Free-form optical systems for nonimaging applications : Sistemas ��pticos anam��rficos para aplicaciones anid��licas

La ��ptica anid��lica es una rama de la ��ptica cuyo desarrollo comenz�� a mediados de la d��cada de 1960. Este relativamente nuevo campo de la ��ptica se centra en la transferencia eficiente de la luz, algo necesario en muchas aplicaciones, entre las que destacamos los concentradores solares y los sistemas de iluminaci��n. Las soluciones de la ��ptica cl��sica a los problemas de la transferencia de energ��a de la luz s��lo son adecuadas cuando los rayos de luz son paraxiales. La condici��n paraxial no se cumple en la mayor��a de las aplicaciones para concentraci��n e iluminaci��n. Esta tesis contiene varios dise��os free-form (aquellos que no presentan ninguna simetr��a, ni de rotaci��n ni lineal) cuyas aplicaciones van destinadas a estos dos campos. El t��rmino nonimaging viene del hecho de que estos sistemas ��pticos no necesitan formar una imagen del objeto, aunque no formar la imagen no es una condici��n necesaria. Otra palabra que se utiliza a veces en lugar de nonimaging es la palabra anid��lico, viene del griego "an+eidolon" y tiene el mismo significado. La mayor��a de los sistemas ��pticos dise��ados para aplicaciones anid��licas no presentan ninguna simetr��a, es decir, son free-form (anam��rficos). Los sistemas ��pticos free-form est��n siendo especialmente relevantes durante los ��ltimos a��os gracias al desarrollo de las herramientas para su fabricaci��n como m��quinas de moldeo por inyecci��n y el mecanizado multieje. Sin embargo, solo recientemente se han desarrollado t��cnicas de dise��o anid��licas capaces de cumplir con estos grados de libertad. En aplicaciones de iluminaci��n el m��todo SMS3D permite dise��ar dos superficies free-form para controlar las fuentes de luz extensas. En los casos en que se requiere una elevada asimetr��a de la fuente, el objeto o las restricciones volum��tricos, las superficies free-form permiten obtener soluciones de mayor eficiencia, o disponer de menos elementos en comparaci��n con las soluciones de simetr��a de rotaci��n, dado que las superficies free-form tienen m��s grados de libertad y pueden realizar m��ltiples funciones debido a su naturaleza anam��rfica. Los concentradores anid��licos son muy adecuados para la captaci��n de energ��a solar, ya que el objetivo no es la reproducci��n de una imagen exacta del sol, sino sencillamente la captura de su energ��a. En este momento, el campo de la concentraci��n fotovoltaica (CPV) tiende hacia sistemas de alta concentraci��n con el fin de compensar el gasto de las c��lulas solares multi-uni��n (MJ) utilizadas como receptores, reduciendo su ��rea. El inter��s en el uso de c��lulas MJ radica en su alta eficiencia de conversi��n. Para obtener sistemas competitivos en aplicaciones terrestres se recurre a sistemas fotovoltaicos de alta concentraci��n (HCPV), con factores de concentraci��n geom��trica por encima de 500x. Estos sistemas se componen de dos (o m��s) elementos ��pticos (espejos y/o lentes). En los sistemas presentados a lo largo de este trabajo se presentan ejemplos de concentradores HCPV con elementos reflexivos como etapa primaria, as�� como concentradores con elementos refractivos (lente de Fresnel). Con la necesidad de aumentar la eficiencia de los sistemas HCPV reales y con el fin de proporcionar la divisi��n m��s eficiente del espectro solar, c��lulas conteniendo cuatro o m��s uniones (con un potencial de alcanzar eficiencias de m��s del 45% a una concentraci��n de cientos de soles) se exploran hoy en d��a. En esta tesis se presenta una de las posibles arquitecturas de divisi��n del espectro (spectrum-splitting en la literatura anglosajona) que utilizan c��lulas de concentraci��n comercial. Otro campo de aplicaci��n de la ��ptica nonimaging es la iluminaci��n, donde es necesario proporcionar un patr��n de distribuci��n de la iluminaci��n espec��fico. La iluminaci��n de estado s��lido (SSL), basada en la electroluminiscencia de materiales semiconductores, est�� proporcionando fuentes de luz para aplicaciones de iluminaci��n general. En la ��ltima d��cada, los diodos emisores de luz (LED) de alto brillo han comenzado a reemplazar a las fuentes de luz convencionales debido a la superioridad en la calidad de la luz emitida, elevado tiempo de vida, compacidad y ahorro de energ��a. Los colimadores utilizados con LEDs deben cumplir con requisitos tales como tener una alta eficiencia, un alto control del haz de luz, una mezcla de color espacial y una gran compacidad. Presentamos un colimador de luz free-form con microestructuras capaz de conseguir buena colimaci��n y buena mezcla de colores con una fuente de LED RGGB. Una buena mezcla de luz es importante no s��lo para simplificar el dise��o ��ptico de la luminaria sino tambi��n para evitar hacer binning de los chips. La mezcla de luz ��ptica puede reducir los costes al evitar la modulaci��n por ancho de pulso y otras soluciones electr��nicas patentadas para regulaci��n y ajuste de color. Esta tesis consta de cuatro cap��tulos. Los cap��tulos que contienen la obra original de esta tesis son precedidos por un cap��tulo introductorio donde se presentan los conceptos y definiciones b��sicas de la ��ptica geom��trica y en el cual se engloba la ��ptica nonimaging. Contiene principios de la ��ptica no