Dissertations / Theses on the topic 'Optical fibre sensors'
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1
Bristow, Julian Paul Gregory. "Integrated optical components for optical fibre sensors." Thesis, University of Glasgow, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329519.
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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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Inci, M. Naci. "Optical coatings for fibre optic sensors." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1455.
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4
Smith, Richard. "Optical fibre sensors for radioactive environments." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318305.
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5
Tubb, Andrew John Colwill. "Optical fibre surface plasma wave sensors." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624855.
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Geiger, Harald. "Quasi-distributed optical fibre strain sensors." Thesis, University of Southampton, 1995. https://eprints.soton.ac.uk/399104/.
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This thesis presents for the first time two complementary techniques to monitor the optical path length in optical fibre over both long and short sensing lengths. Both techniques may be used to measure the physical environment of the optical fibre, in particular strain and temperature, and are suitable for multiplexed operation. Signal-to-noise analysis shows that current optical time domain reflectometry (OTDR) systems do not fully exploit the spatial resolution theoretically available. A new OTDR technique exploits the theoretical findings to monitor the range of reflective markers in an optical fibre. Measuring strain in fibre sections of several metres is demonstrated. 100?m spatial resolution has been achieved with a pulse duration equivalent to 1 m fibre length and within one second measurement time. The first fibre Bragg grating interrogation system using an acousto-optic tunable filter (AOTF) is described. The interrogation system locks the AOTF wavelength to the wavelength of a selected grating. Measuring the frequency of the AOTF control signal provides an accurate measurement of the grating wavelength. A detailed system analysis is presented to enable the optimisation of system parameters. A wavelength resolution corresponding to 0.4 microstrain is achieved within 0.1sec measurement time, close to the resolution predicted by the system model. This technique allows the use of fibre gratings as sensors for the measurement of both quasi-static and dynamic strains. The combination of the two systems facilitate the utilisation of optical fibre to monitor a structure both over a few metres and at critical points. Both sensor types offer new measurement possibilities as embedded structure monitors, for example for in-service health and usage monitoring or as nerves for active control of smart structures.
7
Volanthen, Mark. "Multiplexed and distributed optical fibre sensors." Thesis, University of Southampton, 1997. https://eprints.soton.ac.uk/394567/.
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This thesis presents three novel optical fibre sensor systems which monitor optical path lengths. The systems have been used to measure strain in an optical fibre. All three systems make several measurements at different locations along a fibre, allowing the spatial distribution of a measurand to be obtained. For the first time, incoherent optical frequency domain reflectometry is used together with time division multiplexing to measure the optical path length of an array of fibre sections. Sensing sections are 5m long and are defined by broadband optical reflectors. A closed loop interrogation system is demonstrated to monitor the sensors in real time with an accuracy of 2.1µ(epsilon)/(root)Hz, in good agreement with the theoretically predicted value. Simultaneous monitoring of multiple fibre Bragg grating sensors, several millimetres in length, is also demonstrated by simultaneously generating multiple passbands in a single acousto-optic tunable filter. This is the only technique demonstrated to simultaneously monitor multiple gratings using a single wavelength-tunable device. The first distributed Bragg grating sensor to measure arbitrary strain profiles is also demonstrated. Low-coherence interferometry selects the interrogation position and a tunable filter measures the local wavelength. Two configurations of the technique are presented, which have achieved spatial resolutions of 300µm and real-time strain measurements with 5.4µ(epsilon)/(root)Hz accuracy, showing good agreement with theoretically predicted values. The only grating sensor network to be both distributed and multiplexed is presented together with the first results.
8
Simpson, Alexander George. "Optical fibre sensors and their interrogation." Thesis, Aston University, 2005. http://publications.aston.ac.uk/8006/.
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This thesis describes novel developments in the fabrication and understanding of type IA fibre Bragg gratings, the uses of said gratings as optical sensors and the interrogation of optical sensors using tilted fibre Bragg gratings. This thesis presents the most detailed study of type IA gratings performed to date and provides the basis of a dual grating optical sensor capable of independently measuring strain and temperature. Until this work it was not known how to reliably fabricate type IA gratings or how they would react to high ambient temperatures, nor was it known what effect external parameters such as fibre type, dopant levels, inscription laser intensity, or hydrogenation levels would have on the physical properties of the grating. This comprehensive study has yielded answers to all of these unknowns and produced several unexpected uses for type IA gratings, such as the use of the previously unreported strong loss band at 1400nm to locally heat fibres by optical absorption and thereby fabricate optically tuneable gratings which do not affect directly adjacent standard gratings. Blazed fibre Bragg gratings have been studied in detail and used to produce several high quality prototype sensor interrogation systems yielding stability an accuracy values unsurpassed by similar devices reported in literature. An accurate distribution map of light radiated by blazed gratings is shown for the first time and has been studied in respect of polarisation state showing that for certain easily achievable conditions a blazed grating spectrometer may be deemed to be polarisation insensitive. In a novel implementation of the system, it is shown that the dynamic wavelength range of a blazed grating spectrometer may be at least doubled by superimposing blazed gratings.
