Dissertations / Theses on the topic 'Fibre Optic Sensing'
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1
Attridge, John Worthington. "Fibre optic chemical sensing." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37931.
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Khaliq, Sarfraz. "Fibre-optic long period gratings for sensing applications." Thesis, Cranfield University, 2003. http://dspace.lib.cranfield.ac.uk/handle/1826/7886.
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Long period gratings (LPGs) are formed by inducing a permanent periodic modulation of the refractive index (RI) of the core of an optical fibre. The transmission spectrum of the LPG contains a series of attenuation bands centered at discrete wavelengths. The exact form of the transmission spectrum and the central wavelengths of the attenuation bands, are sensitive to the period and the length of the LPG and to the local environment. The sensitivity of a LPG to a particular measurand is dependant upon the composition of the fibre and upon the order of the cladding mode to which the guided mode is coupled to and is thus different for each attenuation band. Cont/d.
3
Bownass, David Casson. "Passive fibre-optic humidity sensing for telecommunications networks." Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/1191.
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4
Flannery, D. "Fibre optic chemical sensing using Langmuir-Blodgett overlay waveguides." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/10719.
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Fibre
optic chemical sensing has been demonstrated using side-polished single mode
optical bre, evanescently coupled to chemically sensitive Langmuir-Blodgett overlay
waveguides. The sensors exhibit a channel dropping response centred on a wavelength
dependent upon the thickness and refractive index of the overlay waveguide. It has been
shown that
chemically sensitive organic dyes prove to be suitable materials for forming
the
overlay waveguide whereas the Langmuir-Blodgett deposition technique provides the
required overlay thickness control.
A brief
optic pH sensor has been demonstrated by
depositing a merocyanine dye onto a
side-polished optical fibre which exhibits a change in transmission of 9.7 ± 0.8 dB pH" at
a
working wavelength of 750 n and 4.2 ± 0.5 dB pH`1 at 780 nm, with a shift in the
channel
dropping centre wavelength of 18.8 ± 0.8 n pH`1. The response time of the
sensor to a
step change in pH has been measured to be ~ 20 s.
The
advantage of being able to chemically engineer the organic materials used to form
the
overlay waveguides has been demonstrated by manufacturing a second pH sensor
designed to operate at longer wavelengths using a second, modified merocyanine dye.
The overall
wavelength response of this second sensor to pH has been shown to be non-
linear but a
sensitivity of 23.3 ± 0.3 n pH`l is observed over a linear region. Finally, i
order to
investigate the non-linear response, a computer model based on the Kramers-
Kronig relations has been devised and shows good agreement with experimental values.
l
5
Flannery, Damian. "Fibre optic chemical sensing using Langmuir-Blodgett overlay waveguides." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/10719.
Full textAbstract:
Fibre optic chemical sensing has been demonstrated using side-polished single mode optical bre, evanescently coupled to chemically sensitive Langmuir-Blodgett overlay waveguides. The sensors exhibit a channel dropping response centred on a wavelength dependent upon the thickness and refractive index of the overlay waveguide. It has been shown that chemically sensitive organic dyes prove to be suitable materials for forming the overlay waveguide whereas the Langmuir-Blodgett deposition technique provides the required overlay thickness control. A brief optic pH sensor has been demonstrated by depositing a merocyanine dye onto a side-polished optical fibre which exhibits a change in transmission of 9.7 ± 0.8 dB pH" at a working wavelength of 750 n and 4.2 ± 0.5 dB pH`1 at 780 nm, with a shift in the channel dropping centre wavelength of 18.8 ± 0.8 n pH`1. The response time of the sensor to a step change in pH has been measured to be ~ 20 s. The advantage of being able to chemically engineer the organic materials used to form the overlay waveguides has been demonstrated by manufacturing a second pH sensor designed to operate at longer wavelengths using a second, modified merocyanine dye. The overall wavelength response of this second sensor to pH has been shown to be non- linear but a sensitivity of 23.3 ± 0.3 n pH`l is observed over a linear region. Finally, i order to investigate the non-linear response, a computer model based on the Kramers- Kronig relations has been devised and shows good agreement with experimental values.
6
de, Souza Keith R. C. P. "Fibre-optic distributed sensing based on spontaneous Brillouin scattering." Thesis, University of Southampton, 1999. https://eprints.soton.ac.uk/351507/.
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This thesis reports on the use of spontaneous Brillouin scattering for the purpose of fibre-optic distributed temperature and strain sensing based on a time-domain Landau-Placzek ratio technique. Detection system specifications are dictated by the spatial resolution, range, measurand resolution and measurement time. Pulsed sources are used in these sensors. The minimum spatial resolution depends on both the pulse width and receiver bandwidth. The range and measurand resolution depend on the peak pulse power launched into the sensing fibre as well as the Brillouin signal-to-noise characteristics at the receiver. The maximum launched pulse power is limited by the onset of nonlinear effects in the sensing fibre. Novel interferometric techniques based on low-cost, low loss all fibre Mach-Zehnder interferometric optical filters needed to separate the backscattered Rayleigh and spontaneous Brillouin signals have been developed with enhanced signal-to-noise capabilities. Used in conjunction with a newly developed low noise optical preamplifier /transimpedance receiver system, a distributed temperature sensor having 1.8m spatial resolution, 6.3 °C temperature resolution and a range of 23km is demonstrated. The strain dependence of the spontaneous Brillouin intensity has been determined. This coefficient is crucial for the development of a distributed temperature only sensor and /or a combined distributed temperature and strain sensor. Pulsed narrowband and broadband sources are necessary for resolving the Rayleigh and Brillouin signals as well as reducing coherent Rayleigh noise. The latter has been investigated and its dependence on certain parameters confirmed. A source capable of switching between narrowband and broadband operation has been demonstrated and is particularly appropriate for extended periods of data collection cycles.
7
McMurtry, Stefan. "Multipoint humidity sensing based upon a multiplexed fibre optic sensor." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310209.
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Wait, Peter Collinson. "The application of Brillouin scattering to distributed fibre optic sensing." Thesis, University of Southampton, 1997. https://eprints.soton.ac.uk/394568/.
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This thesis reports on an investigation into the application of Brillouin scattering for the purpose of distributed fibre optic sensing. The main focus of the work has been centred on a Brillouin optical time domain reflectometer (BOTDR) system. The behaviour of short (3m), medium (60m) and long (6km) erbium doped fibre amplifiers using narrow bandwidth pulsed signals has been investigated and the most suitable configuration for the source requirement of the BOTDR identified. The operation of a (BOTDR) system has been demonstrated at the low loss window of 1.5µm wavelength. Multiple Stokes orders of stimulated Brillouin scattering in a medium length erbium doped fibre amplifier using pulsed excitation are reported. The observed stimulated Brillouin threshold power is significantly reduced as a result of optical gain. The points of origin within the fibre of the generated Stokes pulses are located using space-time diagrams and are observed to depend on the Brillouin and Erbium pump powers. This has therefore been identified as a possible mechanism for sensing applications utilizing the novel technique of varying the pump powers to spatially interrogate the fibre. Measurements of the Brillouin scattering coherence length in silica fibre using a fibre Mach Zehnder interferometer are presented. As the Brillouin pump power is increased from below to above stimulated threshold, the line shape narrows and changes from that of a Lorentzian to a Gaussian. It is also shown that the Brillouin bandwidth approaches a limiting value. It is shown experimentally that the ratio of the intensities of Rayleigh and Brillouin backscattered light (Landau Placzek ratio) in an optical fibre has a temperature dependence which may be used for the basis of a distributed temperature sensor. This result, combined with the known frequency dependence of the Brillouin backscattering on temperature and strain, indicates spontaneous Brillouin backscatter may be used for the unique determination of either temperature or strain in a distributed fibre optic sensing system. Because of the coherent nature of Rayleigh scattering, use of the same narrow bandwidth source as required for the Brillouin signal in the Landau Placzek ratio method, results in significant coherent noise in the Rayleigh signal. A novel technique is demonstrated whereby the amplified spontaneous emission noise and amplifying properties of an erbium doped fibre amplifier may be exploited to reduce the coherent noise on the Rayleigh backscatter signal. This results in a significant improvement in both temperature and spatial resolution.