formadora de imagen junto con la descripci��n de sus problemas y m��todos de dise��o. Asimismo se describe el m��todo de Superficies M��ltiples Simult��neas (SMS), que destaca por su versatilidad y capacidad de controlar varios haces de rayos. Adicionalmente tambi��n se describe la integraci��n K��hler y sus aplicaciones en el campo de la energ��a fotovoltaica. La concentraci��n fotovoltaica y la iluminaci��n de estado s��lido son introducidas junto con la revisi��n de su estado actual. El Segundo y Tercer Cap��tulo contienen dise��os ��pticos avanzados con aplicaci��n en la concentraci��n solar principalmente, mientras que el Cuarto Cap��tulo describe el colimador free-form con surcos que presenta buena mezcla de colores para aplicaciones de iluminaci��n. El Segundo Cap��tulo describe dos concentradores ��pticos HCPV dise��ados con el m��todo SMS en tres dimensiones (SMS3D) que llevan a cabo integraci��n K��hler en dos direcciones con el fin de proporcionar una distribuci��n de irradiancia uniforme libre de aberraciones crom��ticas sobre la c��lula solar. Uno de los dise��os es el concentrador XXR free-form dise��ado con el m��todo SMS3D, donde el espejo primario (X) y la lente secundaria (R) se dividen en cuatro sectores sim��tricos y llevan a cabo la integraci��n K��hler (proporcionando cuatro unidades del array K��hler), mientras que el espejo intermedio (X) presenta simetr��a rotacional. Otro concentrador HCPV presentado es el Fresnel-RXI (FRXI) con una lente de Fresnel funcionando como elemento primario (POE) y una lente RXI como elemento ��ptico secundario (SOE), que presenta configuraci��n 4-fold con el fin de realizar la integraci��n K��hler. Las lentes RXI son dispositivos nonimaging conocidos, pero su aplicaci��n como elemento secundario es novedosa. Los concentradores XXR y FRXI K��hler son ejemplos acad��micos de muy alta concentraci��n (m��s de 2,000x, mientras que los sistemas convencionales hoy en d��a no suelen llegar a 1,000x) preparados para las c��lulas solares N-uni��n (con N>3), que probablemente requerir��n una mayor concentraci��n y alta uniformidad espectral de irradiancia con el fin de obtener sistemas CPV terrestres eficientes y rentables. Ambos concentradores est��n dise��ados maximizando funciones de m��rito como la eficiencia ��ptica, el producto concentraci��n-aceptancia (CAP) y la uniformidad de irradiancia sobre la c��lula libre de la aberraci��n crom��tica (integraci��n K��hler). El Tercer Cap��tulo presenta una arquitectura para la divisi��n del espectro solar basada en un m��dulo HCPV con alta concentraci��n (500x) y ��ngulo de aceptancia alto (���>���1��) que tiene por objeto reducir ambas fuentes de p��rdidas de las c��lulas triple uni��n (3J) comerciales: el uso eficiente del espectro solar y la luz reflejada de los contactos met��licos y de la superficie de semiconductor. El m��dulo para la divisi��n del espectro utiliza el espectro solar m��s eficiente debido a la combinaci��n de una alta eficiencia de una c��lula de concentraci��n 3J (GaInP/GaInAs/Ge) y una de contacto posterior (BPC) de concentraci��n de silicio (Si), as�� como la t��cnica de confinamiento externo para la recuperaci��n de la luz reflejada por la c��lula 3J con el fin de ser reabsorbida por la c��lula. En la arquitectura propuesta, la c��lula 3J opera con su ganancia de corriente optimizada (concentraci��n geom��trica de 500x), mientras que la c��lula de silicio trabaja cerca de su ��ptimo tambi��n (135x). El m��dulo de spectrum-splitting consta de una lente de Fresnel plana como POE y un concentrador RXI free-form como SOE con un filtro paso-banda integrado en ��l. Tanto POE como SOE realizan la integraci��n K��hler para producir homogeneizaci��n de luz sobre la c��lula. El filtro paso banda env��a los fotones IR en la banda 900-1,150nm a la c��lula de silicio. Hay varios aspectos pr��cticos de la arquitectura del m��dulo presentado que ayudan a reducir la complejidad de los sistemas spectrum-splitting (el filtro y el secundario forman una sola pieza s��lida, ambas c��lulas son coplanarias simplific��ndose el cableado y la disipaci��n de calor, etc.). Prototipos prueba-de-concepto han sido ensamblados y probados a fin de demostrar la fabricabilidad del filtro y su rendimiento cuando se combina con la t��cnica de reciclaje de luz externa. Los resultados obtenidos se ajustan bastante bien a los modelos y a las simulaciones e invitan al desarrollo de una versi��n m��s compleja de este prototipo en el futuro. Dos colimadores s��lidos con surcos free-form se presentan en el Cuarto Cap��tulo. Ambos dise��os ��pticos est��n dise��ados originalmente usando el m��todo SMS3D. La segunda superficie ��pticamente activa est�� dise��ada a posteriori como una superficie con surcos. El dise��o inicial de dos espejos (XX) est�� dise��ado como prueba de concepto. En segundo lugar, el dise��o RXI free-form es comparable con los colimadores RXI existentes. Se trata de un dise��o muy compacto y eficiente que proporciona una muy buena mezcla de colores cuando funciona con LEDs RGB fuera del eje ��ptico como en los RGB LEDs convencionales. Estos dos dise��os son dispositivos free-form dise��ados con la intenci��n de mejorar las propiedades de mezcla de colores de los dispositivos no aplan��ticos RXI con simetr��a de revoluci��n y la eficiencia de los aplan��ticos, logrando