9
Jarzebinska, Renata. "Tapered optical fibre sensors employing nanostructured coatings." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/5585.
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Tapered optical fibres have been manufactured, characterised and studied. These are
compact devices made from single-mode optical fibre. A system for producing tapers has
been developed, employing flame heating of the optical fibre and computer controlled
rotation stages to stretch the fibre in a controlled and repeatable fashion.
Subsequently tapered fibres were coated with nanostructured films of materials that change
their optical properties in response to an external stimulus. An investigation of the effect of
depositing chemically sensitive nano-scale films onto tapered optical fibres has been
undertaken. Three different methods of deposition were applied: Langmuir-Blodgett
technique, electrostatic-self-assembly and – for the first time - chemical grafting. Six
different films of materials were deposited onto tapered fibres: 4-[2-(4-dimethylamino-
naphtalen-1-yl)-vinyl]-1-octadecyl-quinolinium iodide (merocyanine dye),
calix[4]resorcinarene, bilayers of poly(allyamine hydrochloride) (PAH) and anionic
tetrakis(4-sulfophenyl)porphine (TSPP), PAH and cyclodextrine, TiO2 nanoparticles
imprinted with ((1-(4-Nitrophenylazo)-2-naphthol (NPAN) compound), polyaniline
(PANI). During the deposition process the light was launched into each fibre and the
evolution of the transmission spectrum observed.
The coated tapers were subsequently investigated for their potential application as
chemical sensors: pH, red-ox, ammonia sensors. The response to a stimulus was
investigated by immersing the coated tapered fibre in an environment containing the
measurand.
The properties of these devices were also used in combination other photonics concepts,
such as fibre Bragg gratings written in the tapered region of a fiber, under investigation
within the Engineering Photonics Group to develop new sensor elements.
10
Badcock, Rodney Alan. "Optical fibre sensors for structural stain monitoring." Thesis, Brunel University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389265.
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Elliott, Nicholas James. "Development of distributed optical fibre chemical sensors." Thesis, Glasgow Caledonian University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270520.
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Smith, Stephen Roy Walter. "Remote optical fibre temperature and groundwater sensing." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266224.
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13
Selli, Raman Kumar. "Fibre optic temperature sensors using fluorescent phenomena." Thesis, City University London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236641.
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14
Liu, Chen. "Advanced optical fibre grating sensors for biochemical applications." Thesis, Bangor University, 2019. https://research.bangor.ac.uk/portal/en/theses/advanced-optical-fibre-grating-sensors-for-biochemical-applications(29757d94-bfe1-4d75-a4db-8563be1a056f).html.
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This thesis describes a detailed study of advanced fibre optic sensors and their applications for label-free biochemical detection. The major contributions presented in this thesis are summarised below. A self-assembly based in-situ layer-by-layer (i-LbL) or multilayer deposition technique has been developed to deposit the 2D material nanosheets on cylindrical fibre devices. This deposition technique is based on the chemical bonding associated with the physical adsorption, securing high-quality 2D materials coating on specific fibre cylindrical surface with strong adhesion as well as a prospective thickness control. Then a " Photonic-nano-bio configuration", which is bioprobes immobilised 2D-(nano)material deposited fibre grating, was built. 2D material overlay provides a remarkable analytical platform for bio-affinity binding interface due to its exceptional optical and biochemical properties. EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) and NHS (NHydroxysuccinimide) were used to immobilise bioprobes. This kind of configuration is considered to have many advantages such as: enhanced RI sensitivity, enrich immobilisation sites, improved binding efficiency, selective detection. Followed by this configuration, several label-free biosensors were developed. For example, graphene oxide coated dual-peak long period grating (GO-dLPG) based immunosensor has been implemented for ultrasensitive detection of antibody/antigen interaction. The GO-LPG based biosensor has been developed for label-free haemoglobin detection. Apart from biosensors, the black phosphorus (BP) integrated tilted fibre grating (TFG) has been proposed, for the first time, as BP-fibre optic chemical sensor for heavy metal (Pb2+ ions) detection, demonstrating ultrahigh sensitivity, lower limit of detection and wider concentration range. Ultrafast laser micromachining technology has been employed to fabricate long period grating (LPG) and microstructures on optical fibre. The ultrafast laser micromachined polymer optical fibre Bragg grating (POFBG) has been developed for humidity sensing, showing the significant improvement with the reduced response time.