9
Wong, Rebecca. "Advanced fibre optic long period grating sensors : design, fabrication and sensing." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9153.
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This thesis describes the process and technique used to fabricate reproducible optical
fibre long period gratings (LPG) of various types. It explores how they can be
exploited for use as highly selective and sensitive sensors. A versatile method for
fabricating LPG sensors has been demonstrated. The single system has the capability
of fabricating LPGs of different configurations, such as uniform period, those
operating at the phase matching turning point (PMTP), as well as phase shifted
and chirped. LPGs were characterised for their sensitivities to temperature, axial
strain and surrounding refractive index. The gratings at the PMTP were found to
show higher sensitivities to external influences.
Novel sensing configurations that exploit the properties of LPGs were also constructed.
An LPG coated with a molecularly imprinted ceramic coating was demonstrated
to offer a selective method for porphyrin detection. A composite nanoscale
of a titanium oxide (TiO2) matrix and 5, 10, 15, 20 Tetrakis-(N-methyl-piridinium4-
yl)-21H, 23H-porphine tertakis (p-toluenesulfonate) [TMPyP] porphyrin template
film was deposited on the LPG via liquid phase deposition. Attempts to rebind porphyrins
to the matrix were carried out. The LPGs transmission spectrum exhibited
a higher sensitivity to the target TMPyP template than it did to other, structurally
similar porphyrins, showing high selectivity.
A continuously chirped long period grating (CCLPG) sensor for monitoring directional
flow and cure of an epoxy resin is also presented. The asymmetric properties
of the CCLPG were exploited to facilitate the measurement of the direction of the
flow. The CCLPG was also used to monitor changes in the refractive index of the
resin during its cure, showing close agreement with a fibre optic Fresnel refractometer.
10
Guillemain, Henri. "Fibre optic sensing techniques for the detection of lead (II) ions." Thesis, City University London, 2009. http://openaccess.city.ac.uk/12440/.
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Lead is an element with harmful effects to man and whose uses are being increasingly subject to legislations. This thesis describes the incorporation of two lead-sensitive reagents in different fibre optic sensing configurations. The reagents were carefully selected for their response towards lead. A probe was built for each reagent and a sensor system designed, constructed and tested with each probe followed by analysis of the experimental data obtained from them. The first reagent is a chromogenic dye whose absorption spectrum changes in the presence of lead ions. In this work, a reflectance-based probe is built and tested to exploit this feature. A robust referencing technique based on the performance of the probe is developed that allows the sensor to operate amid unstable conditions. The second reagent is a fluorophore whose fluorescence mechanism and affinity to lead ions are explained in detail. Based on its binding properties with lead, the sol-gel matrix is selected to encapsulate this reagent and a probe is thus constructed but in subsequent tests, no response to lead ion is detected. A hypothesis is put forward to explain the lack of reaction between lead and the fluorophore in its entrapped environment. As a result, the fluorophore is then utilised in solution where its characteristics have already been established and a capillary probe which exploits the capillary effect for its operation is constructed and evaluated. Existing analytical techniques are reviewed in this work and compared to fibre optic sensors whose various sensing configurations are then described. The instrumentation and measurement techniques used throughout this work are also discussed.
11
Chowdhury, S. A. "Fibre optic hydrogen sensing for long term use in explosive environments." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9874.
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Hydrogen is an explosive and flammable gas with a lower explosive limit of just 4% volume in air. It
is important to monitor the concentration of hydrogen in a potentially hazardous environment where
hydrogen may be released as a by-product in a reaction or used as a principal gas/liquid.
A fibre optic based hydrogen sensor offers an intrinsically safe method of monitoring hydrogen
concentration. Previous research studies have demonstrated a variety of fibre optic based techniques
for hydrogen detection. However the long-term stability of the hydrogen sensor and interrogation
system has not yet been assessed and is the focus of this study. In the case of sensor heads being
permanently installed in-situ, they cannot be removed for regular replacement, making long-term
stability and reliability of results an important feature of the hydrogen sensor.
This thesis describes the investigation and characterisation of palladium coated fibre optic sensor
heads using two designs of self-referenced refractometer systems with the aim of finding a system that
is stable in the long term (~6 months). Palladium was the chosen sensing material owing to its
selective affinity for absorbing hydrogen. Upon hydrogen absorption, palladium forms a palladium-
hydride compound that has a lower refractive index and lower reflectivity than pure palladium. The
refractometers measured the changes in the reflectivity to enable calculation of the concentration of
hydrogen present. A low detection limit of 10ppm H2 in air was demonstrated, with a response time of
40s for 1000ppm H2 in air.
A further aspect to sensor stability was investigated in the form of sensor heads that had a larger area
for palladium coverage. Hydrogen induced cracking in palladium is a common failure mechanism. A
hypothesis is presented that a larger sensor area can reduce the probability of catastrophic failure
resulting from cracks, which may improve the predictability of the sensor’s performance. Two sensor
head designs have been proposed – fibre with a ball lens at the tip and fibre with a GRIN lens at the
tip, both of which potentially offer a larger area than the core of a singlemode optical fibre. The limit
of detection and response times of the sensor heads were characterised in hydrogen. For long term
stability assessment of the sensor head and the interrogation unit, the system was left running for a
period of 1 to 4 weeks and the noise and drift in the system was quantified using an Allan deviation
plot.
12
Niewczas, Pawel. "Implementation of a Faraday Effect based optical current transducer using digital signal processing techniques." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248515.
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Choi, Ming Fat. "Investigations into fibre optic sensing systems for gaseous oxygen and carbon dioxide." Thesis, University of the West of England, Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240829.
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Mei, Ying. "Error analysis for distributed fibre optic sensing technology based on Brillouin scattering." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/278660.
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This dissertation describes the work conducted on error analysis for Brillouin Optical Time Domain Reflectometry (BOTDR), a distributed strain sensing technology used for monitoring the structural performance of infrastructures. Although BOTDR has been recently applied to many infrastructure monitoring applications, its measurement error has not yet been thoroughly investigated. The challenge to accurately monitor structures using BOTDR sensors lies in the fact that the measurement error is dependent on the noise and the spatial resolution of the sensor as well as the non-uniformity of the monitored infrastructure strain conditions. To improve the reliability of this technology, measurement errors (including precision error and systematic error) need to be carefully investigated through fundamental analysis, lab testing, numerical modelling, and real site monitoring verification. The relationship between measurement error and sensor characteristics is firstly studied experimentally and theoretically. In the lab, different types of sensing cables are compared with regard to their measurement errors. Influences of factors including fibre diameters, polarization and cable jacket on measurement error are characterized. Based on experimental characterization results, an optics model is constructed to simulate the Brillouin back scattering process. The basic principle behind this model is the convolution between the injected pulse and the intrinsic Brillouin spectrum. Using this model, parametric studies are conducted to theoretically investigate the impacts of noise, frequency step and spectrum bandwidth on final strain measurement error. The measurement precision and systematic error are then investigated numerically and experimentally. Measurement results of field sites with installed optical fibres displayed that a more complicated strain profile leads to a larger measurement error. Through extensive experimental and numerical verifications using a Brillouin Optical Time Domain Reflectometry (BOTDR), the dependence of precision error and systematic error on input strain were then characterized in the laboratory and the results indicated that a) the measurement precision error can be predicted using analyzer frequency resolution and the location determination error and b) the characteristics of the measurement systematic error can be described using the error to strain gradient curve. This is significant because for current data interpretation process, data quality is supposed to be constant along the fibre although the monitored strain for most of the site cases is non-uniformly distributed, which is verified in this thesis leading to a varying data quality. A novel data quality quantification method is therefore proposed as a function of the measured strain shape. Although BOTDR has been extensively applied in infrastructure monitoring in the past decade, their data interpretation has been proven to be nontrivial, due to the nature of field monitoring. Based on the measurement precision and systematic error characterization results, a novel data interpretation methodology is constructed using the regularization decomposing method, taking advantages of the measured data quality. Experimental results indicate that this algorithm can be applied to various strain shapes and levels, and the accuracy of the reconstructed strain can be greatly improved. The developed algorithm is finally applied to real site applications where BOTDR sensing cables were implemented in two load bearing piles to monitor the construction loading and ground heaving processes.
