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1
Fallon, Richard W. "Fibre Bragg grating strain sensors." Thesis, Aston University, 2000. http://publications.aston.ac.uk/15304/.
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The fabrication of in-fibre Bragg gratings (FBGs) and their application as sensors is reported. The strain and temperature characteristic results for a number of chirped and uniform gratings written into three different host fibres are presented. The static and dynamic temperature response of a commercially available temperature compensated grating is reported. A five sensor wavelength division multiplexed fibre Bragg grating strain measurement system with an interrogation rate of 25 Hz and resolution of 10 was constructed. The results from this system are presented. A novel chirped FBG interrogation method was implemented in both the 1.3 and 1.5 m telecommunication windows. Several single and dual strain sensor systems, employing this method, were constructed and the results obtained from each are reported and discussed. These systems are particularly suitable for the measurement of large strain. The results from a system measuring up to 12 m and with a potential measurement range of 30 m are reported. This technique is also shown to give an obtainable resolution of 20 over a measurement range of 5 000 for a dual sensor system. These systems are simple, robust, passive and easy to implement. They offer low cost, high speed and, in the case of multiple sensors, truly simultaneous interrogation. These advantages make this technique ideal for strain sensing in SMART structures. Systems based on this method have been installed in the masts of four superyachts. A system, based on this technique, is currently being developed for the measurement of acoustic waves in carbon composite panels. The results from an alternative method for interrogating uniform FBG sensors are also discussed. Interrogation of the gratings was facilitated by a specifically written asymmetric grating which had a 15 nm long linearly sloped spectral edge. This technique was employed to interrogate a single sensor over a measurement range of 6 m and two sensors over a range of 4.5 me. The results obtained indicated achievable resolutions of 47 and 38 respectively.
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Brady, Geoffrey Phillip. "Fibre Bragg grating sensors : interrogation and multiplexing techniques." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309781.
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Rigg, Euan. "Fibre Bragg grating sensors for component shape change measurement." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/247.
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Main, Andrew Stuart. "Low-cost interrogation of optical fibre Bragg grating sensors." Thesis, Aston University, 2007. http://publications.aston.ac.uk/8101/.
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Through the application of novel signal processing techniques we are able to measure physical measurands with both high accuracy and low noise susceptibility. The first interrogation scheme is based upon a CCD spectrometer. We compare different algorithms for resolving the Bragg wavelength from a low resolution discrete representation of the reflected spectrum, and present optimal processing methods for providing a high integrity measurement from the reflection image. Our second sensing scheme uses a novel network of sensors to measure the distributive strain response of a mechanical system. Using neural network processing methods we demonstrate the measurement capabilities of a scalable low-cost fibre Bragg grating sensor network. This network has been shown to be comparable with the performance of existing fibre Bragg grating sensing techniques, at a greatly reduced implementation cost.
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Nuttavut, Narin. "Optical fibre sensors based on Bragg grating : an interferometric approach." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396042.
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Bezombes, Frédéric. "Fibre Bragg grating temperature sensors for high-speed machining applications." Thesis, Liverpool John Moores University, 2004. http://researchonline.ljmu.ac.uk/5630/.
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In high-speed grinding research, it is required to measure temperature within the workpiece. Present techniques are thermocouple based, and often suffer from excessive electrical noise on the signal. This thesis presents a number of novel and existing optical sensing devices that overcome this limitation and also, in some cases, offer greater performance. The optical sensors are fibre Bragg grating based and the optical techniques used to interrogate that sensor include DWDM, WDM, athermic grating, tuneable grating and coupler. Optical fibre devices are simpler to place in situ prior to the machining tests and they offer faster response and greater sensitivity than was previously possible. Results are presented from machining tests and the new devices are compared with each other and thermocouple based techniques. A method to relate internal measured temperature to machined surface temperature is also demonstrated in the context of high-speed machining.
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Lloyd, Glynn D. "Resonant cavity Fibre Bragg grating sensor interrogation." Thesis, Aston University, 2004. http://publications.aston.ac.uk/8007/.
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This thesis presents a novel high-performance approach to time-division-multiplexing (TDM) fibre Bragg grating (FBG) optical sensors, known as the resonant cavity architecture. A background theory of FBG optical sensing includes several techniques for multiplexing sensors. The limitations of current wavelength-division-multiplexing (WDM) schemes are contrasted against the technological and commercial advantage of TDM. The author’s hypothesis that ‘it should be possible to achieve TDM FBG sensor interrogation using an electrically switched semiconductor optical amplifier (SOA)’ is then explained. Research and development of a commercially viable optical sensor interrogator based on the resonant cavity architecture forms the remainder of this thesis. A fully programmable SOA drive system allows interrogation of sensor arrays 10km long with a spatial resolution of 8cm and a variable gain system provides dynamic compensation for fluctuating system losses. Ratiometric filter- and diffractive-element spectrometer-based wavelength measurement systems are developed and analysed for different commercial applications. The ratiometric design provides a low-cost solution that has picometre resolution and low noise using 4% reflective sensors, but is less tolerant to variation in system loss. The spectrometer design is more expensive, but delivers exceptional performance with picometre resolution, low noise and tolerance to 13dB system loss variation. Finally, this thesis details the interrogator’s peripheral components, its compliance for operation in harsh industrial environments and several examples of commercial applications where it has been deployed. Applications include laboratory instruments, temperature monitoring systems for oil production, dynamic control for wind-energy and battery powered, self-contained sub-sea strain monitoring.
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Rito, Rodolfo N. L. "Monitoring damage development in composite repairs using chirped fibre Bragg grating sensors." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/808351/.
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Composite repairs are often used for damaged structures in order to recover the mechanical properties of the original structure. During service, there is the possibility that damage will occur in the repaired region and hence it would be useful to be able to monitor such repairs. This research investigates the use of chirped fibre Bragg grating (CFBG) sensors to monitor the development of fatigue damage initiation and growth in the repaired region of three different repair systems, i.e. glass fibre reinforced polymer (GFRP)-to-GFRP scarf repair, GFRP-to-GFRP patch repair and a GFRP patch repair to an aluminium panel. All of these repairs were investigated using a combination of experimental testing and theoretical predictions using finite-element analysis and optical prediction software. For each repair system, the CFBG sensor was embedded in the bond-line during the repair fabrication and the transparency of the GFRP material enabled damage to be observed and recorded. The work began by fatigue loading the GFRP-to-GFRP scarf repair coupon under 4-point bending. The CFBG sensor was embedded in the tensile side of the repair. For this system, the growth of the bond-line cracks could be detected but an accurate determination of the extent of damage was not possible. This was mostly due to the geometry of the scarf repair which led to a high degree of complexity in the interpretation of the data. There was good agreement between the trend of the changes in the spectra in the comparisons of the experimental results and finite-element/optical modelling, although the experimental spectra showed smaller changes than were produced by the modelling. The second repair system investigated was the GFRP-to-GFRP patch repair which was tested in the same way as the scarf repair system. An asymmetric repair was fabricated with the patch being bonded on the tensile face of the coupon. Here, it can be said that growth of the bond-line cracks can be detected using CFBG sensors, and an accurate determination of the current length of the cracks from the spectra was achieved. A explanation of the shift of the low-wavelength end of the spectrum changes with increasing crack growth was provided in terms of strain field change caused by the bond-line cracks. There was good agreement in the comparisons of the experimental results and finite-element/optical modelling. Finally, the third repair system investigated was the patch repair of an aluminium panel which was fatigue loaded in tension. Prior to repair, the aluminium panel was notched at the centre in order to promote crack initiation. Again, an asymmetric repair was fabricated. It can be concluded from the results that the embedded sensor could clearly detect the approach of a fatigue crack and indicate when the crack had passed the location of the sensor. Again, there was good agreement in the comparisons of the experimental results and finite-element/optical modelling. The work has shown that CFBG sensors can be used to monitor damage development in various types of repairs and can give an indication of damage initiation for all of the cases investigated. However, where there is significant geometrical complexity to the repair, as in the case of a scarf repair, detailed interpretation of the spectra in order to extract information on damage growth is much more difficult.
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Dockney, Michael Lee. "Fabrication of wavelength division multiplexed in-fibre Bragg grating arrays for structural monitoring applications." Thesis, Cranfield University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245338.
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Comanici, Maria Iulia. "Interrogation systems for fiber Bragg grating-based sensors." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95079.