15
Cheshmehdoost, A. "High integrity bus structures for optical fibre sensors." Thesis, Brunel University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339305.
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Zhao, Weizhong. "Optical fibre high temperature sensors and their applications." Thesis, City University London, 2011. http://openaccess.city.ac.uk/1190/.
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Ioannides, Nicos. "Novel opto-electronic and plastic optical fibre sensors." Thesis, London Metropolitan University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287610.
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The design and performance of a novel displacement sensor is investigated both theoretically and experimentally. This is an optical, extrinsic and differential sensor based on the inverse square law and is insensitive to source intensity variations. It can, in principle, be implemented using only opto-electronic components or it can incorporate optical fibres to allow for EMI free and remote operation. The sensor is implemented using Plastic Optical Fibres (POF) as these offer considerable advantages over glass fibres or glass fibre bundles. The sensor head consists of three POFs positioned side by side and displaced from each other parallel to the axis of the sensor head by a separation X, (mm). The middle POF is coupled to a red LED and emits light onto a flat target with the two outer fibres receiving the reflected light from the target and guiding it to two silicon PIN photodiodes. Theoretical investigations on the behaviour of the sensor are presented for ranges between 0 mm and 100 mm, and for targets with different reflectivities. Non-linearities in the form of a spike are shown to exist in the very short ranges resulting in a minimum operational range of about 15 nun Beyond this minimum range the sensor response is linear and depends on the reflectivity of the target, the accuracy of calibration between the two detectors, any offset voltage present in any of the detectors, possible errors on the detected signals and the X, separation which in principle can be used to scale the sensor. Experimental results obtained confirm the long and linear operational range of the sensor (between 15 mm and 90 mm for a mirror target and between 20 mm and 100 mm for a matt white paper target). Likely variations in the source light intensity do not affect the performance and accuracy of the sensor. Measurements performed with various X, separations verify the scalability feature of the sensor in that by increasing X, one can achieve longer operational ranges. Temperature variations up to 40 °c do not affect the linearity of response. Effects arising from angular misalignment of the target and! or the ends of the three POFs are also investigated and could be minimised by rotating the emitting POF. Matt white paper is concluded as the preferred type of target since it offers a longer linear operational range with less stringent alignment requirements as opposed to reflective targets. Operation of the sensor under ambient illumination conditions is demonstrated using suitable electronic circuitry with filtering facilities. The result is a linear operational range of 60 mm with 1 % accuracy with a matt white paper target. An automated version of the sensor under software control is also demonstrated for monitoring large amplitude (0.15 mm - 6 mm), single degree vibrations. The maximum determined frequency of the vibrating surface is about 150 Hz and this is only limited by the target displacement which is close to the resolution limits of this version of the sensor (0.15 mm). This novel sensor offers considerable advantages over other sensors reported in the literature. It is shown to offer a very long and linear operational range in excess of 100 mm, with accuracy better than 1% and resolution better than 0.2 % of range, and currently this performance is only limited by the electronic circuitry used. Overall, the proposed sensor offers a superior sensor head arrangement and performance combination and its cost is expected to be very low. Suggestions for improvements and other applications are offered.
18
Gander, Matthew James. "Multicore optical fibre sensors for differential strain measurement." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/513.
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Edwards, Henry Owen. "A study of techniques for optical fibre sensors." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/399484/.
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This thesis reports on work performed within the field of optical fibre sensors. The topics studied cover three main areas of sensor research; fibre-remoted gas detection, the optical actuation of a resonant quartz device, and the assessment of compound glasses and fibres for current measurement applications. The gas detection techniques described have the common advantage of highly-selective measurement, and are applied to a number of industrial and environmental gases. Selectivity is achieved by effectively monitoring the spectral overlap between the gas sample to be measured, and that of a reference gas. Three techniques were employed to vary the spectral overlap, including Stark, pressure, and frequency modulation. For quantitative gas detection at atmospheric pressure, the modulation techniques are demonstrated here for the first time with fibre-remoted sampling cells. Practical examples of sensors for detection of methane, ammonia and carbon dioxide were demonstrated, and gas sensitivities down to 50ppm by volume were achieved. The optical powering and readout of a quartz resonator was demonstrated. An open-ended tuning fork device was used, and a novel interferometric technique was employed to minimise the optical drive power required. Threshold optical power levels of less than 25µW were achieved. The configuration was capable of operation with only a single fibre link to the sensor head, to carry both optical drive and readout signals, and a single optical source was employed. Optical fibre current monitors employing the Faraday effect can suffer measurement bandwidth restrictions if a long fibre is employed in order to attain good sensitivity. As the Faraday effect in many compound glasses is considerably stronger than for a standard silica fibre, then an equivalent sensitivity can be achieved for a shorter fibre coil by the use of compound glasses. The sensitivity and bandwidth of a typical current monitor configuration are analyzed for a number of compound glasses for the first time. The Verdet constant of a trial fibre fabricated from one promising compound glass was measured.