15
Wang, Haichao. "A fibre optic system for distributed temperature sensing based on raman scattering." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5498.
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This thesis is based on a research project to monitor the temperature profile along a power cable using the fibre optic Distributed Temperature Sensing (DTS) technology. Based on the temperature measured by a DTS system, real time condition monitoring of power cables can be achieved.
In this thesis, there are three main research themes.
1. Develop a DTS system for industrial applications. The entire hardware system and measuring software are developed to be an industrial product. Multiple functions are provided for the convenience of users to conduct temperature monitoring, temperature history logging and off-line simulation.
2. Enhance the robustness of the DTS system. An algorithm for signal compensation is developed to eliminate the signal fluctuation due to disturbance from the hardware and its working environment. It ensures robustness of the system in industrial environments and applicability to different system configurations.
3. Improve the accuracy of the DTS system. A calibration algorithm based on cubic spline fitting is developed to cope with non-uniform fibre loss in the system, which greatly improved the accuracy of the temperature decoding in real applications with unavoidable nonlinear
characteristics.
The developed DTS system and the algorithms have been verified by continuous experiments for about one year and achieved a temperature resolution of 0.1 degree Celsius, a spatial resolution of 1 meter, and a maximum error of 2 degree Celsius in an optic fibre with the length of 2910 metres.
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Jason, Johan. "Fibre-Optic Displacement and Temperature Sensing Using Coupling Based Intensity Modulation and Polarisation Modulation Techniques." Doctoral thesis, Mittuniversitetet, Avdelningen för elektronikkonstruktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-18964.
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Optical fibre sensors are employed in the measurements of a number of different physical properties or for event detection in safety and security systems. In those environments which suffer from electromagnetic disturbance, in harsh environments where electronics cannot survive and in applications in favour of distributed detection, fibre-optic sensors have found natural areas of use. In some cases they have replaced conventional electronic sensors due to better performance and long-term reliability, but in others they have had less success mainly due to the higher costs which are often involved in fibre-optic sensor systems. Intensity modulated fibre-optic sensors normally require only low-cost monitoring systems principally based on light emitting diodes and photodiodes. The sensor principle itself is very elemental when based on coupling between fibres, and coupling based intensity modulated sensors have been utilised over a long period of time, mainly within displacement and vibration sensing. For distributed sensing based on intensity modulation, optical time domain reflectometer (OTDR) systems with customised sensor cables have been used in the detection of heat, water leakage and hydrocarbon fluid spills. In this thesis, new concepts for intensity modulated fibre-optic sensors based on coupling between fibres are presented, analysed, simulated and experimentally verified. From a low-cost and standard component perspective, alternative designs are proposed and analysed using modulation function simulations and measurements, in order to find an improved performance. Further, the development and installation of a temperature sensor system for industrial process monitoring is presented, involving aspects with regards to design, calibration, multiplexing and fibre network installation. The OTDR is applied as an efficient technique for multiplexing several coupling based sensors, and sensor network installation with blown fibre in microducts is proposed as a flexible and cost-efficient alternative to traditional cabling. As a solution to alignment issues in coupling based sensors, a new displacement sensor configuration based on a fibre to a multicore fibre coupling and an image sensor readout system is proposed. With this concept a high-performance sensor setup with relaxed alignment demands and a large measurement range is realised. The sensor system performance is analysed theoretically with complete system simulations, and an experimental setup is made based on standard fibre and image acquisition components. Simulations of possible error contributions show that the experimental performance limitation is mainly related to differences between the modelled and the real coupled power distribution. An improved power model is suggested and evaluated experimentally, showing that the experimental performance can be improved down towards the theoretical limit of 1 μm. The potential of using filled side-hole fibres and polarisation analysis for point and distributed detection of temperature limits is investigated as a complement to existing fibre-optic heat detection systems. The behaviour and change in birefringence at the liquid/solid phase transition temperature for the filler substance is shown and experimentally determined for side-hole fibres filled with water solutions and a metal alloy, and the results are supported by simulations. A point sensor for on/off temperature detection based on this principle is suggested. Further the principles of distributed detection by measurements of the change in beat length are demonstrated using polarisation OTDR (POTDR) techniques. It is shown that high-resolution techniques are required for the fibres studied, and side-hole fibres designed with lower birefringence are suggested for future studies in relation to the distributed application.Fiberoptiska sensorer används för mätning av ett antal olika fysikaliska parametrar eller för händelsedetektering i larm- och säkerhetssystem. I miljöer med elektromagnetiska störningar, i andra besvärliga miljöer där elektronik inte fungerar samt i tillämpningar där distribuerade sensorer är att föredra, har fiberoptiska lösningar funnit naturliga applikationer. I vissa fall har de ersatt konventionella elektroniska sensorer på grund av bättre prestanda och tillförlitlighet, medan de i andra sammanhang har haft mindre framgång huvudsakligen på grund av den i många fall högre kostnaden för fiberoptiska sensorsystem. Intensitetsmodulerade fiberoptiska sensorer kräver normalt endast billiga utläsningssystem huvudsakligen baserade på lysdioder och fotodioder. Principen för sådana sensorer baserade på koppling mellan fibrer är mycket enkel, och denna typ av sensorer har haft tillämpningar under en lång tid, främst inom mätning av positionsförändring och vibrationer. För distribuerade intensitetsmodulerade sensorer har system baserade på optisk tidsdomän-reflektometer (OTDR) och skräddarsydda sensorkablar funnit tillämpningar i detektion av värme/brand, vattenläckage och kolvätebaserade vätskor. I denna avhandling presenteras, simuleras, testas och utvärderas praktiskt några nya koncept för kopplingsbaserade intensitetsmodulerade fiberoptiska sensorer. Från ett lågkostnads- och standardkomponentperspektiv föreslås och analyseras alternativa lösningar för förbättrad prestanda. Utveckling och installation av en temperatursensor för en industriell tillämpning, innehållande aspekter på sensormultiplexering och nätverksbyggande, behandlas. OTDR-teknik används som en effektiv metod för multiplexering av flera kopplingsbaserade sensorer, och installation av sensornätverk genom användning av blåsfiberteknik och mikrodukter föreslås som ett flexibelt och kostnadseffektivt alternativ till traditionell kabelinstallation. Som en lösning på förekommande upplinjeringsproblem för kopplingsbaserade sensorer, föreslås en ny sensorkonfiguration baserad på koppling mellan en fiber och en multikärnefiber/fiberarray och med ett bildsensorsystem för detektering. Med detta koncept kan ett högpresterande, upplinjeringsfritt sensorsystem med ett stort mätområde åstadkommas. Sensorsystemets prestanda har analyserats teoretiskt med kompletta systemsimuleringar, och en experimentell uppställning baserad på standardfiber och en kamera av standardtyp har gjorts. Simuleringar av möjliga felbidrag visar att systemets experimentella prestanda främst begränsas av skillnader mellan den modellerade och den verkliga optiska effektfördelningen. En förbättrad modell för effektfördelningen föreslås och utvärderas experimentellt. Det visas att prestanda är möjlig att förbättra ner mot den teoretiska gräns på 1 μm som erhållits vid systemsimuleringar. Möjligheterna att använda fyllda hålfibrer och polarisationskänslig mätning för detektering av temperaturgränser studeras i syfte att komplettera befintliga fiberoptiska värmedetektorsystem. Förändringen i fiberns dubbelbrytning vid övergångstemperaturen mellan vätske- och fast fas för ämnet i hålen visas och bestäms experimentellt för hålfibrer fyllda med vattenlösningar respektive en metallegering, och resultaten understöds också av simuleringar. En punktsensor för temperaturdetektering baserad på denna princip föreslås. Vidare visas principerna för distribuerad detektering genom registrering av förändringen i dubbelbrytning med polarisations-OTDR (POTDR). Det visas att OTDR-teknik med hög spatial upplösning behövs för övervakning av de studerade fibrerna, och hålfibrer utformade med lägre dubbelbrytning föreslås för framtida studier av tillämpningen.