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As the potential application of fiber optic sensors broadens, there is much interest in finding measurement systems that are simple, cost effective and show high power efficiency. The latter is extremely useful when dealing with multiplexed sensors distributed over large distances, which results in high signal attenuation and limits the number of sensors that can be interrogated by a minimum number of measurement units. In this thesis we explore a fiber laser-based wavelength-to-power mapping interrogation system for wavelength-division-multiplexed FBG sensors, and we prove that such solution offers increased measurement reliability with high power efficiency. Another aspect of improving the performance of sensing systems is the ability to measure multiple parameters, which are extremely useful when working with FBG-based sensors experiencing similar changes in spectral characteristics in response to changes in temperature or strain. These can be discriminated when they can be measured using different interrogation methods. For this purpose, we first explore and evaluate the performance of a vibration sensor designed by QPS Photronics, and we prove that it can be used to measure temperature and/or strain by translating the changes in its sinusoidal multi-wavelength spectrum to changes in the response of a single pass-band microwave photonic filter (MPF). The operation principle is based on monitoring the shift of the main filter band as temperature or strain changes. We demonstrate that such a system can achieve high-speed measurement with variable sensitivity.Avec la croissance de l'application potentielle des capteurs à fibres optiques, il est important de trouver des systèmes de mesure simples, à coût réduit, et présentant une efficacité de puissance élevée. Celle-ci est extrêmement utile quand il s'agit de multiplexer des capteurs distribués sur des grandes distances, ce qui contribue à l'augmentation de l'atténuation du signal optique et impose une limite au nombre de capteurs qui peuvent être interrogés en utilisant un minimum d'unités de mesure. Dans cette thèse nous explorons un système d'interrogation basé sur un laser à fibre optique pour réaliser la traduction de la longueur d'onde en une mesure de puissance pour les capteurs à base de réseaux de Bragg. Nous prouvons que grâce à cette solution nous pouvons augmenter la fiabilité de la mesure avec une efficacité de puissance élevée ainsi que de réduire les erreurs de la mesure. Pour augmenter la performance d'un système de capteurs, il est aussi important de pouvoir mesurer de paramètres additionnels. Ceci est extrêmement important quand le capteur est base sur des réseaux de Bragg qui ont une réponse similaire aux changements de température ou tension. Ces deux facteurs peuvent être distingués en utilisant des méthodes d'interrogation différentes. Ainsi, nous explorons et évaluons premièrement la performance d'un capteur de vibration conçu par QPS Photronics. Nous prouvons qu'il est possible de mesurer aussi la température et/ou la tension en traduisant les changements du spectre à plusieurs longueurs d'onde en des changements de la réponse d'un filtre à micro-ondes photoniques (MPF) à une seule bande passante. Le principe de l'opération du système est base sur la surveillance du déplacement de la bande passante principale du filtre quand la température ou la tension de la fibre changent. Nous montrons qu'un tel système est capable d'assurer une mesure très rapide avec une sensibilité variable.
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Flockhart, Gordon Marr Henderson. "Interferometric interrogation of optical fibre bragg grating sensors for temperature independent strain measurement." Thesis, Heriot-Watt University, 2001. http://hdl.handle.net/10399/381.
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Mastro, Stephen A. El-Sherif Mahmoud Abd-El-Rahman. "Optomechanical behavior of embedded fiber Bragg grating strain sensors /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/515.
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Schomer, John J. "Embedding fiber Bragg grating sensors through ultrasonic additive manufacturing." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483670362650083.
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Aiyar, Arvind Ramaswamy. "Determination of round exit velocity using fiber Bragg grating sensors." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1398.
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Thesis (M.S.) -- University of Maryland, College Park, 2004.Thesis research directed by: Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Al-Tarawneh, Mu'ath. "Traffic Monitoring System Using In-Pavement Fiber Bragg Grating Sensors." Diss., North Dakota State University, 2019. https://hdl.handle.net/10365/31539.
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Recently, adding more lanes becomes less and less feasible, which is no longer an applicable solution for the traffic congestion problem due to the increment of vehicles. Using the existing infrastructure more efficiently with better traffic control and management is the realistic solution. An effective traffic management requires the use of monitoring technologies to extract traffic parameters that describe the characteristics of vehicles and their movement on the road. A three-dimension glass fiber-reinforced polymer packaged fiber Bragg grating sensor (3D GFRP-FBG) is introduced for the traffic monitoring system. The proposed sensor network was installed for validation at the Cold Weather Road Research Facility in Minnesota (MnROAD) facility of Minnesota Department of Transportation (MnDOT) in MN. A vehicle classification system based on the proposed sensor network has been validated. The vehicle classification system uses support vector machine (SVM), Neural Network (NN), and K-Nearest Neighbour (KNN) learning algorithms to classify vehicles into categories ranging from small vehicles to combination trucks. The field-testing results from real traffic show that the developed system can accurately estimate the vehicle classifications with 98.5 % of accuracy. Also, the proposed sensor network has been validated for low-speed and high-speed WIM measurements in flexible pavement. Field testing validated that the longitudinal component of the sensor has a measurement accuracy of 86.3% and 89.5% at 5 mph and 45 mph vehicle speed, respectively. A performed parametric study on the stability of the WIM system shows that the loading position is the most significant parameter affecting the WIM measurements accuracy compared to the vehicle speed and pavement temperature. Also the system shows the capability to estimate the location of the loading position to enhance the system accuracy.
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Levin, Klas. "Durability of Embedded Fibre Optic Sensors in Composites." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3145.
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SORIA, DARWIN GRAMER FALCON. "MONITORING CORROSION DEFECTS IN PLANAR STRUCTURES WITH FIBER BRAGG GRATING SENSORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19352@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO foco do presente trabalho é a detecção e o monitoramento de defeitos tais como perda de espessura por corrosão ou dano produzido por impacto em painéis metálicos planos. O sistema proposto emprega sensores de deformação a fibra óptica baseados em redes de Bragg, que possuem alta capacidade de multiplexação. O campo de deformações produzido na superfície da placa por um mesmo carregamento, cuja amplitude pode variar, é continuamente comparado a um mapa de referência, obtido com a estrutura íntegra ou na presença um defeito previamente detectado. Variações nos gradientes de deformações são associadas ao surgimento ou crescimento de um ou mais defeitos. Neste estudo, a metodologia foi preliminarmente avaliada através da análise de campos de deformação produzidos por carregamentos de tração em corpos de alumínio contendo defeitos superficiais. Esses defeitos exemplificam danos causados por corrosão, e são monitorados através de sensores a fibra óptica baseados em redes de Bragg. Os sensores são posicionados ao longo de uma das superfícies da placa, medindo deformações em duas direções ortogonais, que neste estudo corresponderam às direções principais de deformação. A abordagem do problema fundamenta-se na análise de dados experimentais e modelagem numérica por elementos finitos. Os resultados numéricos para as deformações são comparados com os obtidos em experimentos em laboratório. A técnica é utilizada para avaliar qualitativamente os defeitos em estruturas submetidas a carregamento estático. A correlação entre resultados numéricos e experimentais mostraram-se satisfatórias, indicando que o método apresenta potencial para ser estendido para aplicações mais complexas.
The present work is focused on detecting and monitoring damage such as loss of thickness due to corrosion or other planar defects in flat metallic panels. The proposed method employs fiber optic sensors that, due to their high multiplexing capability, are capable of mapping the strain fields in the panel surfaces produced by the same, controlled, loading, which are then continuously compared to a reference map obtained with the structure free of defects or with a previously detected damage. Changes in the strain gradient are attributed to the appearance or growth of structural damage. The proposed approach for structural health monitoring has been preliminarily evaluated in this dissertation by analyzing the strain fields produced on an aluminum plate under in plane tensile loads. Artificial, localized surface defects, simulating a loss of thickness due to corrosion where the investigated defects. A mesh of fiber Bragg grating sensors was installed on one of the panel surfaces measuring its principal strains. The strain fields obtained with the plate containing defects with different depths and sizes were compared to a reference measurement with the panel without defects. Experimental data was compared with numerical simulations based on the Finite Element method. The correlation between numerical and experimental results was satisfactory indicating that the method can be further developed in order to be applied in implementations of structural health monitoring systems.