20
Jones, Steven Lee. "Single mode optical fibre bend loss modelling." Thesis, Manchester Metropolitan University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264454.
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Yu, Aihua. "Application of optical fibre Sagnac interferometers in optical modulators and sensors." Thesis, University of Essex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332807.
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Buggy, Stephen J. "Composite material process monitoring using optical fibre grating sensors." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/4035.
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In this thesis a long period grating (LPG) based sensor is investigated as a possible
alternative to current process monitoring sensors used in the manufacture of composites
to monitor cure. An LPG is demonstrated as a means of monitoring the cure of a UVcured
epoxy resin. The wavelength shift of the attenuation bands were measured during
the cure of the resin and compared with measurements made using a fibre optic Fresnel
based refractometer. The results showed a good correlation (6 x 10
-3
rius) and illustrate
the potential of the techniques for non-invasive composite material cure monitoring.
Alternative fibre grating methods; a chirped LPG sensor, an in-fire Mach-Zehnder
interferometer and a tilted fibre Bragg grating sensor, are also presented to demonstrate
the versatility of grating based sensors for flow, high sensitivity refractive index and
multi-parameter sensing, respectively. Demonstrations of LPG sensors in industrial
applications are also presented and highlight the technical issues of integrating such
devices in composite components and composite manufacturing processes.
23
Topliss, Stephen M. "Optical fibre long period grating sensors with nanostructured coatings." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/6799.
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The dual resonant response of long period fibre gratings (LPG) operating near the phase matching turning point to the deposition of nanostructured coatings is explored. A broad range of LPGs have been fabricated with grating periods ranging from 80m to 180m, and these have been characterized with three different coating materials,-tricosensoic acid, undecyl-calix[4]resorcarene and tert-butyl-calix[8]arene carboxylic acid. The dual resonant response has been exploited with the construction of an LPG based sensor coated with a quinolinium dye forming a pH sensor. The wavelength response of this device was measured with a sensitivity of -0.55pH/nm.
Furthermore, length apodised phase shifted long period gratings have been characterized, and the effect on the dual resonant response has been recorded. Partial coating of this device has resulted in the observation of a bandgap feature in the wavelength response.
The use of calixarenes as a functional coating for long period fibre gratings is also investigated. Calixarene is applied in a thin layer with a thickness of several hundred nm’s to the cladding of the fibre in the region containing the LPG sensor. The chemical sensing capabilities of a long period fibre grating sensor is presented for the detection of the volatile organic compounds; hexane, cyclohexane, benzene and toluene. The wavelength response was measured and the sensitivity to toluene vapour was recorded at 1600ppmv/nm. Using intensity detection of the central maxima in the wavelength response, the chemical selectivity is demonstrated showing sensitivity to toluene vapour over 13 times greater compared to hexane vapour.
24
Silva-Lopez, Manuel. "Optical fibre sensors for transverse strain and bend measurement." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/110.
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Isaac, Leslie Thomas. "Puffer circuit breaker diagnostics using novel optical fibre sensors." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263762.
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Khandaker, Iman Ibrahim. "Optical fibre sensors for the optimization of plasma processing." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318236.
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Wilson, Alan. "Interrogation techniques for short gauge length optical fibre sensors." Thesis, Cranfield University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266987.
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Bey, Samer Abi Kaed. "Development of paired long period grating optical fibre sensors." Thesis, City University London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514498.
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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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Al-Raweshidy, Hamed S. "Spread spectrum multiplexing for passive optical fibre interferometric sensors." Thesis, University of Strathclyde, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.703110.
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Hernandez, Ledezma Francisco Ulises. "Optical fibre sensors for novel medical devices during anaesthesia." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50339/.