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Leung, Ian Kin-Hay Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Development of composite cavity fibre lasers for fibre laser hydrophone systems." Publisher:University of New South Wales. Electrical Engineering & Telecommunications, 2008. http://handle.unsw.edu.au/1959.4/41248.
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In this thesis, my main focus was to establish a novel composite-cavity fibre laser (CCFL) and to apply it in sensing, particularly in the hydrophone application. The CCFL that I have proposed is formed by writing three wavelength matched fibre Bragg gratings directly into a continuous length of doped fibre. I have also examined the relative advantages and disadvantages of interferometric and intensity-based hydrophone systems, and have established a hydrophone system that can be switched between the two modes of operation, by making use of digital signal processing. I have established a theoretical model to study the lasing and spectral characteristics of the CCFL. My analysis showed that whilst the CCFL have significantly different phase and threshold conditions from the common semiconductor diode lasers with external cavity, the CCFL also have mode-limiting properties that are often sought after. Through simulations, I was able to identify that a non-uniform straining scheme, that is, when one of the sub-cavities of the CCFL is restrained from strain, can improve the sensitivity with respect to existing single cavity fibre lasers, in both the frequency and intensity domains. My simulations also showed that the sensitivity of such a straining scheme can be optimised by tuning the reflectivity of the gratings, sub-cavity lengths, doping concentration and pump power. I have fabricated multiple CCFLs using the in-house grating writing facilities, and have experimentally assessed their power and spectral related lasing characteristics. Whilst having a significantly longer total cavity length compared to typical fibre lasers, the CCFLs demonstrated stable single longitudinal mode operation and narrow linewidth in the order for a few tens of kHz. Asymmetric output power and frequency as a result of unequal sub-cavity lengths were also examined. Finally, I conducted sensing experiments by applying the CCFLs in strain monitoring and intensity-based hydrophone. My results showed that the non-uniform straining scheme had significantly improved the intensity response of the CCFL, and that the acoustic pressure and frequency can be determined by directly sampling and applying Fourier transform to the output intensity of the fibre laser.
18
Hamill, Alan. "Electropolymerisation of luminescent metalloporphyrins and the application of these films to fibre optic oxygen sensing." Thesis, Glasgow Caledonian University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267082.
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Reinsch, Thomas [Verfasser]. "Structural integrity monitoring in a hot geothermal well using fibre optic distributed temperature sensing / Thomas Reinsch." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2012. http://d-nb.info/1028623232/34.
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Austin, Edward Alfred Denzil. "Studies of measurement techniques for indirect chemical sensing based on fluorescence spectroscopy and applications for fibre-optic sensors." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/50196/.
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This thesis describes experimental and theoretical studies of interrogation systems for determining fluorescent decays of order a few microseconds. The studies have enabled optimised design of interrogators for sensing oxygen using a fluorescent polymerencapsulated ruthenium complex. Two basic interrogation methods were explored, using blue LED excitation. The Rapid Lifetime Detection (RLD) scheme, a fluorescence interrogation method based on direct interrogation of the decay curve following pulsed excitation was generalised, and a novel method for optimising measurement precision derived. The effect of background light on the optimum was quantified. Dissolved (aqueous) oxygen concentration was measured to a precision of 1 part per billion using a 1 second response time (the peak fluorescence power was only 12.5±0.5pW). A second interrogation method, where the phase delay between an intensity modulated excitation source and the resultant fluorescence is processed to make measurements, was for the first time, fully analysed for measurement of exponential decays. When measuring fluorescence lifetimes in the range 2.9-3.3μs, a precision of 2.3 x 10-10 s Hz-0.5 was achieved. (The peak fluorescence power was 500±25pW). A novel combination of ruby optical temperature sensor insert and oxygen sensing layer was demonstrated as a simultaneous temperature and oxygen sensor. A new fluorescence calibration standard consisting of thermally stabilised titanium-dopedsapphire sample was constructed to calibrate and test the indicators. This work was sponsored by a BRITE EuRam European project, which helped determine the priorities of the research.
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Liehr, Sascha [Verfasser], Klaus [Gutachter] Petermann, Brian [Gutachter] Culshaw, and Christian-Alexander [Gutachter] Bunge. "Fibre Optic Sensing Techniques Based on Incoherent Optical Frequency Domain Reflectometry / Sascha Liehr ; Gutachter: Klaus Petermann, Brian Culshaw, Christian-Alexander Bunge." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2015. http://d-nb.info/1122648006/34.
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Koob, Christopher E. "High temperature fiber optic strain sensing." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-02132009-171339/.
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Bennett, Kimberly Dean. "Fiber optic techniques for remote sensing." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/104293.
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Lyu, Chang Y. "Automated infrared fiber optic characterizer." Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/51917.
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Recent progress in reducing the extrinsic losses of fluorozirconate optical fibers has increased the material research efforts for these new waveguides. Fluorozirconate fibers, which are inherently more transparent than silica fibers, are predicted to have intrinsic losses as low as 0.001 dB/km at 3.45 μm [11]. Unfortunately, high intrinsic losses still plague these new optical fibers and these losses must be understood before ultra-low loss fibers become a reality. An automated fiber optic characterizer can help determine the loss mechanisms and the optical properties of fluorozirconate fibers so extrinsic loss mechanisms can be understood and eventually controlled. The automated fiber optic characterizer can also speed up the measurement process by using a microcomputer to align the fiber, calculate the results, and plot the graph. This thesis presents the technical issues involved in the design and construction of an automated infrared fiber optic characterizer. The thesis also outlines the test results of a constructed automated fiber optic characterizer. The characterizer measures spectral attenuation between 0.8 μm and 4 μm, differential modal attenuation between 1.6 μm and 4 μm, and numerical aperture at 1.55 μm and 2.55 μm.Master of Science
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Malik, Asif. "A dual wavelength fiber optic strain sensing system." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-03032009-040724/.
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Seng, Frederick Alexander. "Body Armor Shape Sensing with Fiber Optic Sensors." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6950.
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In this dissertation, the rate of the BFD during body armor impact is characterized with fiber Bragg gratings for the first time ever. The depth rate is characterized using a single fiber optic sensor, while the entire shape rate can be characterized using multiple fiber optic sensors. This is done with a final depth accuracy of less than 10% and a timing accuracy of 15% for BFDs as deep as 50 mm and impact event of less than 1 millisecond. The shape sensing method introduced in this dissertation is different from traditional fiber optic sensor shape reconstruction methods in the fact that strain from the kinetic friction regime is used rather than the static friction regime. In other words, information from the fiber optic sensors slipping is used to reconstruct the shape in this work, whereas strain from the fiber optic sensor remaining fixed to a reference is used for typical fiber optic shape sensing purposes.
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Marques, Carlos Alberto Ferreira. "Fiber-optic components for optical communicatios and sensing." Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12218.