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Al-Tarawneh, Mu’ath Ahmad. "In-Pavement Fiber Bragg Grating Sensors for Weight-In-Motion Measurements." Thesis, North Dakota State University, 2016. https://hdl.handle.net/10365/28248.
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Estimation a traffic over the design period is one of the critical factors in pavement design. Weight-in-motion (WIM) sensors have become popular for weight measurements. A three-dimension glass fiber-reinforced polymer packaged fiber Bragg grating sensor (3D GFRP-FBG) is introduced for in-pavement WIM measurement at low speed. Sensitivity study shows that the sensor is very sensitive to the sensor installation depth and the loading position. The developed 3D GFRP-FBG sensor is applicable for most practical pavements and it also shows a very good long-term durability. Among the three components of the sensor, the longitudinal component has the highest sensitivity for WIM measurements. Field testing results indicated that the 3D GFRP-FBG sensor has a measurement accuracy of 90%, 79%, and 67% for longitudinal, transverse, and vertical components, respectively. Thus, it is recommended to use the longitudinal sensing unit if only one dimension of the sensor is to be further advanced for practice.
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Cooper, David J. F. "Time division multiplexing of a serial fibre optic Bragg grating sensor array." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0001/MQ45424.pdf.
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Hu, Di. "Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85112.
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A fully distributed multi-parameter acoustic sensing technology is proposed. Current fully distributed sensing techniques are exclusively based on intrinsic scatterings in optical fibers. They demonstrate long sensing span, but their limited applicable parameters (temperature and strain) and costly interrogation systems have prevented their widespread applications.
A novel concept of acoustic fiber Bragg grating (AFBG) is conceived with inspiration from optical fiber Bragg grating (FBG). This AFBG structure exploits periodic spatial perturbations on an elongated waveguide to sense variations in the spectrum of an acoustic wave. It achieves ten times higher sensitivity than the traditional time-of-flight measurement system using acoustic pulses. A fast interrogation method is developed to avoid frequency scan, reducing both the system response time (from 3min to <1ms) and total cost.
Since acoustic wave propagates with low attenuation along varieties of solid materials (metal, silica, sapphire, etc.), AFBG can be fabricated on a number of waveguides and to sense multiple parameters. Sub-millimeter metal wire and optical fiber based AFBGs have been demonstrated experimentally for effective temperature (25~700 degC) and corrosion sensing. A hollow borosilicate tube is demonstrated for simultaneous temperature (25~200 degC) and pressure (15~75 psi) sensing using two types of acoustic modes. Furthermore, a continuous 0.6 m AFBG is employed for distributed temperature sensing up to 500 degC and to accurately locate the 0.18 m long heated section.
Sensing parameters, sensitivity and range of an AFBG can be tuned to fit a specific application by selecting acoustic waveguides with different materials and/or geometries. Therefore, AFBG is a fully distributed sensing technology with tremendous potentiality.Ph. D.
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Mulvihill, Paul. "Manufacturing optical fibre Bragg grating strain sensors with an excimer laser for high-strain, multiplexed embedded applications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq29369.pdf.
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Morana, Adriana. "Gamma-rays and neutrons effects on optical fibers and Bragg gratings for temperature sensors." Phd thesis, Université Jean Monnet - Saint-Etienne, 2013. http://tel.archives-ouvertes.fr/tel-01064993.
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The nuclear industry shows an increasing interest in the fiber optic technology for both data communication and sensing applications in nuclear plants. The optical fibers offer several advantages and the sensors based on this technology do not need any electrical power at the sensing point, they have a quick response and they can be easily multiplexed: in the case of a temperature sensor, several thermocouples can be substituted by a single fiber, resulting in a decrease of the waste material. The fission reactors are a very harsh environment: it is characterized by the highest dose of gamma-rays, of the order of magnitude of GGy, besides a high flux of neutrons and high operating temperature (300°C for the current reactors, known as generation III). This work has been carried out in collaboration with AREVA, a French industrial conglomerate active in the energy domain, with the aim of realizing a temperature sensor resistant to the environment of nuclear reactor of generation IV, in particular a Sodium-cooled Fast Reactor. The currently used technology, the thermocouples, presents a drift of the measurement due to irradiation, that needs a calibration, and a long response time on the order of seconds. In order to remove the drift, to reduce the response time and to increase the precision, a Fiber Bragg Grating temperature sensor was chosen, in regard to all the advantages of the optical fibers. To understand the behavior of such system in a harsh environment, as the nuclear reactor core, we used an experimental approach based on complementary techniques such as radiation-induced attenuation, photoluminescence, electron paramagnetic resonance and Raman spectroscopies
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Liu, Weilin. "Real-time Interrogation of Fiber Bragg Grating Sensors Based on Chirped Pulse Compression." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20289.
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Theoretical and experimental studies of real-time interrogation of fiber Bragg grating (FBG) sensors based on chirped pulse compression with increased interrogation resolution and signal-to-noise ratio are presented. Two interrogation systems are proposed in this thesis.
In the first interrogation system, a linearly chirped FBG (LCFBG) is employed as the sensing element. By incorporating the LCFBG in an optical interferometer as the sensor encoding system, employing wavelength-to-time mapping and chirped pulse compression technique, the correlation of output microwave waveform with a chirped reference waveform would provide an interrogation result with high speed and high resolution. The proposed system can provide an interrogation resolution as high as 0.25 μ at a speed of 48.6 MHz. The second interrogation system is designed to achieve simultaneous measurement of strain and temperature. In this system, a high-birefringence LCFBG (Hi-Bi LCFBG) is employed as a sensing element.
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Capell, Tobias F. "Applications of embedded chirped fibre Bragg grating sensors for damage and defect detection in composites and composite bonded joints." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580337.
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This thesis reports investigations into the application of a type of optical sensor to detect and monitor damage in composites structures. The chirped fibre Bragg grating (CFBG) is a type of optical component that is sensitive to both strain and temperature and is commonly found in the telecommunications industry as a filter. Its small diameter and low cost makes it a potentially inexpensive sensor ideal for embedding in composite materials. This work consisted of extending the use of CFBG sensors into three areas: monitoring of disbonding in composite-metal bonded joints; detection of manufacturing defects in composite-composite bonded joints; monitoring of delamination lengths for a specimen subjected to mode II loading. All of these areas were investigated using a combination of experimental testing and theoretical predictions (using finite element analysis and optical prediction software). The first area investigated used a bonded joint composed of one metal adherend (aluminium) and one composite adherend with an embedded CFBG, bonded together at elevated temperature. Thermal strains were generated in the bonded joint on cooling the joint from the adhesive cure temperature to room temperature. The joint was then subject to tension-tension fatigue loading, which caused the joint to progressively disbond. The relaxation of the thermal strain in the composite adherend due to the advancing disbond front caused perturbations in the reflected spectra from the embedded CFBG sensor which allowed the development of the disbond to be tracked to within about 2 mm. In the second area, CFBG sensors were embedded within one of the composite adherends in a composite-composite bonded joint with an included manufacturing defect in the bondline. The first defect used was PTFE and the reflected spectrum from the CFBG sensor showed a clear perturbation at the defect location (the joint was externally loaded). Subsequent tests used more realistic defects (i.e. "air gaps" introduced into the bond) as the defect, and perturbations were observed in the CFBG spectra for both glass fibre reinforced plastic (GFRP-GFRP) joints and carbon fibre reinforced plastic (CFRP-CFRP) bonded joints. The effect of defect size and position was also investigated. The results for detecting the air defects were not as clear as for the PTFE artificial defect; however defects of 5 mm or longer could be detected at any position within the joints. The third area investigated in this work used embedded CFBGs to monitor delamination lengths in specimens subjected to mode II loading. A CFRP End-notch flexure specimen (ENF) was modelled using finite element analysis and predictions were made of the reflected CFBG spectra to establish the effect of sensor position on the reflected spectra. ENF specimens were then manufactured with sensors embedded in the positions which would produce the clearest perturbations (based on the computer modelling). Delaminations were grown in the ENF specimens and the effects on the reflected spectra were compared with the predictions, with excellent agreement between the extension of the delaminations as monitored directly and by the CFBG sensors, but only when low-reflectivity sensors (i.e. 40% reflectivity) were used. Indeed, a very important and supplementary part of the delamination study showed that sensor sensitivity to non-uniform strain fields (i.e. the type of strain distribution generated by damage in composite materials) is increased with decreasing CFBG reflectivity
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Molony, Anna. "The application of fibre Bragg grating networks as strain sensors and as phased array antenna true time delay elements." Thesis, Aston University, 1996. http://publications.aston.ac.uk/15355/.