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This research focuses on the development of optical fibre sensors that can be applied during critical care. The sensors developed are: (i) an optical fibre humidity sensor based on the deposition of a hygroscopic film onto the distal tip of the fibre and forming a Fabry-Pêrot cavity; (ii) chemical functionalization of U-shaped fibres and Long Period Gratings (LPGs). Fibre Bragg Gratings (FBGs) are only used for temperature monitoring in this work. The current trends in a new generation of humidity sensors suggest that electronic-based technologies could be soon replaced by photonic sensors due to better response times. Optical fibre technology has been considered as a promising platform for providing engineering solutions to unmet clinical needs. For example, anaesthetized patients are transferred from the induction room to the MRI room and taken back, with the need for continuous monitoring of vital signs such as respiration, but some technologies lack compatibility with MRI fields. In the operating room, patients are under anaesthesia, intubated and mechanically ventilated, but some under-humidification or over-humidification of the ventilation air causes secondary effects. Anaesthesiologists rely on total intravenous anaesthesia (TIVA) and monitoring of vital signs as indicators of unconsciousness; current investigations have shown that there is a need to measure the concentration of propofol in real time directly from the blood or breath of patients. Similarly, patients in the intensive care unit (ICU) after surgery require continuous monitoring of diverse biochemical parameters. In this research, the application of optical fibre sensors is demonstrated as an engineering solution for some of these clinical challenges. The simultaneous measurement of humidity and temperature with an optical fibre sensor, a biosensor for propofol detection and another for protein detection were fabricated and demonstrated in this work. The sensitivity, response time and hysteresis of a novel optical fibre humidity sensor has been investigated over a humidity range of 5% Relative Humidity (RH) to 95% RH using a controlled bench-top set-up. The optical fibre humidity sensor proposed has a very simple and low cost porous structured sensing element obtained with poly(allylamine hydrochloride) (PAH) and silica (SiO2) using the layer-by-layer (LbL) fabrication method. The fast response of the sensor (1.13 ± 0.3 s) enabled changes in humidity in individual breaths to be resolved. After calibration, the performance of the sensor was evaluated in the breathing circuit of a mechanical ventilator and respiratory equipment where its faster response allowed monitoring of breath to breath humidity levels during different modes of ventilation. It also has the capability to provide absolute humidity (AH) measurements when an FBG is included for simultaneous temperature measurements. An LPG sensor anchored with SiO2 core and gold (Au) shell nanoparticles has been investigated as a biosensing platform for protein detection. The well-known protein interaction between biotin and streptavidin (SV) was used as a proof of concept. The proposed sensor presented Langmuir adsorption to SV concentrations with a limit of detection (LoD) down to 15.13 nM and a lowest detected concentration of 2.5 nM. In addition, U-shaped fibres and LPGs functionalized with host-guest imprinted TiO2 thin films were used to test propofol detection in aqueous solutions. These sensors also presented Langmuir adsorption in the mili-molar range in aqueous solutions and a lowest detected concentration of 0.65 uM. Detection limits of propofol were improved with the addition of mesoporous silica nanoparticles (MSNs) and inorganic molecular imprinting to allow detection down to 99 nM in aqueous solution and 30 ppb in gaseous phase. In conclusion, this research has successfully demonstrated the use of novel optical fibre sensors in laboratory and real conditions through embedding the developed sensors in critical care equipment usually used during anaesthesia.
32
Berwick, M. "Investigations toward Faraday effect optical current sensors and optical fibre frequency shifters." Thesis, University of Kent, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290423.
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Yakum, Charles Nchonko. "Electric current measurement in power systems using optical fibre techniques." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387450.
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McKenzie, James Stuart. "Optical actuation and control-by-light systems." Thesis, Brunel University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286728.
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Luke, David George. "Broadband optical fibre interferometry for strain measurement in composite materials." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/655.
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Wang, Qi. "Studies of multimode fibre linked white light interferometric sensor systems." Thesis, City University London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389649.
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Nair, Abilash Kumar Kochumulappon Raghavan. "Process and structural health monitoring of advanced fibre reinforced composites using optical fibre sensors." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5662/.
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The focus of this research was to design, optimise and deploy a practical multi-measurand sensor (MMS) for process monitoring of glass and carbon fibre preforms in an autoclave. The MMS design was based on the optical fibre-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor. The EFPI sensor consisted of a pair of cleaved optical fibres, with a defined gap that were housed in a precision bore capillary. Interferometric interrogation was used to measure the cavity length hence, permitting the strain to be determined. The basic EFPI sensor design was modified in the following manner to enable multi-measurand monitoring. Firstly, a fibre Bragg grating (FBG) was inscribed on one of the optical fibres that were destined to be housed in the capillary; the end-face of this cleaved optical fibre was sputter coated with Au/Pd to produce a reflective surface. This FBG is in a relatively strain-free condition and only responds to temperature. Secondly, a technique was developed to manufacture optical-quality end-faces of the capillary and this too was sputter coated with Au/Pd. Thirdly, secondary cleaved optical fibres were packed around the lead-in optical fibre of the EFPI sensor with a defined (secondary) cavity thus, permitting transmission/reflection FTNIR spectroscopy. Finally, cleaved secondary optical fibres were also secured to the lead-in fibre and these served as Fresnel reflection sensors. The interrogation of the MMS was carried out using a conventional fibre-coupled multi-channel FTNIR spectrometer. The feasibility of monitoring strain, temperature, cross-linking kinetics and refractive index simultaneously during the processing of glass and carbon fibre preforms was demonstrated.