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Doutoramento em Engenharia FísicaNos últimos anos, a Optoelectrónica tem sido estabelecida como um campo de investigação capaz de conduzir a novas soluções tecnológicas. As conquistas abundantes no campo da óptica e lasers, bem como em comunicações ópticas têm sido de grande importância e desencadearam uma série de inovações. Entre o grande número de componentes ópticos existentes, os componentes baseados em fibra óptica são principalmente relevantes devido à sua simplicidade e à elevada de transporte de dados da fibra óptica. Neste trabalho foi focado um destes componentes ópticos: as redes de difracção em fibra óptica, as quais têm propriedades ópticas de processamento únicas. Esta classe de componentes ópticos é extremamente atraente para o desenvolvimento de dispositivos de comunicações ópticas e sensores. O trabalho começou com uma análise teórica aplicada a redes em fibra e foram focados os métodos de fabricação de redes em fibra mais utilizados. A inscrição de redes em fibra também foi abordado neste trabalho, onde um sistema de inscrição automatizada foi implementada para a fibra óptica de sílica, e os resultados experimentais mostraram uma boa aproximação ao estudo de simulação. Também foi desenvolvido um sistema de inscrição de redes de Bragg em fibra óptica de plástico. Foi apresentado um estudo detalhado da modulação acústico-óptica em redes em fibra óptica de sílica e de plástico. Por meio de uma análise detalhada dos modos de excitação mecânica aplicadas ao modulador acústico-óptico, destacou-se que dois modos predominantes de excitação acústica pode ser estabelecidos na fibra óptica, dependendo da frequência acústica aplicada. Através dessa caracterização, foi possível desenvolver novas aplicações para comunicações ópticas. Estudos e implementação de diferentes dispositivos baseados em redes em fibra foram realizados, usando o efeito acústico-óptico e o processo de regeneração em fibra óptica para várias aplicações tais como rápido multiplexador óptico add-drop, atraso de grupo sintonizável de redes de Bragg, redes de Bragg com descolamento de fase sintonizáveis, método para a inscrição de redes de Bragg com perfis complexos, filtro sintonizável para equalização de ganho e filtros ópticos notch ajustáveis.
In the last years, the Optoelectronics has been established as a top field of research able to drive towards new technological solutions. The abundant achievements in the field of optics as well in optical communications have been of great importance and triggered a number of innovations. Among the large group of existing optical components, optical fiber components are mainly relevant due to three factors: their simplicity, their nature as an optical fiber based component and the capability of optical fiber to carry information. In this thesis the focus was on one of these optical components: optical fiber gratings, which have unique optical processing properties and are quite interesting for the development of devices for optical communications and sensing applications. The work started with a theoretical analysis applied to fiber gratings and continues with the most used fiber gratings production methods. The inscription of fiber gratings was also addressed in this work, where an automated inscription setup has been implemented for silica fiber, and experimental results showed a good approximation to the simulation study. Also, the inscription setup for gratings in polymer optical fiber was developed. A detailed analysis of the acousto-optic modulation in fiber gratings in silica and polymer optical fiber was presented. By means of a detailed analysis of the mechanical excitation modes applied to the modulator set, it was noticed that two predominant modes of acoustic excitation can be found in the optical fiber depending on the applied acoustic frequency. Through this characterization, it was possible to develop new applications. Studies and implementation of different devices based on fiber gratings were performed, using acousto-optic effect and regeneration process in optical fiber for photonic applications such as fast add-drop multiplexer, tunability of the fiber Bragg grating group delay, tunable phase-shift fiber Bragg grating, tunable mode coupler, method for inscription of complex fiber Bragg grating profiles, gain equalization filter and adjustable notch filters.
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Nagarajan, Anjana. "Chemical sensing applications of fiber optics." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07102009-040555/.
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Seng, Frederick Alexander. "An Exploration in Fiber Optic Sensors." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6101.
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With the rise of modern infrastructure and systems, testing and evaluation of specific components such as structural health monitoring is becoming increasingly important. Fiber optic sensors are ideal for testing and evaluating these systems due many advantages such as their lightweight, compact, and dielectric nature. This thesis presents a novel method for detecting electric fields in harsh environments with slab coupled optical sensors (SCOS) as well as a novel method for detecting strain gradients on a Hopkinson bar specimen using fiber Bragg gratings (FBG). Fiber optic electric field sensors are ideal for characterizing the electric field in many different systems. Unfortunately many of these systems such as railguns or plasma discharge systems produce one or more noise types such as vibrational noise that contribute to a harsh environment on the fiber optic sensor. When fiber optic sensors are placed in a harsh environment, multiple noise types can overwhelm the measurement from the fiber optic sensor. To make the fiber optic sensor suitable for a harsh environment it must be able to overcome all these noise types simultaneously to operate in a harsh environment rather than just overcome a single noise type. This work shows how to eliminate three different noise types in a fiber optic sensor induced by a harsh environment simultaneously. Specifically, non-localized vibration induced interferometric noise is up converted to higher frequency bands by single tone phase modulation. Then localized vibrational noise, and radio frequency (RF) noise are all eliminated using a push-pull SCOS configuration to allow for an optical measurement of an electric field in a harsh environment. The development and validation of a high-speed, full-spectrum measurement technique is described for fiber Bragg grating sensors in this work. A fiber Bragg grating is surface mounted to a split Hopkinson tensile bar specimen to induce high strain rates. The high strain gradients and large strains which indicate material failure are analyzed under high strain rates up to 500 s-1. The fiber Bragg grating is interrogated using a high-speed full-spectrum solid state interrogator with a repetition rate of 100 kHz. The captured deformed spectra are analyzed for strain gradients using a default interior point algorithm in combination with the modified transfer matrix approach. This work shows that by using high-speed full-spectrum interrogation of a fiber Bragg grating and the modified transfer matrix method, highly localized strain gradients and discontinuities can be measured without a direct line of sight.
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Fan, Ning Yao. "Development of fiber optic sensing techniques for structural assessment." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0027/NQ33900.pdf.
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Vengsarkar, Ashish Madhukar. "Novel microbend loss fiber optic hydrophones for direction sensing." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43065.
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Dual purpose fiber optic microbend loss sensors have been developed for
measurement of underwater acoustic wave amplitudes and for detection of the
direction of wave propagation. Cylindrical sensing elements with external threads
have fibers wound around them. Axial slots, cut along the length of the cylinder
and deeper than the threads, provide the microbends. Three different
construction schemes for cylindrical sensing elements are built. The dual purpose
hydrophones are characterized for frequencies ranging from 15 kHz to 75 kHz.
Based on the results, an improved design that uses the wavelength dependence
of microbend loss in a single mode fiber is proposed.Master of Science
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Cartwright, Abigail E. (Abigail Elaine). "Optimization of a fiber optic freshwater DOM sensing device." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123217.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (page 27).
Fiber optical arrangements are useful for measurement of aquatic chemical species, especially in waters of high chemical concentrations. An optical fiber spectrofluorometer device known as the "Hammerhead" was developed in the Hemond lab in 2015 and improved in 2016 to measure concentrations of dissolved organic matter in water samples. The Hammerhead operates by detecting fluorescence, absorbance, and scattering of light within the water. However, inner shielding, particularly in high DOC concentrations, can lead to meaningless results. This project expands upon the earlier Hammerhead work by seeking the highest possible fluorescence signal from the Hammerhead. Experiments were run using a series of different geometric schemes for the Hammerhead optical fibers. Of the configurations tested, the narrowest spacing between excitation fiber and detector (0.076 inches from each fiber's tip to the center of the chamber) produced optimal results. This new configuration shortens the light path length and largely avoids inner shielding effects. The new design was then compared with a traditional flow cell water measurement device known as the LEDIF, using both fluorescein and humic acid substances. Comparing the signals for both instruments indicates that the Hammerhead fiber optic scheme is superior in detecting fluorescence measurements at high DOC concentrations; it produces a nearly linear response for fluorescence, while inner shielding hinders LEDIF results. In addition, comparing the limit of detection for both instruments indicates that the Hammerhead performs better than the LEDIF even independent of inner shielding effects, producing a signal nearly 10 times greater than the LEDIF in low DOC concentrations.
by Abigail E. Cartwright.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering
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Yu, Guo. "Sapphire Based Fiber-Optic Sensing for Extreme High Temperatures." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/76982.