una buena colimaci��n y una buena mezcla de colores. La capacidad de mezcla de colores del dispositivo no-aplan��tico mejora a��adiendo caracter��sticas de un aplan��tico a su hom��logo sim��trico sin p��rdida de eficiencia. En el caso del dise��o basado en RXI, su gran ventaja consiste en su menor coste de fabricaci��n ya que el proceso de metalizaci��n puede evitarse. Aunque algunos de los componentes presentan formas muy complejas, los costes de fabricaci��n son relativamente insensibles a la complejidad del molde, especialmente en el caso de la producci��n en masa (tales como inyecci��n de pl��stico), ya que el coste del molde se reparte entre todas las piezas fabricadas. Por ��ltimo, las ��ltimas dos secciones son las conclusiones y futuras l��neas de investigaci��n. ABSTRACT Nonimaging optics is a branch of optics whose development began in the mid-1960s. This rather new field of optics focuses on the efficient light transfer necessary in many applications, among which we highlight solar concentrators and illumination systems. The classical optics solutions to the problems of light energy transfer are only appropriate when the light rays are paraxial. The paraxial condition is not met in most applications for the concentration and illumination. This thesis explores several free-form designs (with neither rotational nor linear symmetry) whose applications are intended to cover the above mentioned areas and more. The term nonimaging comes from the fact that these optical systems do not need to form an image of the object, although it is not a necessary condition not to form an image. Another word sometimes used instead of nonimaging is anidolic, and it comes from the Greek ���an+eidolon��� and has the same meaning. Most of the optical systems designed for nonimaging applications are without any symmetry, i.e. free-form. Free-form optical systems become especially relevant lately with the evolution of free-form tooling (injection molding machines, multi-axis machining techniques, etc.). Nevertheless, only recently there are nonimaging design techniques that are able to meet these degrees of freedom. In illumination applications, the SMS3D method allows designing two free-form surfaces to control very well extended sources. In cases when source, target or volumetric constrains have very asymmetric requirements free-form surfaces are offering solutions with higher efficiency or with fewer elements in comparison with rotationally symmetric solutions, as free-forms have more degrees of freedom and they can perform multiple functions due to their free-form nature. Anidolic concentrators are well suited for the collection of solar energy, because the goal is not the reproduction of an exact image of the sun, but instead the collection of its energy. At this time, Concentration Photovoltaics (CPV) field is turning to high concentration systems in order to compensate the expense of multi-junction (MJ) solar cells used as receivers by reducing its area. Interest in the use of MJ cells lies in their very high conversion efficiency. High Concentration Photovoltaic systems (HCPV) with geometric concentration of more than 500x are required in order to have competitive systems in terrestrial applications. These systems comprise two (or more) optical elements, mirrors and/or lenses. Systems presented in this thesis encompass both main types of HCPV architectures: concentrators with primary reflective element and concentrators with primary refractive element (Fresnel lens). Demand for the efficiency increase of the actual HCPV systems as well as feasible more efficient partitioning of the solar spectrum, leads to exploration of four or more junction solar cells or submodules. They have a potential of reaching over 45% efficiency at concentration of hundreds of suns. One possible architectures of spectrum splitting module using commercial concentration cells is presented in this thesis. Another field of application of nonimaging optics is illumination, where a specific illuminance distribution pattern is required. The Solid State Lighting (SSL) based on semiconductor electroluminescence provides light sources for general illumination applications. In the last decade high-brightness Light Emitting Diodes (LEDs) started replacing conventional light sources due to their superior output light quality, unsurpassed lifetime, compactness and energy savings. Collimators used with LEDs have to meet requirements like high efficiency, high beam control, color and position mixing, as well as a high compactness. We present a free-form collimator with microstructures that performs good collimation and good color mixing with RGGB LED source. Good light mixing is important not only for simplifying luminaire optical design but also for avoiding die binning. Optical light mixing may reduce costs by avoiding pulse-width modulation and other patented electronic solutions for dimming and color tuning. This thesis comprises four chapters. Chapters containing the original work of this thesis are preceded by the introductory chapter that addresses basic concepts and definitions of geometrical optics on which nonimaging is developed. It contains fundamentals of nonimaging optics together with the description of its design problems, principles and methods, and with the Simultaneous Multiple Surface (SMS) method standing out for its versatility and ability to control several bundles of rays. K��hler integration and its applications in the field of photovoltaics are described as well. CPV and SSL fields are introduced together with the review on their background and their current status. Chapter 2 and Chapter 3 contain advanced optical designs with primarily application in solar concentration; meanwhile Chapter 4 portrays the free-form V-groove collimator with good color mixing property for illumination application. Chapter 2 describes two HCPV optical concentrators designed with the SMS method in three dimensions (SMS3D). Both concentrators represent K��hler integrator arrays that provide uniform irradiance distribution free from chromatic aberrations on the solar cell. One of the systems is the XXR free-form concentrator designed with the SMS3D method. The primary mirror (X) of this concentrator and secondary lens (R) are divided in four symmetric sectors (folds) that perform K��hler integration; meanwhile the intermediate mirror (X) is rotationally symmetric. Second HCPV concentrator is the Fresnel-RXI (FRXI) with flat Fresnel lens as the Primary Optical Element (POE) and an RXI lens as the Secondary Optical Element (SOE). This architecture manifests 4-fold configuration for performing K��hler integration (4 array units), as well. The RXI lenses are well-known nonimaging devices, but their application as SOE is novel. Both XXR and FRXI K��hler HCPV concentrators are academic examples of very high concentration (more than 2,000x meanwhile conventional systems nowadays have up to 1,000x) prepared for the near future N-junction (N>3) solar cells. In order to have efficient and cost-effective terrestrial CPV systems, those cells will probably require higher concentrations and high spectral irradiance uniformity. Both concentrators are designed by maximizing merit functions: the optical efficiency, concentration-acceptance angle (CAP) and cell-irradiance uniformity free from chromatic aberrations (K��hler integration). Chapter 3 presents the spectrum splitting architecture based on a HCPV module with high concentration (500x) and high acceptance angle (���>���1��). This module aims to reduce both sources of losses of the actual commercial triple-junction (3J) solar cells with more efficient use of the solar spectrum and with recovering the light reflected from the 3J cells��� grid lines and semiconductor surface. The solar spectrum is used more efficiently due to the combination of a high efficiency 3J concentration cell (GaInP/GaInAs/Ge) and external Back-Point-Contact (BPC) concentration silicon (Si) cell. By employing external confinement techniques, the 3J cell���s reflections are recovered in order to be re-absorbed by the cell. In the proposed concentrator architecture, the 3J cell operates at its optimized current gain (at geometrical concentration of 500x), while the Si cell works near its optimum, as well (135x). The spectrum splitting module consists of a flat Fresnel lens (as the POE), and a free-form RXI-type concentrator with a band-pass filter embedded in it (as the SOE), both POE and SOE performing K��hler integration to produce light homogenization. The band-pass filter sends the IR photons in the 900-1,150nm band to the Si cell. There are several practical aspects of presented module architecture that help reducing the added complexity of the beam splitting systems: the filter and secondary are forming a single solid piece, both cells are coplanar so the heat management and wiring is simplified, etc. Two proof-of-concept prototypes are assembled and tested in order to prove filter manufacturability and performance, as well as the potential of external light recycling technique. Obtained measurement results agree quite well with models and simulations, and show an opened path to manufacturing of the Fresnel RXI-type secondary concentrator with spectrum splitting strategy. Two free-form solid V-groove collimators are presented in Chapter 4. Both free-form collimators are originally designed with the SMS3D method. The second mirrored optically active surface is converted in a grooved surface a posteriori. Initial two mirror (XX) design is presented as a proof-of-concept. Second, RXI free-form design is comparable with existing RXI collimators as it is a highly compact and a highly efficient design. It performs very good color mixing of the RGGB LED sources placed off-axis like in conventional RGB LEDs. Collimators described here improve color mixing property of the prior art rotationally symmetric no-aplanatic RXI devices, and the efficiency of the aplanatic ones, accomplishing both good collimation and good color mixing. Free-form V-groove collimators enhance the no-aplanatic device's blending capabilities by adding aplanatic features to its symmetric counterpart with no loss in efficiency. Big advantage of the RXI design is its potentially lower manufacturing cost, since the process of metallization may be avoided. Although some components are very complicated for shaping, the manufacturing costs are relatively insensitive to the complexity of the mold especially in the case of mass production (such as plastic injection), as the cost of the mold is spread in many parts. Finally, last two sections are conclusions and future lines of investigation.