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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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Hayward, Justin Peter William. "Distributed optical-fibre sensors for monitoring mechanical strain and disturbance." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/46856/.
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This thesis reports work carried out to develop an optical sensor capable of detecting disturbance of optical fibre cables, for application in protection of telecommunications infrastructure. Initially, three types of sensor were investigated, however after preliminary experimental and theoretical work it was decided to concentrate on a novel coherent-optical time-domain reflectometer (C-OTDR). The operation of the C-OTDR has been investigated theoretically, using various models to describe coherent scattering in the optical fibre. The assumptions used in the models were applied to a numerical simulation of coherent scattering, obtaining results in good agreement with theoretical predictions and experimental measurements. Having developed a clear explanation of the sensor's operation, a detailed noise analysis is carried out, enabling the limiting factors to be identified and minimised. The design and development of a portable sensor system is then described, and the results from a number of field trials are presented. Seeking to explain unexpected observations during these trials, a detailed experimental and theoretical analysis of the limits due to optical non-linearity was carried out, showing that the pulse power is limited by the need to prevent spectral broadening due to self-phase modulation, which adds noise to the sensor output. Applying the findings of these investigations, further field trials and laboratory tests were carried out with improved experimental C-OTDR sensors. By optimising the pulse power and carefully controlling the noise sources, it has been possible to demonstrate operation at longer ranges, with superior spatial resolution, than has been reported for other sensors of this type.
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Davies, Edward. "Optical fibre sensors with applications in gas and biological sensing." Thesis, Aston University, 2011. http://publications.aston.ac.uk/15800/.
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This thesis describes the study of various grating based optical fibre sensors for applications in refractive index sensing. The sensitivity of these sensors has been studied and in some cases enhanced using novel techniques. The major areas of development are as follows. The sensitivity of long period gratings (LPGs) to surrounding medium refractive index (SRI) for various periods was investigated. The most sensitive period of LPG was found to be around 160 µm and this was due to the core mode coupling to a single cladding mode but phase matching at two wavelength locations, creating two attenuation peaks, close to the waveguide dispersion turning point. Large angle tilted fibre gratings (TFGs) have similar behaviour to LPGs, in that they couple to the co-propagating cladding modes. The tilted structure of the index modulation within the core of the fibre gives rise to a polarisation dependency, differing the large angle TFG from a LPG. Since the large angle TFG couple to the cladding mode they are SRI sensitive, the sensitivity to SRI can be further increased through cladding etching using HF acid. The thinning of the cladding layer caused a reordering of the cladding modes and shifted to more SRI sensitive cladding modes as the investigation discovered. In a SRI range of 1.36 to 1.40 a sensitivity of 506.9 nm/URI was achieved for the etched large angle TFG, which is greater than the dual resonance LPG. UV inscribed LPGs were coated with sol-gel materials with high RIs. The high RI of the coating caused an increase in cladding mode effective index which in turn caused an increase in the LPG sensitivity to SRI. LPGs of various periods of LPG were coated with sol-gel TiO2 and the optimal thickness was found to vary for each period. By coating of the already highly SRI sensitive 160µm period LPG (which is a dual resonance) with a sol-gel TiO2, the SRI sensitivity was further increased with a peak value of 1458 nm/URI, which was an almost 3 fold increase compared to the uncoated LPG. LPGs were also inscribed using a femtosecond laser which produced a highly focused index change which was no uniform throughout the core of the optical fibre. The inscription technique gave rise to a large polarisation sensitivity and the ability to couple to multiple azimuthal cladding mode sets, not seen with uniform UV inscribed gratings. Through coupling of the core mode to multiple sets of cladding modes, attenuation peaks with opposite wavelength shifts for increasing SRI was observed. Through combining this opposite wavelength shifts, a SRI sensitivity was achieved greater than any single observed attenuations peak. The maximum SRI achieved was 1680 nm/URI for a femtosecond inscribed LPG of period 400 µm. Three different types of surface plasmon resonance (SPR) sensors with a multilayer metal top coating were investigated in D shape optical fibre. The sensors could be separated into two types, utilized a pre UV inscribed tilted Bragg grating and the other employed a post UV exposure to generate surface relief grating structure. This surface perturbation aided the out coupling of light from the core but also changed the sensing mechanism from SPR to localised surface plasmon resonance (LSPR). This greatly increased the SRI sensitivity, compared to the SPR sensors; with the gold coated top layer surface relief sensor producing the largest SRI sensitivity of 2111.5nm/URI was achieved. While, the platinum and silver coated top layer surface relief sensors also gave high SRI sensitivities but also the ability to produce resonances in air (not previously seen with the SPR sensors). These properties were employed in two applications. The silver and platinum surface relief devices were used as gas sensors and were shown to be capable of detecting the minute RI change of different gases. The calculated maximum sensitivities produced were 1882.1dB/URI and 1493.5nm/URI for silver and platinum, respectively. Using a DFB laser and power meter a cheap alternative approach was investigated which showed the ability of the sensors to distinguish between different gases and flow rates of those gases. The gold surface relief sensor was coated in a with a bio compound called an aptamer and it was able to detect various concentrations of a biological compound called Thrombin, ranging from 1mM to as low as 10fM. A solution of 2M NaCl was found to give the best stripping results for Thrombin from the aptamer and showed the reusability of the sensor. The association and disassociation constants were calculated to be 1.0638×106Ms-1 and 0.2482s-1, respectively, showing the high affinity of the Aptamer to thrombin. This supports existing working stating that aptamers could be alternative to enzymes for chemical detection and also helps to explain the low detection limit of the gold surface relief sensor.