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Temperature sensing is one of the most common and needed sensing technique, especially in harsh environment like a coal gasifier or an airplane engine. Single crystal sapphire has been studied in the last two decades as a candidate for harsh environment sensing task, due to its excellent mechanical and optical properties under extreme high temperature (over 1000°C).
In this research, a sapphire wafer based Fabry-Perot (FP) interferometer sensor has been proposed, whose functional temperature measurement can go beyond 1600°C. The size of the sensors can be limited to a 2cm-length tube, with 2mm outer diameter, which is suitable for a wide range of harsh environment applications. The sensors have shown linear sensing response during 20~1200°C temperature calibration, with high sensitivity and resolution, and strong robustness, which are ready for the field test in real-world harsh environment.Master of Science
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Liang, Xiao. "In-Line Fiber Optic Sensing System for Pipeline Corrosion Detection." Thesis, North Dakota State University, 2015. https://hdl.handle.net/10365/27903.
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To understand the impact of corrosion on metal on-shore buried transmission pipeline, which is one of the most critical damages, corrosion evaluation plays an important role. An effective approach for real-time in-line detection of corrosion is still not fully developed yet. This study introduces a concept of using an in-line optical fiber sensor system embedded inside metallic corrosion-resistant coating to conduct corrosion detection. Fiber Bragg grating sensors were selected as sensing units and the metallic corrosion-resistant coating was achieved using the high velocity oxygen fuel thermal spraying technique. The successful embedment technique was developed by using stainless steel adhesive protection during coating process. Accelerated corrosion tests were performed on four coated steel plate samples with embedded sensors. Both electrochemical and the embedded sensing system were used to assess the corrosion status of the samples. The test results proved the possibility of this method which can potentially apply for metal pipelines.
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Elvin, Niell Glen. "Subsurface damage detection using a novel fiber optic sensing technique." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50510.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1998.Includes bibliographical references (p. 107-110).
The detection of subsurface damage is important in ensuring the safety and timely repair of structures. Existing methods for non-destructive evaluation of structural elements tend to be either expensive or unreliable for monitoring large scale systems. The novel fiber optic based technique developed in this research overcomes many of the limitations of traditional non-destructive evaluation methods by providing an interferometric sensing technique coupled with a simple mechanical test. The method is based on monitoring the phase change in an integral interferometric fiber optic sensor caused by moving a mechanical load over the damaged structure. The method has been shown to unambiguously detect both the position and size of damage. The theoretical and experimental validation of the proposed method is presented for the case of open cracks in which the faces are not allowed to come into contact. The effect of damage position and damage size on sensor performance for two typical structural elements is also presented. A closed loop fiberoptic interferometer with modulated load is shown to overcome the traditional problems of environmental drift such as material creep, temperature and ambient noise. This interferometric technique is also shown to be one of the few fiber-optic based techniques that have adequate sensitivity for integral damage detection. Many traditional non-destructive evaluation methods tend to be insensitive in detecting closed cracks. Thus the closed crack problem represents a special challenge for structural damage monitoring. A fast iterative based boundary element method has been developed to solve this problem. This method is used to show the theoretical feasibility of detecting closed cracks with the developed novel sensing method.
by Niell Elvin.
Ph.D.
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Bae, Taehan. "Fiber optic sensing technology for measuring in-cylinder pressure in automotive engines." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4253.
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A new fiber optic sensing technology for measuring in-cylinder pressure in
automotive engines was investigated. The optic sensing element consists of two
mirrors in an in-line single mode fiber that are separated by some distance. To
withstand the harsh conditions inside an engine, the Fiber Fabry-Perot Interferometer
(FFPI) element was coated with gold and copper. The metal-protected fiber sensor
was embedded into a small cut in the metal casing of the spark plug. At first, the
sensing element was dipped in liquid gold and cured. Then the gold-coated fiber
sensor was electroplated with copper. Finally, the metal-coated fiber sensor was
embedded in the spark plug.
The spark-plug-embedded FFPI sensor was monitored using a signal
conditioning unit. Field tests were carried out in a 3-cylinder automotive engine with
a piezoelectric pressure sensor as a reference transducer up to about 3500 rpm. The
fiber optic sensor data generally matched those measured by the piezoelectric
reference sensor. The use of a Vertical Cavity Surface Emitting Laser (VCSEL) diode as a light
source in an FFPI optic sensor system was investigated. Reflected light from the FFPI
sensing element was used to measure the optical path difference.
With a 1550nm VCSEL as the light source in a 12mm cavity length Fiber
Fabry-Perot Interferometer, spectral characteristics were examined to determine the
proper combination of dc bias current, modulation current amplitude and modulation
frequency. Single VCSEL operation and regular fringe patterns were achieved.
The laser tuning was -41.2 GHz/mA and was determined from measurements
of the shift in the spectral peak of the VCSEL diode output as a function of dc bias
current. By testing the fringe movement as the FFPI sensor was heated, the
temperature tuning coefficient for the optical length was determined to be 11 x 10-6 úC.
The results of these experiments indicate that the use of VCSEL diode as a
light source for the FFPI sensor offers a viable alternative to the use of Distributed
Feedback (DFB) laser diodes for monitoring at a lower bias current and modulating
current amplitude.
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Minasamudram, Rupa Gopinath Daryoush Afshin Samimi. "Optimization of wideband fiber optic hydrophone probe for ultrasound sensing applications /." Philadelphia, Pa. : Drexel University, 2010. http://hdl.handle.net/1860/3319.
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Baldwin, Christopher S. "Distributed sensing for flexible structures using a fiber optic sensor system." College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/288.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2003.Thesis research directed by: Mechanical 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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White, Julia. "OPTIC FIBER SENSOR FOR STRAIN MEASUREMENTS IN HIGH TEMPERATURE SENSING APPLICATIONS." International Foundation for Telemetering, 2017. http://hdl.handle.net/10150/626969.
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Optic fiber sensors are employed in a variety of applications for the remote measurement of various parameters such as strain, pressure, or temperature. These sensors offer an array of benefits as well including light weight, compactness, and high resolution. In particular, Fabry-Perot interferometers (FPIs) maintain these benefits and can also be made to withstand extremely high temperatures. This advantage of the FPI allows it to be used in harsh environments where many other tools for parameter measurement could not survive. An FPI strain sensor is constructed and tested which has the capabilities to be used at high temperatures of over 1000°C for applications in gas turbine engine testing. This paper discusses the need for high temperature strain sensors in engine testing and this sensor’s capabilities in this application.
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Kateklum, Rutjaphan. "Fiber optic fluorescence pH sensing for biomedical applications : theoretical and experimental studies." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD048.