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The fabrication of in-fibre Bragg gratings, and the application of arrays of such gratings as strain sensors and as true time delay elements for the control of phased array antennas is reported. Chirped period Bragg gratings were produced using the fibre deformation fabrication technique, with chirps of between 2.9nm and 17.3nm achieved. Arrays of 5mm and 2mm long uniform period Bragg gratings were fabricated using the inscription method, for use as true time delay elements,dissimilar wavefronts and their spectral characteristics recorded. The uniform period grating arrays were used to create minimum time delays of 9.09ps, 19.02ps and 31ps; making them suitable for controlling phased array antennas operating at RF frequencies of up to 3GHz, with 10° phase resolution. Four 4mm long chirped gratings were produced using the dissimilar wavefronts fabrication method, having chirps of 7nm, 12nm, 20nm and 30nm, and were used to create time delays of between 0.3ps and 59ps. Hence they are suitable for controlling phased array antennas at RF frequencies of up to 48GHz. The application of in fibre Bragg gratings as strain sensors within smart structure materials was investigated, with their sensitivity to applied strain and compression measured for both embedded and surface mounted uniform period and fibre Fabry-Perot filter gratings. A fibre Bragg grating sensor demultiplexing scheme based on a liquid crystal filled Fabry-Perot etalon tuneable transmission filter was proposed, successfully constructed and fully characterised. Three characteristics of the LCFP etalon were found to pose operational limitations to its application in a Bragg grating sensor system; most significantly, the resonance peak wavelength was highly (-2,77nm/°C) temperature dependent. Several methods for minimising this temperature sensitivity were investigated, but enjoyed only limited success. It was therefore concluded that this type (E7 filled) of LCFP etalon is unsuitable for use as a Bragg grating sensor demultiplexing element.
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Reeves, Richard John. "Demodulation and de-multiplexing of a fibre Bragg grating sensor array using volume holograms." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4461.
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The demodulation of a Wavelength Division Multiplexed FBG sensor array by a matching array of holograms hosted within a Volume Holographic (VH) material is considered within this thesis. The FBG sensor elements possess separate quiescent wavelengths and operate within different wavelength ranges. The edge of the transfer function of the demodulating holographic element is aligned with the operating range of the matching sensor element. The holographic element then diffracts a fraction of the sensor signal depending on its instantaneous wavelength. The signals from each of the sensor elements are also diffracted through separate angles to matching detectors so de-multiplexing the sensor array.
A scheme using narrow bandwidth holographic transfer functions to demodulate a two element strain sensor array fabricated 4nm apart is reported. The transfer functions and the hysteresis within the PZT actuator, applying the strain, are represented mathematically and used to process results. These are compared with a normalised saw-tooth voltage waveform applied to the PZT to achieve a high Pearson correlation factor of 0.9992. The holograms however possessed poor diffraction efficiency <1% so severely degrading strain resolution. The crosstalk between the sensors’ channels is measured as -8.3dB.
The demodulation scheme is intensity based so is susceptible to fluctuations in source intensity and fibre bend losses. An intensity reference scheme is therefore demonstrated using two holograms to demodulate a single FBG strain sensor. The sensor’s signal is divided by the two holograms and the intensity of the respective parts recorded on matched photo-detectors. Ratiometric detection is then used to identify changes in applied strain while disregarding fluctuations in source intensity and fibre bend losses. The standard difference over sum equation for ratiometric detection however is modified to take account of the respective holographic transfer functions.
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Propst, Adam Christopher. "Damage Monitoring in Woven Composites Using Fiber-Bragg Grating Sensors on Multiple Time Scales." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-04252009-090648/.
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This study investigates the application of Fiber Bragg Grating (FBG) optical sensors interrogation techniques over several time scales to monitor damage in composite structures due to low velocity impacts events. Optical fiber sensors are embedded into carbon fiber/epoxy resin woven composites using a single-step cure process. The composite specimens are subjected to multiple low energy impacts until failure. Impact events are characterized by acceleration and position sensors integral to the impactor head. The embedded FBG sensors are interrogated using three different interrogation techniques. Low speed, full spectrum measurements are recorded using a tunable laser source. High speed, peak wavelength detection data is taken using a commercial peak wavelength interrogation system. Finally, high speed full spectrum measurements are recorded using new instrumentation developed at Brigham Young University. By qualitatively examining the responses of these three techniques and comparing the FBG data with impact characterization data, a more complete picture of the composite health is available.
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Sans, Canovas Daniel. "Advances in fibre Bragg grating sensors for damage detection in composite laminates: application in quasi-static and fatigue delamination tests." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/117357.
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The use of composite materials in industrial applications such as aeronautical, aerospace or wind energy production has greatly increased in recent decades. Due to their inherent properties, these materials allow lighter, larger and more resistant structures. However, the use of composite materials for components or structures with highly stringent requirements, is hampered by the lack of knowledge of their reliability. In this thesis, some fundamental aspects about the use of fibre Bragg grating (FBG) sensors for internal strain measurements in composite laminates are discussed. In addition, a highly accurate method for locating the crack tip position in mixed-mode delamination growth has been presented. Finally, an experimental application of FBGs to dynamic measurements in mode I fatigue test has been performedL’ús de materials compostos en aplicacions de caràcter industrial com per exemple l’aeronàutica, aeroespacial o la de producció d’energia eòlica, ha crescut exponencialment durant les últimes dècades. Degut a les seves extraordinàries propietats, l’ús d’aquests materials permet la construcció d’estructures més lleugeres, grans i resistents, tot i que el seu ús en components d’alta responsabilitat estructural està limitat per la manca de coneixement en relació a la seva fiabilitat estructural. En aquesta tesi es discuteixen alguns aspectes significants sobre l’ús de FBGs per a mesurar camps de deformació en l’interior de laminats de material compòsit, s’ha analitzat també la capacitat de localització de la punta d’una esquerda en creixement de mode mixt i per últim s’ha desenvolupat una aplicació pràctica dels FBG en temps real en assaigs a fatiga en mode I
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Pfeiffer, Frank. "Einfluß ionisierender Strahlung auf die Funktionsfähigkeit faseroptischer Bragg-Gitter-Sensoren - Influence of ionizing radiation on the operativeness of fiber-optic Bragg-grating sensors." Gerhard-Mercator-Universitaet Duisburg, 2001. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-05252001-105026/.
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Fiber-optic Bragg-Grating sensors are often the only possibility to perform measurements under adverse environmental conditions, ionizing radiation among them. However, up to now no basic research has been carried out to determine the influence of ionizing radiation on the operativeness of Bragg-Grating-Sensors. Within this work gratings of type I have been written into 3 different singlemode-fibers, with different Ge-content, one of them hydrogen-loaded. Various kinds of ionizing radiation (electrons, photons, He-nuclei) of various energy have been applied to the gratings and grating-temperature-sensors with doses up to 90 MGy. Changees of grating-properties have been monitored before and after irradiation. Experiments show only slight increase of the Bragg-wavelength within the measurement-precision of 1E-03 nm. According to these changes which were also estimated by theoretical considerations, typical applications for grating-sensors with exposure to ionizing radiation have been examinded to tell whether the sensors will meet the specific demands of the respective application.
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Espejo, Robert Joseph. "Low coherence interferometry: Applications to component metrology and high spatial resolution fiber Bragg grating sensors." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3308677.
