1,487 research outputs found
Sensores de fibra ótica para meios desafiantes
With the present work, the development of fiber optic sensor solutions for the
application in challenging media was intended. New sensor structures based
on the post-processing of optical fibers were addressed, taking into account
their sensitivity to variations in the external environment.
In a first stage, fiber Bragg gratings were embedded in lithium batteries, to
monitor temperature in situ and operando. Due to the harsh chemical
environment of the battery, fiber optic sensors revealed to be the most
advantageous alternative, when comparing to the electronic sensors. Fiber
sensors exhibited good sensitivities and fast responses, besides being less
invasive, thus they did not compromise the battery response. Furthermore, they
were chemically stable.
Still in the framework of this theme, and with the objective of monitoring
possible strain and pressure variations inside the batteries, new sensors based
on in-line Fabry-Perot cavities have been proposed. These sensors were
characterized in lateral load, strain, and temperature.
In a later stage, the study focused on the development of configurations that
allowed to obtain high-resolution and/or sensitivity sensors. One of such
configurations was obtained by creating a hollow microsphere at the fiber tip.
The sensor was used to detected concentration variations and refractive index
of glycerin and water mixtures. The influence of the diaphragm size in the
sensor response was also studied, as well as the temperature response.
New sensors based on multimode interference have also been characterized,
using a coreless silica fiber tip. First, the influence of different parameters, such
as length and diameters were analyzed. The sensors were tested in different
solutions of glucose and water. It was observed that the sensor diameter is a
decisive factor in obtaining devices that are more sensitive to refractive index
and, consequently, to concentration.
The determination of the thermo-optic coefficient of water/ethanol mixtures was
also addressed using a multimode fiber interferometer sensor.
Finally, a multimode interferometer sensor was functionalized by depositing
agarose throughout the structure, allowing to optimize the response of the
sensors to the external environment.Com o presente trabalho pretendeu-se explorar soluções de sensores em fibra
ótica para a aplicação em meios desafiantes. Novas estruturas sensoras
baseadas em pós-processamento de fibra ótica foram abordadas, tendo em
consideração a sua sensibilidade a variações do meio externo.
Numa primeira etapa, foram embebidas redes de Bragg no interior de baterias
de lítio, para monitorizar variações de temperatura in situ e operando. Devido
ao complexo meio químico da bateria, os sensores em fibra ótica revelaram
ser uma alternativa mais vantajosa em relação aos sensores elétricos, não só
pela sensibilidade e rápida resposta, mas também pelo fato de não afetarem o
desempenho da bateria. Além disso, os sensores usados revelaram ser pouco
invasivos e quimicamente estáveis.
Ainda no âmbito deste tema, e com o objetivo de monitorizar possíveis
deformações e variações de pressão no interior da bateria de lítio, foram
desenvolvidos novos sensores baseados em cavidades de Fabry-Perot do tipo
in-line. Esses sensores foram caraterizados em pressão lateral, deformação e
temperatura.
Numa fase posterior, o estudo centrou-se no desenvolvimento de
configurações que permitissem a obtenção de sensores com elevada
resolução e/ou sensibilidade. Uma das configurações consistiu na formação de
uma microesfera oca na ponta de uma fibra ótica. Esse sensor foi utilizado
para detetar variações de concentração e índice de refração de misturas de
glicerina e água. A influência do tamanho do diafragma na resposta do sensor
também foi estudada, assim como a resposta em temperatura.
Em seguida, desenvolveram-se novos sensores baseados em interferência
multimodo, utilizando para tal uma ponta de fibra de sílica sem núcleo. Numa
primeira abordagem analisou-se a influência de diferentes parâmetros, como o
comprimento e o diâmetro dos sensores. Os sensores foram expostos a
diferentes soluções de glucose e água. Verificou-se que o diâmetro do sensor
é um fator decisivo para a obtenção de dispositivos mais sensíveis ao índice
de refração e, consequentemente, à concentração.
Foi também desenvolvido um sensor baseado em interferência multimodo que
permitiu determinar o coeficiente termo-ótico de misturas de etanol e água.
Por fim, procedeu-se à funcionalização de um sensor baseado em interferência
multimodo através da deposição de agarose ao longo da estrutura, permitindo
assim otimizar a sua resposta a variações do meio externo.Programa Doutoral em Engenharia Físic
Interferometric Fiber Optic Sensors
Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair
Dynamic Micromechanical Fabry-Perot Cavity Sensors Fabricated by Multiphoton Absorption Onto Optical Fiber Tips
This research leveraged two-photon polymerization microfabrication to integrate dynamic mechanical components with Fabry-Perot resonators onto the ends of low-loss optical fibers to prototype 3 micro-optic devices. The first device featured a multi-positional mirror that enabled thin-film deposition onto cavities of any length with mirrors of significant curvature, for refractive index sensing. The second device combined an FP cavity with a spring body featuring easily scalable stiffness for pressure sensing. The third device presented a high-speed rotating micro-anemometer for measuring a wide range of gas flows. All devices represent a significant reduction in size and weight over commercially available devices
Desenvolvimento e otimização de sensores em fibra ótica produzidos por laser de femtosegundo
In this work, optical fibre sensors were developed and optimized using a pulsed
femtosecond laser. In addition to the inherent advantages of using femtosecond
pulses, by emitting radiation in the NIR band, it was possible to modify the
refractive index inside dielectric materials, namely silica and polymer optical
fibres.