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Les fonctions organiques du corps humain sont liées à des constants biologiques. Variations de ces constantes induisent divers états pathologiques. Parmi ces constantes, le pH constitue le cœur de ces travaux de thèse. Chez les êtres vivants, les fonctions biologiques dépendent de constant acides ou alcalines. En fait, l’action d’une protéine dépend du pH du milieu environnant. Une valeur inadéquate du pH rend les protéines inactives ce qui est délétère pour l’organisme. Il existe donc un besoin pour des capteurs de pH qui puissant être utilisés dans le corps humain pour des applications cliniques (échelle macroscopique), sur des cellules en culture pour des recherches en biologie (échelle mesoscopique) et pour étudier les échanges ioniques au niveau des membranes cellulaires pour des travaux plus fondamentaux (échelle microscopique). Parmi le large éventail de technologies potentiellement candidates pour ces applications, la mesure de pH par fibre optique exploitant la fluorescence permet d’être adaptée aux trois échelles dimensionnelles susnommées. Ce manuscrit de thèse adresse des contraintes par l’étude de capteurs fluorescents à fibre optique utilisant deux types d’indicateur de pH: les SNARF et la fluorescéine. En parallèle de ces développements expérimentaux, des descriptions mathématiques des propriétés de fluorescence de ces deux indicateurs sont proposées. Ces descriptions permettent de progresser vers une mesure du pH sans calibrationOrganic functions of the human body are linked to biological constants. Variations of these constants induce pathological troubles. Among these constants, the pH is the central subject of this PhD work. In living beings, biological functions are related to either acid or alkaline constants. Indeed, the action of a protein depends on the surrounding pH. An inadequate value of the pH makes the proteins non active which is deleterious for the organism. There exist a need for pH sensors which can be used in the human body for clinical applications (macroscopic scale), on cells in culture for biology researches (mesoscopic scale) or at a cell membrane level for more fundamental studies (microscopic scale). Among the wide range of technologies potentially useful for these applications, fiber optic fluorescence pH sensing offers the possibility to be adapted to the three above mentioned dimensional scales. This PhD dissertation addresses these constraints by studying fluorescence fiber optics pH sensors using two kind of pH indicators: SNARF and fluorescein. Together with these experimental studies, mathematical descriptions of the fluorescence properties of these indicators are proposed. They allow progressing towards calibration free pH sensing
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Bassil, Antoine. "Distributed fiber optics sensing for crack monitoring of concrete structures." Thesis, Nantes, 2019. http://www.theses.fr/2019NANT4057.
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Le travail de thèse présenté dans ce mémoire vise à développer et valider une technique de suivi d’ouvertures de fissures à l'aide de mesures réparties de déformation par fibres optiques. Dans un premier temps les différentes théories existantes sur le transfert de déformation du matériau hôte vers la fibre optique sont présentées avec leurs domaine de validité. Le problème de l’adhésion parfaite entre couche est ensuite étudié et un modèle analytique à trois couches tenant compte d’une adhésion imparfaite est élaboré. Ce modèle est ensuite généralisé aux systèmes multicouches. Les études expérimentales validant ce nouveau modèle sont alors présentées. Elles montrent qu’il est possible de suivre les ouvertures de fissures jusqu’à 1000 μm avec une erreur inférieure à 10% avec un câble à fibre optique collé en surface. Les câbles noyés dans le béton donnent des résultats moins justes. La justesse des mesures est aussi influencée par le type de câble, la longueur d’ancrage et le durcissement du béton. Enfin, les résultats des études de cas sur des échantillons en béton armé de laboratoire sont présentés. Elles montrent la capacité des fibres à détecter des fissures aussi précocement que les capteurs acoustiques à ultrasons et de surveiller l’ouverture de micro fissures multiplesThis thesis work aims to develop and validate a method for monitoring crack openings using distributed fiber optics strain measurements. First, the various existing theories on strain transfer from the host material to the optical fiber are presented, with their validity domain. The problem of perfect interfacial bonding is then studied and a three-layer analytical model capable of handling imperfect bonding case is proposed. This model is then generalized to multi-layer systems. Experimental studies validating this new model are presented. They show that it is possible to monitor crack openings up to 1 mm with an error of less than 10% for a fiber optic cable glued on the surface. Cables embedded in concrete show less accurate results. The type of cable, the bonding length and the hardening of the concrete material also influence the accuracy of the estimated crack openings. Finally, the results of case studies on laboratory-size reinforced concrete samples are presented. They show the optical fibers capacity to detect cracks as early as ultrasonic sensors and to monitor the opening of multiple micro cracks
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Wang, Yunjing. "Fiber-Optic Sensors for Fully-Distributed Physical, Chemical and Biological Measurement." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19222.
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Distributed sensing is highly desirable in a wide range of civil, industrial and military applications. The current technologies for distributed sensing are mainly based on the detection of optical signals resulted from different elastic or non-elastic light-matter interactions including Rayleigh, Raman and Brillouin scattering. However, they can measure temperature or strain only to date. Therefore, there is a need for technologies that can further expand measurement parameters even to chemical and biological stimuli to fulfill different application needs. This dissertation presents a fully-distributed fiber-optic sensing technique based on a traveling long-period grating (T-LPG) in a single-mode fiber. The T-LPG is generated by pulsed acoustic waves that propagate along the fiber. When there are changes in the fiber surrounding medium or in the fiber surface coating, induced by various physical, chemical or biological stimuli, the optical transmission spectrum of the T-LPG may shift. Therefore, by measuring the T-LPG resonance wavelength at different locations along the fiber, distributed measurement can be realized for a number of parameters beyond temperature and strain.
Based on this platform, fully-distributed temperature measurement in a 2.5m fiber was demonstrated. Then by coating the fiber with functional coatings, fully-distributed biological and chemical sensing was also demonstrated. In the biological sensing experiment, immunoglobulin G (IgG) was immobilized onto the fiber surface, and the experimental results show that only specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the T-LPG when it passes through the pretreated fiber segment. In the hydrogen sensing experiment, the fiber was coated with a platinum (Pt) catalyst layer, which is heated by the thermal energy released from Pt-assisted combustion of H2 and O2, and the resulted temperature change gives rise to a measurable T-LPG wavelength shift when the T-LPG passes through. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This technique may also permit measurement of other quantities by changing the functional coating on the fiber; therefore it is expected to be capable of other fully-distributed sensing applications.
Ph. D.
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Song, Jia. "Optical Frequency Domain Reflectometry: Sensing Range Extension and Enhanced Temperature Sensitivity." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31532.
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Optical fiber sensors have attracted tremendous attention over last two decades and have been successfully employed in various sensing applications, including temperature, strain, current, and so on. Among all types of optical fiber sensors, optical frequency domain reflectometry (OFDR) has been widely studied for its merits of simple configurations, high spatial resolution and high sensing accuracy. However, current limitation on OFDR lies in the sensing range and sensing accuracy. The state of art performance of commercial OFDR provides ~70m sensing range as well as 0.1K temperature accuracy. This is not adequate for large building distributed health monitoring due to the limited sensing range. Besides, high temperature response is also on demand for high precision measurement. To resolve the above limitation, in this thesis two major subjects have been studied regarding improving the performance and applicability of OFDR: One aims at extending the sensing range of OFDR while the other one focuses on enhancing temperature sensitivity of OFDR.
Firstly, we proposed novel data resampling approach regarding tuning nonlinearities of laser source to extend the sensing range. Commercial OFDR employs auxiliary interferometer (AI) to trigger data acquisition, where the maximum sensing range is limited to a quarter of the optical path difference (OPD) of AI according to Nyquist Sampling theorem. By employing the data resampling algorithm, the sensing range is no longer restricted by OPD and can even reach laser coherent length since OFDR is based on coherent detection scheme. Three data resampling algorithms are individually discussed and a sensing range of ~300m (~4 times the sensing range of commercial OFDR) with 8cm spatial resolution is for the first time achieved.
Secondly, the temperature response of OFDR is enhanced and we successfully achieved high temperature accuracy distributed sensing. One advantage of high temperature response is to enhance the spatial resolution since less spatial points are required in performing cross-correlation, while the other advantage is to obtain high temperature accuracy measurement at the same spatial resolution compared to that of traditional OFDR. This is especially important for maintaining spatial resolution under long range OFDR sensing since the total wavelength tuning range is smaller than traditional OFDR. Commonly the temperature response of single mode fiber is contributed by both thermal expansion coefficient and thermal optic coefficient of the waveguide and can be enhanced by increasing either of those coefficients. Thermal expansion coefficient is related with material property and is a weighted value of both bare fiber and coating. By using a large thermal expansion coefficient acrylic plank as a “coating” on SMF, we achieved ~9 times temperature response (~95 pm/ ˚C) compared with SMF (~10 pm/ ˚C). Further experiment is demonstrated with small diameter taper on an acrylic plank “coating”, in which case both thermal expansion coefficient and thermal optic coefficient are raised and a ~20 times temperature response than SMF (~200 pm/˚C) is obtained. This is especially meaningful for its easy fabrication, low cost and extremely high temperature response and leads to practical usage for high accuracy distributed temperature sensing.