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OLIVIERI, BRUNO SAPHA. "INTERROGATION SYSTEM OF FIBER BRAGG GRATING SENSORS USING TIME DIVISION MULTIPLEXING AND WAVELENGTH DIVISION MULTIPLEXING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5905@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORUm sistema de interrogação de sensores a rede de Bragg utilizando multiplexação no tempo e multiplexação no comprimento de onda é proposto e demonstrado. O sistema apresenta uma solução para a medição de grandezas associadas ao espectro de reflexão de redes de Bragg, possibilitando o aumento do número de sensores a rede de Bragg monitorados através de grandes distâncias em uma mesma fibra óptica, sem um aumento significativo dos custos. O aspecto inovador deste sistema reside na particular associação das seguintes características: o uso de fonte pulsada de banda larga, a disposição, em série, de um grande número de sensores a rede de Bragg de baixa refletividade, a técnica de reutilização dos mesmos comprimentos de onda nominais em grupos contendo vários sensores com comprimentos de onda nominais distintos e um processo de filtragem espectral e análise de sinais pulsados utilizando o filtro DWDM comercial. Aspectos teóricos e experimentais considerando os princípios de trabalho desta técnica são discutidos. Comparações entre resultados simulados e experimentais do sistema implantado mostram boa concordância. Resultados experimentais apontam uma faixa dinâmica de 1,7 nm, podendo encontrar aplicações em medição de temperatura com uma faixa de 150°C. Incertezas com valores médios abaixo de 20 picometros foram obtidas. Simulações experimentais apontam a possibilidade de utilização de um número de aproximadamente 70 sensores com 0,4% de refletividade, por comprimento de onda. Considerando a largura de banda do dispositivo DWDM (1539- 1565 nm) utilizado neste sistema, e um espaçamento de 7 nm por comprimento de onda nominal de sensor, extrapolações mostram que este número pode chegar a 210 sensores em três diferentes comprimentos de onda nominais de sensor. Considerando as bandas C e L este número pode chegar a aproximadamente 1000 sensores em 14 diferentes comprimentos de onda nominais de sensor.
An interrogation system of fiber Bragg grating sensors using time division multiplexing and wavelength division multiplexing is proposed and demonstrated. The system presents a solution to measure the magnitudes associated to the reflection spectrum of the fiber Bragg gratings, making possible to increase the number of the Bragg gratings sensors monitored through large distances at the same fiber optic, without a great increase in the costs. The innovative aspect of this system is the particular association of the following characteristics: the use of a pulsed broad band source, the disposition, in series, of a large number of low reflectivity Bragg gratings sensors, the reusing technique of the same nominal wavelengths in groups containing several numbers of sensors with distinct nominal wavelengths, and a spectral analyzing and filtering process of pulsed signals using a commercial DWDM filter. Theoretical and experimental aspects regarding the working principles of this technique are discussed. Comparisons between experimental and simulated results show a good agreement. Experimental results indicate that a dynamic range of 1,7 nm was obtained. It can be used in temperature measurement systems, with a 150°C range. Uncertainties equivalent to approximately 20 picometers was obtained. Experimental simulations indicate that it would be possible to use a number of approximately 70 sensors with 0,4% reflectivity at each nominal sensor wavelength. Considering the DWDM filter bandwidth (1539-1565 nm) used in this system, and a spectral separation of 7 nm by nominal sensor wavelength, extrapolations indicate that a number of 210 sensors can be obtained, in three different nominal sensor wavelength. Using the C-band and the L-band, a number of 1000 sensors can be obtained, in fourteen different nominal sensor wavelength.
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LOUZADA, DANIEL RAMOS. "DETECTION AND CHARACTERIZATION OF STRUCTURAL DAMAGE USING FIBER BRAGG GRATING SENSORS AND ARTIFICIAL NEURAL NETWORKS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=37156@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
O aumento dos custos relacionados aos processos de manutenção em estruturas como aeronaves, aliadas à crescente demanda das mesmas, alimentam a necessidade de investimentos em técnicas inovadoras de monitoramento estrutural. Dessa forma, o trabalho realizado nesta tese, busca o desenvolvimento de uma técnica de monitoramento ativo, visando o acompanhamento de parâmetros da estrutura analisada, a fim de identificar e caracterizar processos de dano não visíveis, tais como corrosão e delaminação. A metodologia empregada, teve como base a análise dos padrões de deformação superficial, obtidos com o uso de grades de sensores à fibra óptica baseadas em redes de Bragg (FBG). Inicialmente, tais padrões foram provocados por carregamentos estáticos (tração), e posteriormente por atuadores PTZ fixados à estrutura. Estes últimos são submetidos a uma voltagem alternada e frequência fixa. Esta técnica apresenta todas as vantagens dos sensores FBG (massa e dimensões reduzidas, imunidade eletromagnética, elevado poder de multiplexação e alta sensibilidade entre outras), alem de permitir a visualização de alterações nos padrões de deformação, provocados por danos, através da variação da frequência de excitação. Com relação à interpretação dos resultados, a estratégia empregada consistiu em separar o problema de detecção e caracterização dos danos. Dessa forma, a detecção é realizada comparando a energia das deformações superficiais dos corpos de prova nos casos com e sem defeito, enquanto a caracterização é obtida através a utilização de redes neurais artificiais (RNA), por meio de rotinas de reconhecimento de padrões.
The higher costs related to maintenance processes in structures such as aircraft, coupled with the growing demand of them, fueling the need for investment in innovative techniques for structural monitoring. Thus, the work done in this thesis seeks to develop a technique of active monitoring, aiming at monitoring of structure parameters analyzed in order to identify and characterize processes of hidden damage such as corrosion and delamination. The maid methodology was based on the analysis of patterns of surface deformation, obtained with the use of nets of optical fiber sensors based on fiber Bragg gratings ( FBG ). Initially, these patterns were caused by static loads (tension ), and later by PTZ actuators fixed to the frame, who are subjected to an AC voltage and fixed frequency. This technique has all the advantages of the FBG s sensors (mass and small dimensions, electromagnetic immunity, high multiplexing s power and high sensitivity among others), in addition to allowing visualization of changes in the patterns of deformation caused by damage, by varying the frequency excitation. With respect to the interpretation of the results, the strategy employed was to separate the problem of detection and characterization of damage. Thus, the detection is performed by comparing the deformation energy of the surface of the specimens in the cases with and without defect, whereas the characterization is obtained through the use of artificial neural networks (ANN) by means of pattern recognition routines.
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Chilelli, Sean Kelty. "Structural health monitoring with fiber Bragg grating sensors embedded into metal through ultrasonic additive manufacturing." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563529169604482.
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Müller, Uwe Christian [Verfasser]. "Structural Monitoring and Displacement Field Estimation based on Distributed Fiber Bragg Grating Sensors / Uwe Christian Müller." München : Verlag Dr. Hut, 2011. http://d-nb.info/1011441764/34.
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CRUZ, HUGO ANGEL BARREDA DE LA. "ANALYSIS OF THE CALIBRATION TO BRAGG GRATING SENSORS IN FIBER OPTICS INTERROGATED TROUGHT FIXED FILTERS TECHNIQUE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11923@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORNesse trabalho, descreve-se o desenvolvimento de uma calibração do sistema de interrogação dos espectros das redes de Bragg baseando-se em uma simulação numérica adotada de testes experimentais. O objetivo é calibrar a técnica de demodulação óptica utilizando dois filtros de transmissão fixos, procurando-se principalmente a posição verdadeira dos sensores. O espectro refletido de uma rede tem uma forte dependência com o espectro da luz incidente que resultará em uma deformação no espectro refletido da rede, gerando um desvio no sensor detectado. A metodologia é gerar uma perturbação na fonte de luz e analisar a leitura do espectro da rede. Esse desvio gerado na leitura espectral é associado à potência óptica lida nos fotodetectores com a posição do comprimento de onda do sensor; as leituras indicadas são proporcionais ao grau de superposição entre os espectros do sensor e dos filtros. A calibração é enfatizada em simulações comparando-se com resultados experimentais e será recuperado principalmente o espectro deformado da rede por um espectro indicado que fornecerá a informação correta da posição do sensor. A simulação conclui em uma recuperação do espectro deformado, diminuindo incertezas de medição e da posição do sensor comparando-se com medidas experimentais proporcionando bons resultados.
The development of a calibration system for Fiber Bragg Grating sensors based on two fixed spectral filters has been described basing in adopted numeric simulation of experimental tests. The objective is to gage the technique of optical demodulação using two fixed transmission filters, being sought mainly the true position spectral of sensors. The reflected spectrum of a Bragg Grating has a strong dependence with the spectrum of the incident light that will result in a deformation to the reflected spectrum, generating a deviation in the sensor detected. The methodology will be to generate a disturbance in the light source and to analyze the reading of the spectrum Bragg Grating. That deviation in the position is associated to the potency optical work in the photodetectors with the position of wavelength sensor; the suitable readings in the photodetectors are proportional to the overlap degree among the spectra of the sensor and filters. The calibration will be emphasized in simulations being compared with experimental results, and to recover mainly the deformed spectrum of Bragg Grating sensor for a suitable spectrum that will give the correct information at the position of sensor. The simulation ends in a recovery of the deformed spectrum, reducing measurement uncertainties and of the position of sensor, being compared with experimental results.