Temperature controlled light-emitting diode lamp for photovoltaic rural applications

In recent years, interest in light-emitting diode (LED) lighting has been growing because of its high efficacy, lifetime and ruggedness. This paper proposes a better adaptation of LED lamps to the technical requirements of photovoltaic lighting domestic systems, whose main quality criteria are reliability and that behave as voltage power supplies. As the key element of reliability in LED lamps is temperature, a solution is proposed for driving LED lamps using voltage sources, such as photovoltaic system batteries, with a control architecture based on pulse width modulation signal that regulates the current applied according to the LED lamp temperature. A prototype of the LED lamp has been implemented and tested to show its good performance at different temperatures and at different battery voltages.

Space-state robust control of a Buck converter with amorphous core coil and variable load

Pulse-width modulation is widely used to control electronic converters. One of the most frequently used topologies for high DC voltage/low DC voltage conversion is the Buck converter. These converters are described by a second order system with an LC filter between the switching subsystem and the load. The use of a coil with an amorphous magnetic material core rather than an air core permits the design of smaller converters. If high switching frequencies are used to obtain high quality voltage output, then the value of the auto inductance L is reduced over time. Robust controllers are thus needed if the accuracy of the converter response must be preserved under auto inductance and payload variations. This paper presents a robust controller for a Buck converter based on a state space feedback control system combined with an additional virtual space variable which minimizes the effects of the inductance and load variations when a switching frequency that is not too high is applied. The system exhibits a null steady-state average error response for the entire range of parameter variations. Simulation results and a comparison with a standard PID controller are also presented.