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Brown, Kevin S. "Embedded Distributed Fiber Optic Strain Measurements for Delamination Detection in Composite Laminates." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1543330547266239.
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Rhee, Sang-Yoon. "An investigation of forward transmissive quasi-distributed fiber optic sensing for dual parameter measurement /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu148640189520653.
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Liu, Bo. "Sapphire Fiber-based Distributed High-temperature Sensing System." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82741.
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From the monitoring of deep ocean conditions to the imaging and exploration of the vast universe, optical sensors are playing a unique, critical role in all areas of scientific research. Optical fiber sensors, in particular, are not only widely used in daily life such as for medical inspection, structural health monitoring, and environmental surveillance, but also in high-tech, high-security applications such as missile guidance or monitoring of aircraft engines and structures. Measurements of physical parameters are required in harsh environments including high pressure, high temperature, highly electromagnetically-active and corrosive conditions. A typical example is fossil fuel-based power plants. Unfortunately, current optical fiber sensors for high-temperature monitoring can work only for single point measurement, as traditional fully-distributed temperature sensing techniques are restricted for temperatures below 800°C due to the limitation of the fragile character of silica fiber under high temperature.
In this research, a first-of-its-kind technology was developed which pushed the limits of fully distributed temperature sensing (DTS) in harsh environments by exploring the feasibility of DTS in optical sapphire waveguides. An all sapphire fiber-based Raman DTS system was demonstrated in a 3-meters long sapphire fiber up to a temperature of 1400°C with a spatial resolution of 16.4cm and a standard deviation of a few degrees Celsius.
In this dissertation, the design, fabrication, and testing of the sapphire fiber-based Raman DTS system are discussed in detail. The plan and direction for future work are also suggested with an aim for commercialization.Ph. D.
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Perry, Daniel Theodore. "Directional Electric Field Sensing Using Slab Coupled Optical Fiber Sensors." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3443.
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This thesis provides the details of a multi-axis electric field sensor. The sensing element consists of three slab coupled optical fiber sensors that are combined to allow directional electric field sensing. The packaged three-axis sensor has a small cross-sectional area of 0.5 cm x 0.5 cm achieved by using an x-cut crystal. The method is described that uses a sensitivity-matrix approach to map the measurements to field components. The calibration and testing are described resulting in an average error of 1.5º.This work also includes a description of the packaging method used as well as a thorough analysis of the directional sensitivity of potassium titanyl phosphate (KTP) and electro-optic polymer: the two materials used as sensing elements. Each of the two materials is highly direction sensitive creating minimal crosstalk between the sensors.
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Su, Xu. "Design and Evaluation of Off-centered Core Fiber for Gas Sensing." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99348.
Full textAbstract:
Gas Sensing Has Become a Very Important and Attractive Technique Because of Its Various Applications, Such as in the Increasingly Concerning Case of Environmental Issues, Automobile Emission Detection, Natural Gas Leakage Detection, Etc. It Also Has Significant Applications in Industries, Such as Safety and Health Monitoring in Underground Mines. Among Those Sensing Areas, Fiber-optic Sensors Have Drawn Considerable Attention Because of Its Small Size, Light Weight, High Sensitivity, and Remote Sensing Capability. However, Current Fiber-optic Gas Sensing Techniques Have Several Limitations on Their Potential for Multiplexed or Distributed Sensing Due to Difficulties Such as High Complexity or Large Loss.
To Accomplish the Goal for Multiplexed Gas Sensing, an Off-centered Core Fiber Design Is Investigated. The Eccentric Core Can Reduce Attenuation, Keep Mechanical Strength, and Lower Fabrication Cost. To Verify the Feasibility of the Design, Fiber Field Distribution Is First Studied in Simulation, Which Will Be Discussed in Detail in Chapter 2. Then Two Fiber Samples with a Length of 10 Cm and 40 Cm Are Prepared and Placed in a Custom Methane Sensing System for Gas Absorption Testing, Which Is Detailed in Chapter 3. From Etching Analysis, Localized Surface Defects Are Found as the Main Reason for Power Loss. Performance Such as Detection Resolution and Sensitivity Are Investigated. In Chapter 4, Theoretical Evaluations Have Been Conducted for Multiplexed Sensors Performances Using the Off-centered Core Fiber to Study the Impact Fiber Parameters on Sensing System Design. The Conclusion and Summary Are Presented in Chapter 5.Master of Science
Gas Sensing Has Become a Very Important and Attractive Technique Because of Its Various Applications, Such as in the Increasingly Concerning Case of Environmental Issues, Automobile Emission Detection, Natural Gas Leakage Detection, Etc. It Also Has Significant Applications in Industries, Such as Safety and Health Monitoring in Underground Mines. Among Those Sensing Areas, Fiber-optic Sensors Have Drawn Considerable Attention Because of Its Small Size, Light Weight, High Sensitivity, and Remote Sensing Capability. However, Current Fiber-optic Gas Sensing Techniques Have Several Limitations on Their Potential for Long Distance Distributed Sensing Due to Difficulties Such as High Fabrication Complexity. In This Work, a Fiber-optic Gas Sensor with Special Structure Was Designed. The Sensor Can Reduce Attenuation, Keep Mechanical Strength, and Lower Fabrication Cost. To Verify the Feasibility of the Design, Theory Analysis and Simulation Were Conducted, Which Will Be Discussed in Detail in Chapter 2. Then Two Samples with a Length of 10 Cm and 40 Cm Were Prepared and Placed in a Custom Methane Sensing System for Testing. And Their Performance Such as Sensitivity Is Investigated. In Chapter 4, Theoretical Evaluations Have Been Conducted for Multiplexed Sensors Performances Evaluation to Study the Impact Fiber Parameters on Sensing System Design. The Conclusion and Summary Are Presented in Chapter 5.
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Gibson, Richard S. "Slab-Coupled Optical Fiber Sensors for Electric Field Sensing Applications." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3248.pdf.
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Montero, Ryan M. "Analysis, Design and Testing of a Wind Tunnel Model to Validate Fiber-Optic Shape Sensing Systems." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23233.
Full textAbstract:
The ability to collect valuable data concerning the stress, strains, and shape profiles of aircraft and aircraft components during flight is important to fields such as structural health monitoring, gust alleviation, and flutter control. A research interest in the form of a NASA PhaseI SBIR called for possible systems that would be able to take accurate shape sensing data on a flexible wing aircraft. In a joint venture between Luna Technologies Inc. and Virginia
Polytechnic Institute and State University a flexible wing wind tunnel model was designed and constructed as a test article for the Luna Technologies Inc. fiber optic shape sensing system. In order to prove the capability of a fiber optic shape sensing system in a wind tunnel environment a flexible wing test article was constructed. The wing deflections and twists of the test article were modeled using a vortex lattice method called Tornado combined with simple beam theories. The beam theories were linear beam theories and the stiffness of the composite bodies was supplied by static testing of the test articles. The code was iterative in that it ran the VLM code to estimate the forces and moments on the wing and these were applied to a linear beam which gave the wing a new geometry which in turn was run through the VLM. The wind tunnel model was constructed at Virginia Tech using 3-D printing techniques for the fuselage and foam and fiberglass for the wings. On the bottom surface of the wings the Luna Technologies Inc. fiber optic shape sensing fiber was bonded along the leading and tailing edges. The swept-wing test article was experimentally tested in the Virginia Tech 6\'x6\' Stability Wind Tunnel at various airspeeds and the VLM based code results were in agreement, within margins of error and uncertainty, with the experimental results. The agreement of the analytical and experimental results verified the viability of using an iterative VLM code in combination with simple beam theories as a quick and relatively accurate approximation method for preliminary design and testing. The tests also showed that a fiber optic shape sensing system can be sufficiently tested in a wind tunnel environment, and if applied carefully could perhaps in the future provide useful shape and strain measurements.
Master of Science