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Chwang, Jerry J. S. "Evaluation of fiber optic Bragg grating sensors in monitoring the integrity of structures repaired with bonded patches." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0018/MQ45572.pdf.
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NUNES, LUIZ CARLOS DA SILVA. "ANALYSIS OF THE DEMODULATION TECHNIQUE BASED ON FIXED FILTERS IN THE INTERROGATION OF FIBER BRAGG GRATING SENSORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5385@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORDEUTSCHER AKADEMISCHER AUSTAUSCHDIENST
A análise da técnica de demodulação usada para interrogar sensores a rede de Bragg em fibras ópticas baseadas em filtros fixos foi realizada teoricamente e experimentalmente. Diferentes configurações de sistemas foram analisadas modificando a posição espectral dos filtros, assim como os níveis de potência óptica obtidos nos fotodetectores. Foram realizadas medidas com o tempo de integração que variavam de 0.01 a 1s e estimado o limite de baixa freqüência. Comparação entre os resultados experimentais e simulados mostram boa concordância, e extrapolações indicam que seria possível chegar a uma faixa de medida da ordem de 7 nanômetros, com incertezas equivalentes menores que 2 picometros, na medida da posição de pico do sensor. Foi feita uma análise da possibilidade de utilização desta técnica para medida simultânea de pressão e temperatura com uma única rede sensora. Na realização experimental foi usado um transdutor de pressão que transferia uma força transversal à fibra, proporcional à pressão atuante, gerando birrefringência na região da rede de Bragg. Foi possível obter valores de pressão com a faixa dinâmica de 400 psi com incerteza máxima de 4 psi e simultaneamente temperaturas com variação de 28 a 50 graus Celsius com incerteza máxima de 0.1 graus Celsius. Adicionalmente, foram estudados os efeitos gerados em uma multiplexação temporal (TDM) de sensores a rede de Bragg quando os sensores se encontram superpostos na mesma posição espectral. Nesta análise é confrontada a técnica de demodulação utilizando dois filtros fixos com a técnica baseada na posição espectral. Os resultados indicam que a técnica baseada em filtros fixos apresenta vantagem, permitindo um número significativamente maior de sensores. E também, foi analisado o distúrbio provocado no espectro da rede sensora quando a fonte de luz usada para interrogar a rede tem uma modulação espectral que varia com a temperatura. Finalmente, foi apresentado um sistema de multiplexação (TDM/WDM), completamente polarizado, capaz de interrogar dezenas de sensores a rede de Bragg escrito em fibras de alta birrefringência. O sistema de multiplexação consistiu em uma chave óptica integrada, baseada em um interferômetro de Mach-Zehnder com configuração X-Y, e em um espectrômetro com um CCD linear como elemento de detecção.
The analysis of a demodulation system for fiber Bragg grating sensors based on two fixed spectral filters has been carried out both theoretically and experimentally. Different system configurations were analyzed by modifying the spectral position of the filters as well as the optical power-level of the signal reaching the two photo-detectors. Measurements with integration times that varied from 0.01 to 1 second have been compared with the low frequency limit predicted for long-term operation. Comparisons between simulated and experimental results show good agreement, and extrapolations indicate that it should be possible to achieve a dynamic range of the order of 7 nanometers, with uncertainties equivalent to less than 2 picometers, in measurements of the sensor peak position. Applications based on this system were carried out. An analysis of simultaneous measurement of temperature and pressure with only one FBG sensor using transducer of pressure to transfer a lateral force to the fiber, proportional to the applied pressure, generating birefringence at grating Bragg region has been realized. The proposed system allowed to measure pressure range of 400 psi with uncertain of 4 psi and simultaneously temperature range of 22 Celsius Degree with uncertain of 0.1 Celsius Degree. In addiction, generated effects in the temporal multiplexing (TDM) of fiber Bragg grating sensors when the sensor spectra are fully overlapped have been analyzed. In this study, it is compared the demodulation technique based on two fixed filters with the conventional technique based on the peak position. The results show that the technique based on fixed filters presents advantage to conventional, allowing a greatest sensor number. It was also analyzed the generated disturbance in the Bragg grating sensor spectrum when the source used to interrogate the sensor has a residual modulation which changes with the temperature. And finally, a polarized multiplexing system (TDM/WDM) able to interrogate a large number of Bragg grating sensors written in high-birefringent polarization-maintaining fibers has been realized. It is based on integrated-optic switch Mach- Zehnder interferometer in X-Y configuration and a CCD line array spectrometer.
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QUINTERO, SULLY MILENA MEJIA. "APPLICATIONS OF FIBER BRAGG GRATING SENSORS IN THE MEASUREMENT OF PH AND OF STRAIN IN HARD THIN FILMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9243@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho versa sobre duas diferentes aplicações de sensores a redes de Bragg em fibra óptica. A primeira consiste no desenvolvimento de uma técnica de sensoriamento do pH empregando fibra óptica, que visa a monitoração contínua e permanente deste parâmetro em poços de petróleo depletados e de injeção. Nesta aplicação, as redes de Bragg são acopladas, através de um mecanismo transdutor, a sistemas poliméricos que respondem a alterações do pH apresentando uma variação expressiva de seu volume. O tempo de resposta e o fator de inchamento do sistema polimérico foram caracterizados para valores de pH 3, 4, 5, e 6, em soluções aquosas contendo sais dissolvidos em concentrações típicas das encontradas em águas de formação. As medições foram realizadas a temperaturas e pressões ambientes, assim como na presença de óleo, e após a pressurização do sistema polimérico até 5000 psi. Diferentes mecanismos transdutores foram projetados e construídos, e suas respostas, avaliadas em soluções aquosas com composição similar à das águas de formação. Foram estimadas a sensibilidade da técnica e as principais fontes de incerteza na medição do pH. Procurou-se também avaliar a funcionalidade dos mecanismos transdutores visando uma futura instalação em poço. Na segunda aplicação, é proposta uma técnica para a medição in situ da tensão residual induzida em filmes finos de alta dureza durante sua deposição em câmaras de sputtering assitido por rádio-frequência e campo magnético. A técnica é constituída por uma viga em aço engastada, tendo uma de suas faces instrumentada com um conjunto de redes de Bragg a fibra óptica, enquanto a face oposta é exposta ao fluxo de íons do material a ser depositado. O sistema sensor é instalado em uma câmara que opera sob alto vácuo, enquanto os aparelhos de leitura permanecem no exterior. A resposta do protótipo em função de variações do campo magnético e da temperatura no interior da câmara foi levantada. Em seguinda, foram realizadas medições da deformação da viga durante a deposição de filmes de sílica, de óxido de titânio-índio, e de carbeto de silício. A tensão residual dos filmes foi calculada e comparada com resultados de medições de curvatura do substrato realizadas empregando um perfilômetro. Tensões residuais de 6 MPa até 0,2 Gpa foram obtidas durante as diferentes deposições.
This work treats of two different applications of optical fiber Bragg grating sensors. The first application consists of a pH sensing technique that employs optical fiber to permanent and continuously monitor the pH in depleted and injection oil wells. In this application, the Bragg gratings are coupled by a transduction mechanism to a polymeric system which responds to pH variations with a large volume change. The response time as well as the swelling factor of the polymeric system at pH 3, 4, 5, and 6 have been characterized in aqueous solutions with dissolved salts in concentrations typical of those found in formation waters. Experiments have been carried out at room temperature and pressures, in the presence of oil, and after pressurization up to 5000 psi. Several mechanisms of transduction have been designed, constructed, and tested in solutions similar to the formation waters. The sensitivity of the technique and the main sources of uncertainties related to the pH measurement have been investigated. Also, the functionality of the mechanisms has been evaluated aiming at a future installation in the petroleum wells. The second application investigated is a technique for in situ measurement of the residual stress induced in hard thin films during deposition by RF magnetron sputtering. The sensing technique consists of a cantilever steel beam. One of the surfaces of the beam is instrumented using optical fiber Bragg gratings; the opposite face is exposed to the ion flux that originates the thin film. The sensing system is installed in a vacuum chamber while the interrogating apparatus remains outside. The prototype has been characterized with respect to variations of the magnetic field and the temperature inside the chamber. Measurements of the beam strain have been carried out during deposition of silica, indium- titanium oxide, and silicon carbide thin films. The residual stresses have been calculated and the results compared with data obtained using perfilometry. Residual stress values varying from 6 MPa up to 200 MPa have been obtained during the different deposition processes.