Prior to the manufacturing of optical structures, a theoretical study was carried
out on the peculiarities of writing-systems based on femtosecond lasers, as well
as on the most common devices inscribed in optical fibres, namely Bragg
gratings, long period gratings, and Fabry-Pérot interferometers.
After assembling femtosecond NIR laser system, Bragg gratings, long period
gratings, Fabry-Pérot interferometers, and interferometers based on the optical
Vernier effect were manufactured using the direct-writing and phase mask
methods. Using the micromachining setup, different structures were created in
already existing optical fibre sensors, namely channels in hollow Fabry-Pérot
cavities and laser etching around Bragg gratings inscribed in polymers optical
fibres. The spectral responses of all devices were extensively characterized to,
mainly, variations of temperature and strain, revealing unique sensitivity values,
especially for the interferometers based on the optical Vernier effect (> 1 nm/°C
and 0.1 nm/µε for temperature and strain, respectively).
To demystify the thermal stability of fibre Bragg gratings, a theoretical and
experimental study was carried out where several Bragg gratings were inscribed
by different techniques, involving different lasers as well as silica and polymer
optical fibres. The experimental results corroborated the theoretical predictions,
where it was concluded that the gratings inscribed by the point-to-point method
using a femtosecond laser have a greater thermal stability and lifetime, even
when subjected to longer and higher temperature regimes.
Finally, a bridge was stablished between the fundamental research developed
during the manufacture of the elementary optical fibre sensors, and possible
applications. Five different sensor concepts were demonstrated and tested,
capable of detecting variations in magnetic fields, fluids refractive index,
temperature, strain and humidity. As results, astonishing sensitivity values were
attained, and several cross-sensitivity problems were mitigated, thus
establishing the foundations for the development of new prototypes for the future.Neste trabalho foram desenvolvidos e otimizados sensores em fibra ótica
através de um laser pulsado de femtosegundo. Para além das vantagens
inerentes de usar pulsos da ordem do femtosegundo, ao emitir radiação na
banda do infravermelho foi possível modificar o índice de refração no interior de
materiais dielétricos, nomeadamente fibras óticas de sílica e polímero.
Antes de proceder ao fabrico das estruturas óticas, foi realizado um estudo
teórico sobre as peculiaridades dos sistemas de escrita baseados em lasers de
femtosegundo, bem como sobre os principais dispositivos inscritos em fibra
ótica, nomeadamente redes de Bragg, redes de período longo, e interferómetros
de Fabry-Pérot.
Após montado o sistema laser NIR de femtosegundo, através de inscrição direta
e por máscara de fase foram fabricadas redes de Bragg, redes de período longo,
interferómetros de Fabry-Pérot, e interferómetros baseados no efeito ótico de
Vernier. Com a montagem de micromaquinação, diferentes estruturas foram
criadas em sensores já existentes, nomeadamente buracos em cavidades
Fabry-Pérot e remoção de material ao redor de redes de Bragg. As respostas
espetrais de todos os dispositivos foram extensivamente caracterizadas,
nomeadamente a variações de temperatura e tensão, revelando elevados
valores de sensibilidades, especialmente para os interferómetros baseados no
efeito ótico de Vernier (> 1 nm/°C e 0.1 nm/µε para temeprature e tensão,
respetivamente).
Para desmistificar a estabilidade térmica de redes de Bragg em fibra ótica, foi
feito um estudo teórico e experimental onde várias redes de Bragg foram
gravadas por diferentes técnicas, envolvendo diferentes lasers e fibras óticas de
sílica e polímero. Os resultados experimentais corroboraram as previsões
teóricas, onde se concluiu que as redes gravadas pelo método de ponto-a-ponto
usando um laser de femtosegundo detêm uma maior estabilidade térmica e
tempo de vida, mesmo quando submetidas a regimes longos de altas
temperaturas.
Por fim, foi feita a ponte entre a investigação fundamental desenvolvida durante
o fabrico de dispositivos elementares em fibras óticas e possíveis aplicações.