Online sensorless position estimation for switched reluctance motors using one current sensor

This paper proposes an online sensorless rotor position estimation technique for switched reluctance motors (SRMs) using just one current sensor. It is achieved by first decoupling the excitation current from the bus current. Two phase-shifted pulse width modulation signals are injected into the relevant lower transistors in the asymmetrical half-bridge converter for short intervals during each current fundamental cycle. Analog-to-digital converters are triggered in the pause middles of the dual pulse to separate the bus current for excitation current recognition. Next, the rotor position is estimated from the excitation current, by a current-rise-time method in the current-chopping-control mode in a low-speed operation and a current-gradient method in the voltage-pulse-control mode in a high-speed operation. The proposed scheme requires only a bus current sensor and a minor change to the converter circuit, without a need for individual phase current sensors or additional detection devices, achieving a more compact and cost-effective drive. The performance of the sensorless SRM drive is fully investigated. The simulation and experiments on a 750-W three-phase 12/8-pole SRM are carried out to verify the effectiveness of the proposed scheme.

Wavelet packet decomposition-based fault diagnosis scheme for SRM drives with a single current sensor

Power converters are a key, but vulnerable component in switched reluctance motor (SRM) drives. In this paper, a new fault diagnosis scheme for SRM converters is proposed based on the wavelet packet decomposition (WPD) with a dc-link current sensor. Open- and short-circuit faults of the power switches in an asymmetrical half-bridge converter are analyzed in details. In order to obtain the fault signature from the phase currents, two pulse-width modulation signals with phase shift are injected into the lower-switches of the converter to extract the excitation current, and the WPD algorithm is then applied to the detected currents for fault diagnosis. Moreover, a discrete degree of the wavelet packet node energy is chosen as the fault coefficient. The converter faults can be diagnosed and located directly by determining the changes in the discrete degree from the detected currents. The proposed scheme requires only one current sensor in the dc link, while conventional methods need one sensor for each phase or additional detection circuits. The experimental results on a 750-W three-phase SRM are presented to confirm the effectiveness of the proposed fault diagnosis scheme.

Sistema de armazenamento de energia com base em baterias e no ondulador de tens��o trif��sico

Disserta����o para obten����o do grau de Mestre em Engenharia Electrot��cnica Ramo de Automa����o e Eletrot��cnica Ramo de Automa����o e Eletr��nica Industrial

SVPWM SWITCHING PATTERN FOR Z-SOURCE INVERTER, SIMULATION AND APPLICATION

The voltage source inverter (VSI) and current voltage source inverter (CSI) are widely used in industrial application. But the traditional VSIs and CSIs have one common problem: can���t boost or buck the voltage come from battery, which make them impossible to be used alone in Hybrid Electric Vehicle (HEV/EV) motor drive application, other issue is the traditional inverter need to add the dead-band time into the control sequence, but it will cause the output waveform distortion. This report presents an impedance source (Z-source network) topology to overcome these problems, it can use one stage instead of two stages (VSI or CSI + boost converter) to buck/boost the voltage come from battery in inverter system. Therefore, the Z-source topology hardware design can reduce switching element, entire system size and weight, minimize the system cost and increase the system efficiency. Also, a modified space vector pulse-width modulation (SVPWM) control method has been selected with the Z-source network together to achieve the best efficiency and lower total harmonic distortion (THD) at different modulation indexes. Finally, the Z-source inverter controlling will modulate under two control sequences: sinusoidal pulse width modulation (SPWM) and SVPWM, and their output voltage, ripple and THD will be compared.

HVDC Power Transmission Simulation for Offshore Wind System with Three-Level Converter

An integrated mathematical model for the simulation of an offshore wind system performance is presented in this paper. The mathematical model considers an offshore variable-speed turbine in deep water equipped with a permanent magnet synchronous generator using multiple point full-power clamped three-level converter, converting the energy of a variable frequency source in injected energy into the electric network with constant frequency, through a HVDC transmission submarine cable. The mathematical model for the drive train is a concentrate two mass model which incorporates the dynamic for the blades of the wind turbine, tower and generator due to the need to emulate the effects of the wind and the floating motion. Controller strategy considered is a proportional integral one. Also, pulse width modulation using space vector modulation supplemented with sliding mode is used for trigger the transistors of the converter. Finally, a case study is presented to access the system performance.

