no thermal damage to the surrounding tissues. The purpose of this study was to evaluate in vitro the tensile bond strength (TBS) of an adhesive/composite resin system to human enamel surfaces treated with 37% phosphoric acid, Er:YAG laser (lambda=2.94 mum) with a total energy of 16 J (80 mJ/pulse, 2Hz, 200 pulses, 250 ms pulse width), and Er:YAG laser followed by phosphoric acid etching. Analysis of the treated surfaces was performed by scanning electron microscopy (SEM) to assess morphological differences among the groups. TBS means (in MPa) were as follows: Er:YAG laser + acid (11.7 MPa) > acid (8.2 MPa) > Er:YAG laser (6.1 MPa), with the group treated with laser+acid being significantly from the other groups (p=0.0006 and p= 0.00019, respectively). The groups treated with acid alone and laser alone were significantly different from each other (p=0.0003). The SEM analysis revealed morphological changes that corroborate the TBS results, suggesting that the differences in TBS means among the groups are related to the different etching patterns produced by each type of surface treatment. The findings of this study indicate that the association between Er:YAG laser and phosphoric acid can be used as a valuable resource to increase bond strength to laser-prepared enamel.
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Os efeitos da estimulao ultra-snica sobre a consolidao ssea tm sido demonstrados por trabalhos experimentais e clnicos. Este estudo teve por objetivo investigar a aplicao clnica do ultra-som pulsado de baixa intensidade como tratamento adjuvante de fraturas diafisrias em ces. Foram utilizados 16 ces de raas variadas, com faixa etria entre sete meses e seis anos, peso corpreo entre 2,5 e 43kg, portadores de fraturas diafisrias fechadas recentes localizadas no rdio e ulna, fmur ou tbia e fbula, estabilizadas por procedimentos de osteossntese (fixao esqueltica externa, pinos intramedulares ou a associao desses mtodos). Os ces foram divididos em dois grupos: fraturas estabilizadas tratadas por ultra-som de baixa intensidade (grupo tratado, n=8); fraturas estabilizadas, no tratadas por estimulao ultra-snica, (grupo controle, n=8). Os animais foram avaliados por exames clnicos e radiogrficos nos perodos pr-operatrio, ps-operatrio imediato e a cada 30 dias posteriores aos procedimentos cirrgicos. Realizou-se tratamento com ultra-som pulsado (sinal senoidal com freqncia de 1,5MHz, largura de pulso de 200µs e freqncia de repetio de 1kHz) de baixa intensidade (30mW cm-2), aplicado de modo estacionrio no foco de fratura. A terapia ultra-snica foi realizada 20 minutos por dia, durante 21 dias consecutivos, a partir do perodo compreendido entre o 1° e o 9° dia ps-operatrio. O teste t de Student, empregado na anlise estatstica, mostrou diferena significante (P<0,001 e alfa=0,05) entre as mdias dos parmetros de tempo para consolidao ssea observadas nos animais dos grupos tratado (mdia de 67,5 dias) e controle (mdia de 106 dias). Este protocolo de estimulao ultra-snica promoveu sinais clnicos e radiogrficos acelerados da consolidao ssea nas fraturas tratadas. Os resultados deste estudo sugerem que o ultra-som pulsado de baixa intensidade pode ser indicado como terapia adjuvante de fraturas diafisrias recentes em ces.