Foram demonstrados e testados cinco conceitos diferentes de sensores,
capazes de detetar variações de campos magnéticos, índice de refração de
fluídos, temperatura, tensão e humidade. Foram atingidos valores de
sensibilidade surpreendentes, bem como mitigados problemas de sensibilidade
cruzada, tendo sido assim estabelecidas as fundações para o desenvolvimento
de novos protótipos para o futuro.Programa Doutoral em Engenharia Físic
Optical Harmonic Vernier Effect: A New Tool for High Performance Interferometric Fibre Sensors
The optical Vernier effect magnifies the sensing capabilities of an
interferometer, allowing for unprecedented sensitivities and resolutions to be
achieved. Just like a caliper uses two different scales to achieve higher
resolution measurements, the optical Vernier effect is based on the overlap in
the responses of two interferometers with slightly detuned interference
signals. Here, we present a novel approach in detail, which introduces optical
harmonics to the Vernier effect through Fabry-Perot interferometers, where the
two interferometers can have very different frequencies in the interferometric
pattern. We demonstrate not only a considerable enhancement compared to current
methods, but also better control of the sensitivity magnification factor, which
scales up with the order of the harmonics, allowing us to surpass the limits of
the conventional Vernier effect as used today. In addition, this novel concept
opens also new ways of dimensioning the sensing structures, together with
improved fabrication tolerances.Comment: 19 pages, 8 figures, Published in MDPI Sensor
Femtosecond laser micro-machined optical fiber based embeddable strain and temperature sensors for structural monitoring
Structural monitoring technology is becoming increasingly important for managing all types of structures. Embedding sensors while constructing new structures or repairing the old ones allows for continual monitoring of structural health thus giving an estimate of remaining utility. Along with being embeddable, miniaturized sensors that are easy to handle are highly sought after in the industry where in-situ monitoring is required in a harsh environment (corrosive atmosphere, high temperatures, high pressure etc.).
This dissertation demonstrates the use of femtosecond laser-fabricated Fabry-Perot interferometer (FPI) based optical fiber sensors for embedded applications like structural health monitoring. Two types of Fabry-Perot interferometer sensors, extrinsic FPI and intrinsic FPI, have been designed, developed and demonstrated for strain and temperature monitoring applications. The absence of any movable parts make these sensors easy-to-handle and easy to embed inside a material. These sensors were fabricated using a laboratory integrated femtosecond (fs) laser micromachining system. For the extrinsic Fabry-Perot interferometer (EFPI) design, the fs-laser was used to ablate and remove the material off the fiber end face while for intrinsic Fabry-Perot interferometer (IFPI) design, the laser power was focused inside the fiber on the fiber core to create two microstructures. The scope of the work presented in this dissertation extends to device design, laser based sensor fabrication, sensor performance evaluation and demonstration.
Feasibility of using these sensors for embeddable applications was investigated. A new type of material called Bismaleimide (BMI) was used for demonstrating the embeddability of the sensors. Experimental results of strain and temperature testing are presented and discussed. The EFPI sensor has low temperature sensitivity of 0.59 pm/⁰C and a high strain sensitivity of 1.5 pm/µε. The IFPI sensor has the same strain sensitivity as EFPI but is 25 times more sensitive to the temperature. These sensors were tested up to 850 ⁰C in non-embedded condition and they produced a linear response. A hybrid approach combining the EFPI and IFPI sensors was demonstrated for simultaneous measurement of strain and temperature --Abstract, page iii
Fibre interferometry for differential measurements
This thesis investigates the use of interferometry as an interrogation technology for the measurement of differential length at two widely separate locations. Differential length measurements are essential and can have many applications in industrial processes, therefore accurate measurements can be a critical. Such differential length measurements can be applied to aspects of differential pressure. Using an all optical fibre approach, the research utilises the effects of light interference for both low coherent and high coherent light sources for the determination of a differential length between individual sensing cavities separated by up to 10’s of meters. The construction of the differential length interrogation system makes use of two Fabry-Perot cavities arranged in a tandem configuration, as a means of determining the differential length between them. Such an arrangement provides a common path through which an optical broadband light source at a central wavelength of 1550 nm can propagate. As a consequence of this configuration, differential lengths are made simply using one single measurement, removing the need to determine each individual length. An additional benefit of this common optical path prevents environmental factors such as temperature and air pressures from affecting the measurement length in question. Using a scanning reference Michelson interferometer to induce an optical path change, low coherence interference effects are present when the optical path length of the differential Fabry-Perot cavities is equal to the optical path length difference in the Michelson interferometer. Using a separate DFB laser light source to illuminate the reference interferometer high coherence interference fringes, present when the optical path length of one interferometer arm is changing due to a piezo fibre stretcher, can be analysed to provide an accurate length determination. Taking into consideration the noise within the system the interrogation technique has a length measurement resolution of 27.43 nm. Demonstrations show that a differential length of 82.539 μm could be measured with an uncertainty of 41.00 nm. Through the characterisation of a deformable silicon diaphragm, it would be possible to construct a sensing system capable of measuring a differential pressure of 1 Pa in 100 kPa. This however would require a 9.13 mm thick diaphragm, with a radius of 0.35 m. Such a diaphragm would be out of the question and so further investigation into reducing the length measurement resolution would need to be carried out
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