Modulation of electrical stimulation applied to human physiology and clinical diagnostic

The use, manipulation and application of electrical currents, as a controlled interference mechanism in the human body system, is currently a strong source of motivation to researchers in areas such as clinical, sports, neuroscience, amongst others. In electrical stimulation (ES), the current applied to tissue is traditionally controlled concerning stimulation amplitude, frequency and pulse-width. The main drawbacks of the transcutaneous ES are the rapid fatigue induction and the high discomfort induced by the non-selective activation of nervous fibers. There are, however, electrophysiological parameters whose response, like the response to different stimulation waveforms, polarity or a personalized charge control, is still unknown. The study of the following questions is of great importance: What is the physiological effect of the electric pulse parametrization concerning charge, waveform and polarity? Does the effect change with the clinical condition of the subjects? The parametrization influence on muscle recruitment can retard fatigue onset? Can parametrization enable fiber selectivity, optimizing the motor fibers recruitment rather than the nervous fibers, reducing contraction discomfort? Current hardware solutions lack flexibility at the level of stimulation control and physiological response assessment. To answer these questions, a miniaturized, portable and wireless controlled device with ES functions and full integration with a generic biosignals acquisition platform has been created. Hardware was also developed to provide complete freedom for controlling the applied current with respect to the waveform, polarity, frequency, amplitude, pulse-width and duration. The impact of the methodologies developed is successfully applied and evaluated in the contexts of fundamental electrophysiology, psycho-motor rehabilitation and neuromuscular disorders diagnosis. This PhD project was carried out in the Physics Department of Faculty of Sciences and Technology (FCT-UNL), in straight collaboration with PLUX - Wireless Biosignals S.A. company and co-funded by the Foundation for Science and Technology.

Direct electrical stimulation using a battery-operated device for induction and modulation of colonic contractions in pigs.

Direct electrical stimulation of the colon offers a promising approach for the induction of propulsive colonic contractions by using an implantable device. The objective of this study was to assess the feasibility to induce colonic contractions using a commercially available battery-operated stimulator (maximum pulse width of 1 ms and maximum amplitude of 10 V). Three pairs of pacing electrodes were inserted into the cecal seromuscular layer of anesthetized pigs. During a first set of in vivo experiments conducted on six animals, a pacing protocol leading to cecum contractions was determined: stimulation bursts with 1 ms pulse width, 10 V amplitude (7-15 mA), 120 Hz frequency, and 30-s burst duration, repeated every 2-5 min. In a second testing phase, an evaluation of the pacing protocol was performed in four animals (120 stimulation bursts in total). By using the battery-operated stimulator, contractions of the cecum and movement of contents could be induced in 92% of all stimulations. A cecal shortening of about 30% and an average intraluminal pressure increase of 10.0 +/- 6.0 mmHg were observed.

Characterising the central mechanisms of sensory modulation in human swallowing motor cortex

Objective: Pharyngeal stimulation can induce remarkable increases in the excitability of swallowing motor cortex, which is associated with short-term improvements in swallowing behaviour in dysphagic stroke patients. However, the mechanism by which this input induces cortical change remains unclear. Our aims were to explore the stimulus-induced facilitation of the cortico-bulbar projections to swallowing musculature and examine how input from the pharynx interacts with swallowing motor cortex. Methods: In 8 healthy subjects, a transcranial magnetic stimulation (TMS) paired-pulse investigation was performed comprising a single conditioning electrical pharyngeal stimulus (pulse width 0.2 ms, 240 V) followed by cortical TMS at inter-stimulus intervals (ISI) of 10-100 ms. Pharyngeal sensory evoked potentials (PSEP) were also measured over the vertex. In 6 subjects whole-brain magnetoencephalography (MEG) was further acquired following pharyngeal stimulation. Results: TMS evoked pharyngeal motor evoked potentials were facilitated by the pharyngeal stimulus at ISI between 50 and 80 ms (�� mean increase: 47��6%, P<0.05). This correlated with the peak latency of the P1 component of the PSEP (mean 79.6��8.5 ms). MEG confirmed that the equivalent P1 peak activities were localised to caudolateral sensory and motor cortices (BA 4, 1, 2). Conclusions: Facilitation of the cortico-bulbar pathway to pharyngeal stimulation relates to coincident afferent input to sensorimotor cortex. Significance: These findings have mechanistic importance on how pharyngeal stimulation may increase motor excitability and provide guidance on temporal windows for future manipulations of swallowing motor cortex. �� 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Acousto-optic modulation of optical reflection properties in fiber Bragg gratings and the application in fiber lasers