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Pappu, Raja. "Acoustic emission detection using optical fibre sensors for aerospace applications." Thesis, Aston University, 2012. http://publications.aston.ac.uk/19136/.
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Structural Health Monitoring (SHM) ensures the structural health and safety of critical structures covering a wide range of application areas. This thesis presents novel, low-cost and good-performance fibre Bragg grating (FBG) based systems for detection of Acoustic Emission (AE) in aircraft structures, which is a part of SHM. Importantly a key aim, during the design of these systems, was to produce systems that were sufficiently small to install in an aircraft for lifetime monitoring. Two important techniques for monitoring high frequency AE that were developed as a part of this research were, Quadrature recombination technique and Active tracking technique. Active tracking technique was used extensively and was further developed to overcome the limitations that were observed while testing it at several test facilities and with different optical fibre sensors. This system was able to eliminate any low frequency spectrum shift due to environmental perturbation and keeps the sensor always working at optimum operation point. This is highly desirable in harsh industrial and operationally active environments. Experimental work carried out in the laboratory has proved that such systems can be used for high frequency detection and have capability to detect up to 600 kHz. However, the range of frequency depends upon the requirement and design of the interrogation system as the system can be altered accordingly for different applications. Several optical fibre configurations for wavelength detection were designed during the course of this work along with industrial partners. Fibre Bragg grating Fabry-Perot (FBG-FP) sensors have shown higher sensitivity and usability than the uniform FBGs to be used with such system. This was shown experimentally. The author is certain that further research will lead to development of a commercially marketable product and the use of active tracking systems can be extended in areas of healthcare, civil infrastructure monitoring etc. where it can be deployed. Finally, the AE detection system has been developed to aerospace requirements and was tested at NDT & Testing Technology test facility based at Airbus, Filton, UK on A350 testing panels.
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Hodgkinson, Jane. "Photoacoustic and photothermal detection of trace compounds in water." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244982.
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Sohlström, Hans. "Fibre Optic Magnetic Field Sensors Utilizing Iron Garnet Materials." Doctoral thesis, KTH, Signaler, sensorer och system, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48332.
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This thesis deals with the subject of fibre optic magnetic field sensors utilizing iron garnet materials. Such materials exhibit a large Faraday rotation which make them advantageous for application in compact magnetic field sensors. After an introduction, in which fibre optic sensors and optical methods to measure electric current are reviewed, the original research work is summarized. A system for the measurement of the magneto-optic properties of transparent materials is described. Measurement results, showing the influence of temperature, magnetic field direction and sample treatment on the magneto-optical properties of YIG-crystals, are presented. The properties of thin magneto-optical waveguiding films have also been studied using different light coupling methods. Measurement results obtained for holographic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. It is shown that the launching method may affect the properties to be measured. The design and performance of several versions of extrinsic guided wave fibre optic magnetic field sensors are then reported. The sensors employ substituted YIG (Yttrium Iron Garnet, Y3Fe5O12) thin film waveguides as sensing elements. Polarization maintaining fibres were used as feed and return to provide two signal channels. The signals were combined in a balanced measurement system, providing insensitivity to both fluctuations in optical power and loss. Sensors have been made both with separate fibres to guide the light to and from the sensing element and with a single fibre for both functions. The two fibre version, although less ”elegant”, is found to have a better performance. This version also makes it possible to determine both the magnitude and sign of the magnetic field. Measurement results indicate a usable measurement range of at least several mT with a noise equivalent magnetic field level of less than 8 nT/root(Hz). The design and performance of multimode fibre optic magnetic field sensors utilizing the Faraday effect in an epitaxially grown thick (YbTbBi)IG film is also described. This type of sensor is found to be linear over a range from 27 mT to less than 270 nT. Sensor prototypes suitable for current monitoring in high voltage transmission lines have also been developed.QC 20111209
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Hayes, Simon Antony. "Development of a reinforcing fibre light-guide for use as a damage sensor within composite structures." Thesis, Brunel University, 1995. http://bura.brunel.ac.uk/handle/2438/7119.