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Lebid, Solomija [Verfasser], Christian [Gutachter] Schäffer, Jaroslaw [Gutachter] Bobitski, and Werner [Gutachter] Daum. "Perturbations in behaviour of fibre Bragg grating sensors introduced by local thermal and mechanical influences / Solomija Lebid ; Bundesanstalt für Materialforschung und -prüfung (BAM) ; Gutachter: Christian Schäffer, Jaroslaw Bobitski, Werner Daum." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2004. http://d-nb.info/1122836635/34.
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Bordonaro, Giancarlo Giuseppe. "Nonlinear System Identification of Physical Parameters for Damage Prognosis and Localization in Structures." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/30019.
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The understanding of how structural components endure loads, in particular variable loads, is that these components gradually, over some period of time depending on the nature of the loading and the material, develop a microcrack. After some additional time and loading, the microcrack grows to a size that might be detected. Beyond that point, the microcrack propagates in a manner that can be reliably predicted by computer analysis codes. Consequently, one can define different stages for the life of a structural component. These are: 1) the period prior to the formation of a microcrack, 2) the period of microcrack growth, and finally 3) the period of crack growth. To date, structural health monitoring approaches that seek to detect cracks offer no insight into the extent of deterioration occurring in the initial stage that is a precursor to the formation of the microcrack or its growth. However, an approach that would facilitate monitoring the extent of the deterioration that takes place during this stage promises to improve life prediction capabilities of structural components.
The challenge, thus, is to develop quantitative assessment of damage accumulation from the earliest stages of the fatigue process and to provide a structure's signature that is dependent of the damage stage. One such signature is the structure's response to forced excitation. The realization of such a goal would help in advancing structural health monitoring procedures using interrogative system identification techniques and determine sensitivities of physical parameters to damage. Additionally, vibration-based spectral quantities are related to physical properties of the structure under test.
In this thesis, nonlinear response to parametric excitation is exploited for nonlinear system identification of metallic and composite beam-mass systems before damage initiation through intermediate states of damage progression to failure. Parametric identification procedure combines linear and higher order spectral analysis of vibration measurements and perturbation techniques for the derivation of the approximate solution of the system nonlinear governing differential equation. The possibility of using optical Fiber Bragg Grating sensors technology for damage localization is also assessed. Spectral moments and quantities obtained from fiber optic strain measurements are evaluated near and away from cracks to assess the relation between these moments and cracks.
Variations in parameters representing natural frequency, damping and effective nonlinearities for different levels of progressive damage in a beam-mass system have been determined. Their percentage variations have been quantified to establish their sensitivities to damage initiation. The results show that damping and effective nonlinearity parameters are more sensitive to damage conditions than the natural frequency of the first mode. Crack localization is assessed by means of optical fiber technology for a composite beam-mass system. The results show that noise levels in fiber optic signals are high in comparison to strain gage signals. Of particular interest, however, is the observation that the nonlinear response is more pronounced near the cracks than away from them.Ph. D.
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Mahesh, Kondiparthi. "Novel Methods To Interrogate Fiber Bragg Grating Sensors." Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/1926.
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A novel detection technique to estimate the amount of chirp in fiber Bragg gratings (FBGs) is proposed. This method is based on the fact that reflectivity at central wavelength of FBG reflection changes with strain/temperature gradient (linear chirp) applied to the same. Transfer matrix approach was used to vary different grating parameters (length, strength and apodization) to optimize variation of reflectivity with linear chirp. Analysis is done for different sets of ‘FBG length-refractive index strength’ combinations for which reflectivity vary linearly with linear chirp over a decent measurement range. This work acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection.
A novel high sensitive FBG strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities
considering all major noise contributions are respectively of the order of 25 pε/ Hz and
1.2nε /
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Guru, Prasad A. S. "Fiber Bragg Grating Sensors : An Exploration Of Applications In Diverse Fields." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2507.
Full textAbstract:
Sensors have become essential elements in human life for safe and comfortable existence in the ever demanding world. Various technologies over decades have contributed in their own way fulfilling innumerable sensing requirements. The discovery of optical sensor technologies has revolutionized the sensing field due to their inherent advantages. Among the large number of fiber optic sensor technologies, FBG based sensors have become widely known and popular within and outside the photonics community and has seen a prominent rise in their utilization.
This thesis explores the use of FBG sensors for a wide range of applications scanning across a variety of engineering and medical applications, in the areas of civil engineering, biomechanical engineering, aerospace engineering, geoengineering, etc. It also deals with newer methods of packaging FBG sensors for the measurement of specific engineering parameters like strain, temperature, pressure, displacement and vibration.
In the field of civil engineering, FBG sensors are employed for strain sensing on a prism and furthermore tested on a full size brick wallet. During this study, emphasis is made on substituting traditional sensors by specially packaged FBG sensors with the intent of either enhancing the sensing system’s performance or in merging/uniting the inherent advantages of FBG sensors.
In the area of biomechanics, a novel sensor methodology using FBG sensors, for measuring surface strains generated on the skin of the calf muscle during various leg exercises is proposed. This methodology is used to address one of the most critical and life threatening issues in long distance air travel, namely the Deep Vein Thrombosis. Further, a FBG sensor based plantar sensing plate, is designed and developed, to measure plantar strain distribution in foot and also to analyze the postural stability.
In the field of aerospace engineering, FBG sensors are used for addressing two of the most vital issues; Structural Health Monitoring (SHM) and direct measurement of pressure and temperature on the surface of an aircraft under hypersonic wind flow. Carbon Fiber Composite coupon level testing is carried out to obtain a generic strain calibration factor for the FBG sensor. Further, FBG sensors are exploited for the direct measurement of absolute temperature and pressure on the leeward surface of blunt cone at hypersonic wind speeds.
In the domain of geoengineering, the feasibility studies have been undertaken to use a FBG as a seismic sensor and as a bore-well characterizing sensor. A novel FBG seismic sensor package is developed using a single FBG sensor to pick up the seismic waves propagating through the ground generated from earthquakes and ground tremors. Further, FBG sensors are used for measurement of temperature profiles in a bore-well to delineate and characterize the behavior of fractures during seasonal climatic changes. To summarize, the present thesis demonstrates a comprehensive experimental study which bring out the utility of FBG sensors in a variety of challenging applications.
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Zhan, Chun. "Femtosecond laser inscribed fiber Bragg grating sensors." 2007. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2298/index.html.
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Yamdagni, Sumeet. "Fiber Bragg Grating Interrogation Systems." Thesis, 2009. http://hdl.handle.net/2005/925.
Full textAbstract:
This thesis work deals with the development of three different categories of interrogation techniques for Fiber Bragg Grating based sensor networks. Such networks are used for structural health monitoring and other applications.
A bulk grating based interrogation system is described first, which includes an optical source, switch, circulator, embedded controller, and software. The center wavelength determination technique employed is detailed and is shown to be highly accurate from test data. The comparison with resistance strain gauges is presented which shows that the system developed provides an accurate strain reconstruction. The system is also compared with a commercial optical spectrum analyzer and is found to exhibit good accuracy and fidelity. The system has been field tested on an aircraft structure with 14 sensors spread over 4 channels. Strain data reconstruction from these tests is shown to accurately reproduce the loading conditions.
A second system developed is based on the matched filter technique using a mechanical fiber stretcher; the details of this system are presented with a mathematical treatment of the technique. The design of the fiber stretcher is also described. This design is regarded to be novel since it tries to provide large interrogation bandwidths using a parallel topology. The results of tests have shown good resolution and comparative tests with resistance strain gauges have shown accurate reproduction of strain.
Finally, an interrogation system based on a wavelength tunable source is presented. This system is a precursor to a time division multiplexed interrogation system, which has also been described. Three laser configurations have been set up and characterized. The laser sweep tests have been performed on two configurations and a sensor grating reconstruction test has also been carried out.
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Dennison, Christopher Raymond Stuart. "Development and application of in-fibre Bragg grating based biomedical pressure sensors." Thesis, 2008. http://hdl.handle.net/1828/1025.