This thesis aims to investigate the interaction of acoustic waves and fiber Bragg gratings (FBGs) in standard and suspended-core fibers (SCFs), to evaluate the influence of the fiber, grating and modulator design on the increase of the modulation efficiency, bandwidth and frequency. Initially, the frequency response and the resonant acoustic modes of a low frequency acousto-optic modulator (f < 1.2 MHz) are numerically investigated by using the finite element method. Later, the interaction of longitudinal acoustic waves and FBGs in SCFs is also numerically investigated. The fiber geometric parameters are varied and the strain and grating properties are simulated by means of the finite element method and the transfer matrix method. The study indicates that the air holes composing the SCF cause a significant reduction of the amount of silica in the fiber cross section increasing acousto-optic interaction in the core. Experimental modulation of the reflectivity of FBGs inscribed in two distinct SCFs indicates evidences of this increased interaction. Besides, a method to acoustically induce a dynamic phase-shift in a chirped FBG employing an optimized design of modulator is shown. Afterwards, a combination of this modulator and a FBG inscribed in a three air holes SCF is applied to mode-lock an ytterbium doped fiber laser. To improve the modulator design for future applications, two other distinct devices are investigated to increase the acousto-optic interaction, bandwidth and frequency (f > 10 MHz). A high reflectivity modulation has been achieved for a modulator based on a tapered fiber. Moreover, an increased modulated bandwidth (320 pm) has been obtained for a modulator based on interaction of a radial long period grating (RLPG) and a FBG inscribed in a standard fiber. In summary, the results show a considerable reduction of the grating/fiber length and the modulator size, indicating possibilities for compact and faster acousto-optic fiber devices. Additionally, the increased interaction efficiency, modulated bandwidth and frequency can be useful to shorten the pulse width of future all-fiber mode-locked fiber lasers, as well, to other photonic devices which require the control of the light in optical fibers by electrically tunable acoustic waves.

A high voltage pulse power supply for metal plasma immersion ion implantation and deposition

We describe the design and implementation of a high voltage pulse power supply (pulser) that supports the operation of a repetitively pulsed filtered vacuum arc plasma deposition facility in plasma immersion ion implantation and deposition (Mepiiid) mode. Negative pulses (micropulses) of up to 20 kV in magnitude and 20 A peak current are provided in gated pulse packets (macropulses) over a broad range of possible pulse width and duty cycle. Application of the system consisting of filtered vacuum arc and high voltage pulser is demonstrated by forming diamond-like carbon (DLC) thin films with and without substrate bias provided by the pulser. Significantly enhanced film/substrate adhesion is observed when the pulser is used to induce interface mixing between the DLC film and the underlying Si substrate. (C) 2010 American Institute of Physics. [doi:10.1063/1.3518969]

Solid State Marx Modulator with Blumlein Stack for Bipolar Pulse Generation

Sub-nanosecond bipolar high voltage pulses are a very important tool for food processing, medical treatment, waste water and exhaust gas processing. A Hybrid Modulator for sub-microsecond bipolar pulse generation, comprising an unipolar solid-state Marx generator connected to a load through a stack Blumlein system that produces bipolar pulses and further multiplies the pulse voltage amplitude, is presented. Experimental results from an assembled prototype show the generation of 1000 V amplitude bipolar pulses with 100 ns of pulse width and 1 kHz repetition rate.

Simultaneous determination of nonlinear optical and thermo-optic parameters of liquid samples

The authors apply the theory of photothermal lens formation and also that of pure optical nonlinearity to account for the phase modulation in a beam as it traverses a nonlinear medium. It is used to simultaneously determine the nonlinear optical refraction and the thermo-optic coefficient. They demonstrate this technique using some metal phthalocyanines dissolved in dimethyl sulfoxide, irradiated by a Q-switched Nd:YAG laser with 10 Hz repetition rate and a pulse width of 8 ns. The mechanism for reverse saturable absorption in these materials is also discussed.