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This study presents the results of an investigation to develop a novel sensor which would give a direct indication of the extent of impact damage in a composite. This was achieved by using glass reinforcing fibres to produce a light-guide, which was embedded within a composite laminate. The laminate was then subjected to impact events or bending stresses of sufficient magnitude to cause damage. The impact energies used in this study varied between 2 and 10 Joules, and the indentation depths varied between 0.125 and 1 mm, allowing damage propagation to be monitored. The fall-off in the transmitted light was used to monitor the level of damage, along with C-scanning and sectioning to provide reference data. The use of reinforcing fibres to produce the sensor meant that the strains required to cause failure in the fibres was realistically close to those of the composite constituents. Changes in the transmission characteristics of the sensor were found to correspond to real failure events occurring during impact.
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Hua, Yan. "Development of photonic-based measurement devices." Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308172.
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Zheng, Gang. "Development of advanced birefringent fibre force sensor systems based on frequency modulation continuous wave (FMCW) technology." Thesis, Glasgow Caledonian University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337411.
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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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Yang, Yatao. "Development of a distributed optical fibre pH sensor system." Thesis, Glasgow Caledonian University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321322.
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Beeby, Stephen Paul. "Mechanical isolation of miniature resonant sensors and stress relieving packages." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242715.
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Allwood, Gary Andrew. "Intensity based interrogation of optical fibre sensors for industrial automation and intrusion detection systems." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2015. https://ro.ecu.edu.au/theses/1702.
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In this study, the use of optical fibre sensors for intrusion detection and industrial automation systems has been demonstrated, with a particular focus on low cost, intensity-based, interrogation techniques. The use of optical fibre sensors for intrusion detection systems to secure residential, commercial, and industrial premises against potential security breaches has been extensively reviewed in this thesis. Fibre Bragg grating (FBG) sensing is one form of optical fibre sensing that has been underutilised in applications such as in-ground, in-fence, and window and door monitoring, and addressing that opportunity has been a major goal of this thesis. Both security and industrial sensor systems must include some centralised intelligence (electronic controller) and ideally both automation and security sensor systems would be controlled and monitored by the same centralised system. Optical fibre sensor systems that could be used for either application have been designed, developed, and tested in this study, and optoelectronic interfaces for integrating these sensors with electronic controllers have been demonstrated. The versatility of FBG sensors means that they are also ideal for certain mainstream industrial applications.
Two novel transducers have been developed in this work; a highly sensitive low pressure FBG diaphragm transducer and a FBG load cell transducer. Both have been designed to allow interrogation of the optical signal could occur within the housing of the individual sensors themselves. This is achieved in a simple and low cost manner that enables the output of the transducers to be easily connected to standard electronic controllers, such as programmable logic controllers. Furthermore, some of the nonlinear characteristics of FBG sensors have been explored with the aim of developing transducers that are inherently decoupled from strain and temperature interference. One of the major advantages of optical fibre sensors is their ability to be both time division and wavelength division multiplexed. The intensity-based interrogation techniques used here complement this attribute and are a major consideration when developing the transducers and optoelectronic circuits. A time division multiplexing technique, using transmit-reflect detection and incorporating a dual bus, has also been developed. This system architecture enables all the different optical fibre transducers on the network to have the same Bragg wavelength and hence the number of spare replacement transducers required is minimal. Moreover, sensors can be replaced in an online control system without disrupting the network. In addition, by analysing both the transmitted and reflected signals, problems associated with optical power fluctuations are eliminated and the intensity of the sensor signals is increased through differential amplification.
Overall, the research addresses the limitations of conventional electrical sensors, such as susceptibility to corrosive damage in wet and corrosive environments, and risk of causing an explosion in hazardous environments, as well as the limitations of current stand-alone optical fibre sensor systems. This thesis supports more alert, reliable, affordable, and coordinated, control and monitoring systems in an on-line environment.