Full textAbstract:
Two in-fibre Bragg grating based optical pressure sensors were developed to
address the limitations of conventional solid-state electronic biomedical sensors. The first
sensor, developed for intervertebral disc pressure measurements varying over several
MPa, had a major diameter of only 400 μm and sensing area of 0.03 mm2. This sensor
was validated in spine biomechanics studies and was shown to: give accurate and
repeatable measurements, be compatible with the small (e.g. cervical) discs, and alter disc
mechanics less than the current alternative sensor. This sensor is also the smallest, most
mechanically compliant disc pressure sensor presented to date.
The second FBG sensor was developed to measure sub-kPa pressure variations
and had a major diameter and sensing area of only 200 μm and 0.02 mm2, respectively.
This sensor achieves sub-kPa repeatability through a novel design that is approximately
100 times smaller than other FBG sensors presented with sub-kPa pressure repeatability.
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Yang, Chao-hsiang, and 楊兆祥. "Fiber Sensors Based on Long Period Grating Series with Fiber Bragg Grating." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/02903471872113234178.
Full textAbstract:
碩士逢甲大學
電機工程所
98
The content of this thesis is to investigate a new fiber sensor for simultaneously measuring the pressure and temperature with a packaged fiber Bragg grating (FBG) connected in a series with a long-period fiber grating (LPG). The central wavelength of an FBG is fabricated on the negative slope region of the loss peak of LPG transmission spectrum and the FBG is encapsulated in a polymer-half-filled metal cylinder with two openings on opposite sides of the wall of the polymer to measure the pressure. Utilizing the different optical response of the FBG and LPG, the applied pressure and temperature will cause the variation of the center-wavelength and reflection of an FBG simultaneously. Therefore, the sensor can be used to measure pressure and temperature simultaneously. For this fiber grating sensor without packaging, the stress sensitivities both of 0.013nm/gw and 0.039dB/gw are experimentally obtained. The temperature sensitivities both of 0.0096nm/OC and 0.124dB/OC are experimentally identified. After the sensor has been packaged, the temperature sensitivities become 0.02nm/OC and 0.39 dB/OC and the pressure sensitivities are greatly improved with the value of 7.5nm/bar and 7.76dB/bar. This sensor can be applied in the water-level measurement under different temperatures with the wavelength-shift sensitivities of 0.017 nm/cm and 0.021nm/ OC as well as the sensitivities of reflection intensity of -0.013 dB/cm and 0.56 dB/ OC.
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Roberson, Craig Valentine. "An investigation into performance criteria for Fibre Bragg Grating sensors embedded in composite structures." Thesis, 2014. http://hdl.handle.net/10210/12124.
Full textAbstract:
M.Ing. (Mechanical Engineering)The dissertation explores the applications and limitations of optic Fibre Bragg Grating (FBG) sensors for the purpose of structural health monitoring of high performance composite aerospace structures. The absence of a set of stringent performance criteria governing the form and function of a sensory system for embedded high performance applications highlights the major hurdle to be overcome before widespread acceptance of these technologies becomes apparent. The dissertation therefore develops through an extensive literature study a basic framework of performance criteria to be met by the sensory system upon which a prototype Structural Health Monitoring (SHM) system can be further developed. The resolution of the performance criteria into categories of mechanical and non-mechanical performance allows independent evaluation of factors that directly affect the performance of the sensor (in terms of strength, embeddability and load carrying ability) as well as its functional performance (in terms of orientation, spatial resolution and measurement philosophy). The literature study uses the non-mechanical performance limitations as a guideline for the selection of Fibre Bragg Grating (FBG) sensors as the sensory mechanism. The mechanical performance limitations of these specific sensors are then called into question and evaluated. Independent experiment campaigns are therefore developed to evaluate the mechanical and non-mechanical performance limitations such that a set of performance criteria can be developed governing the use of embedded sensory systems. Non mechanical performance with particular emphasis on sensor placement and orientation is investigated by simulating a fixed-free Euler Bernoulli cantilever using the Finite Element Method (FEM). The ability of the sensor to identify structural changes by measuring changes in modal response shows good results. Furthermore the inability of modal based monitoring to identify structural changes in the vicinity of modal inflection points is identified as an opportunity to locate structural deficiencies by monitoring multiple modes with known inflection point positions. The method also provides recommendations of sensor placement and orientation (close to the beam fixture and parallel with the neutral axis) such that the effectiveness of strain component measurements from all measurable modes is maximised. Mechanical performance of embedded FBG sensors is evaluated through an extensive fracture testing program which measures the fracture strains of fibre samples subjected to two-point bending. The fracture test program allows the quantification of the effects of the presence of the fibre’s protective polymer coating on fibre embeddability in composites, the consequent effects that the removal of this coating has on the mechanical performance and fracture behaviour of FBG sensors. These effects are qualified and mitigatory measures developed to improve the mechanical performance. A system of crack masking, hydrofluoric acid etching and fibre treatment is developed and statistical data analysis methods are employed and refined such that improvements in the mechanical properties of the FBG sensors can be quantified. An evaluation of the effectiveness of the proposed mechanical performance improvements yields good results culminating in the development of a comprehensive set of mechanical performance criteria to facilitate further development of a reliable SHM system.
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Fan, Chen-Chi, and 范振琦. "Array Type of Fiber Bragg Grating Strain Sensors." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/51338812607455297758.
Full textAbstract:
碩士正修科技大學
電子工程研究所
95
The traditional sensor usually used a strainometer, capacitance, inductance, piezoelectric materials, and so on to be the modulation mechanism or the sensing element. In substance, this method always involves the measure of voltages or the galvanometry, so it is easy to be interfered with electromagnetism and the magnetic field, but the fibre-optic sensor is not. The fibre-optic sensor still can be used after irradiation treated Ionizing Radiation, so it applys to strict circumstances. For example, a nuclear power plant. This thesis utilizes Fiber Bragg Grating(FBG) in order to detect the component mainly, utilize two kinds of main structure of the shape cost page thesis of the EDFA, in two kinds of main structure, the FBG comes by way of connecting in parallel and contacting separately to detect the changes of temperature and strain. While using more than two FBG in order to detect the component at the same time, because the ASE energy that the grating of the wavelength of longer centre pours into will be higher than the FBG smaller in wavelength of centre, inject with attenuator into centre wavelength heavy ASE energy of FBG decay 10%~15% can use two kinds of different in the center FBG of wavelengths among experiment. Detect the respect in the strain, learn in the experiment, under 9.8 Newton strain function, FBG centre wavelength is probably rectangular to translation 13.4nm to the long wave; detect the respect in temperature, the wavelength of centre, for FBG of 1540nm in order to detect the component, temperature rises from 10 from 1539.455 nm translation to 1540.6 nm to wavelength of centre 90 . The analysis and experiment of these principles and experiments with detailed structure prove, FBG can reach more steady, more accurate result of detecting.
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Chen, Chien-Cheng, and 陳建成. "The Design of Fiber Bragg Grating Vibration Sensors." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/58342265885099339027.
Full textAbstract:
碩士國立中山大學
電機工程學系研究所
91
The reflection wavelength of Fiber Bragg Grating is sensitive to the strain and the temperature’s variation. We use Fiber Bragg Grating to be the sensor head and measure the vibration frequency in constant temperature environment. The vibration of object can make the sinusoidal strain to Fiber Bragg Grating, and it will make a little phase difference to the light of the fiber. Using the interferometer and demodulation system, we can measure the phase difference and vibration frequency. Our sensor configuration is made up of imbalance Mach-Zehnder interferometer and Fiber Bragg Grating. The two light of different path need different time to pass through the vibration source, so they make phase difference. We use the demodulation circuit to measure the phase difference causing by vibration and get the vibration frequency. Our experiment structure is a novel configuration of Fiber Bragg Grating vibration sensor. Its intensity of signal is larger than the intensity of original sensor configuration, about 4dB.The novel sensor configuration is easier spread than traditional accelerometer and it is designed of all fiber. The accuracy for measuring low frequency vibration is 99.971%. The Dynamic range of the system is more than 45dB. It is larger than the dynamic range of original sensor configuration, about 9dB. The smallest signal that can be measured is about 0.0075rad.
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"Evaluation of optical fibre Bragg grating sensors on a sidewall wind tunnel balance." Thesis, 2015. http://hdl.handle.net/10210/13810.
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