CERES :: Browsing by Author "James, Stephen W."

Browsing by Author "James, Stephen W."

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Open Access
Advanced fibre optic long period grating sensors; design, fabrication and sensing
(Cranfield University, 2014-05) Wong, Rebecca; James, Stephen W.; Tatam, Ralph P.
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.
Open Access
AFM observation of surface topography of fibre Bragg gratings fabricated in germanium-boron codoped fibres and hydrogen-loaded fibres.
(Elsevier Science B.V., Amsterdam., 2002-11-01T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Irving, Phil E.; Tatam, Ralph P.
This paper reports the measurement of the surface topology of optical fibres containing a fibre Bragg grating (FBG) using an atomic force microscope (AFM). The AFM observation was made on FBGs fabricated via the phase mask technique in germanium–boron codoped optical fibres, in hydrogen-loaded germanium–boron codoped fibres and in standard telecommunications optical fibres. The surface images reveal that a spatial corrugation pattern was induced by the UV- irradiation, with a period that is half of the period of the phase mask. This UV-induced surface structure was found only on the side of the fibre facing towards the incident UV-irradiation and did not appear on the rear surface. The AFM probe scanned a 10×10 μm2 surface area at seven sites along the 6.0 mm length of fibre that was exposed to the UV-irradiation. The amplitude of the spatial corrugation pattern observed on the AFM image was quantified for each site. It was found that the amplitude in a range of 0.7–3.2 nm was a function of UV-laser intensity distribution and the type of fibre. Hydrogen loaded optical fibres exhibited a corrugation with an amplitude twice as large as that observed in the Ge–B doped fibres that were not hydrogen-loaded. This correlates with the increase in photosensitivity produced by the hydrogen loading. A similar UV- induced spatial corrugation was also observed on standard telecom fibres, but without inducing the refractive index change in the fibre core. The observation of surface topology provides an insight into the structural changes induced during FBG fabrication. UV-induced densification and laser ablation could account for the formation of the surfac
Open Access
Ammonia sensing using lossy mode resonances in a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
(Society of Photo-optical Instrumentation Engineers (SPIE), 2016-05-30) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
The development of an ammonia sensor, formed by the deposition of a functionalised titanium dioxide film onto a tapered optical fibre is presented. The titanium dioxide coating allows the coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating lossy mode resonance (LMR) in the transmission spectrum. The porphyrin compound that was used to functionalise the coating was removed from the titanium dioxide coating upon exposure to ammonia, causing a change in the refractive index of the coating and a concomitant shift in the central wavelength of the lossy mode resonance. Concentrations of ammonia as small as 1ppm was detected with a response time of less than 1min. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Open Access
An ammonia sensor based on Lossy Mode Resonances on a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
(Elsevier, 2017-04) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
The development of a highly sensitive ammonia sensor is described. The sensor is formed by deposition of a nanoscale coating of titanium dioxide, containing a porphyrin as a functional material, onto a tapered optical fibre. The titanium dioxide coating allows coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating a Lossy Mode Resonance (LMR) in the transmission spectrum. A change in the refractive index of the coating caused by the interaction of the porphyrin with ammonia causes a change in the centre wavelength of the LMR, allowing concentrations of ammonia in water as low as 0.1 ppm to be detected, with a response time of less than 30 s.
Open Access
Automated manufacture of 3D reinforced aerospace composite structures
(2012-03-05T00:00:00Z) Dell'Anno, Giuseppe; Partridge, Ivana K.; Cartié, Denis D. R.; Hamlyn, A.; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.
Purpose- This study is part of the FP7 project ADVITAC and focuses on exploring an innovative combination of cutting edge technologies to be implemented within automated processes for composite parts manufacturing. The objective is the design of a production route for components with tailored fibre orientation and ply lay-up, with improved damage tolerance thanks to through-the-thickness reinforcement and integrated health monitoring systems based on optical fibres technology. Design/Methodology/Approach- The proposed technologies are described in detail and their compatibility and potential for integration are discussed. A set up for on-line monitoring of infusion and curing processes of carbon/epoxy laminates preformed by dry fibre placement technology is proposed, and a preliminary study of their mechanical performance is presented. The possibility of reinforcing through-the-thickness preforms manufactured with dry slit tapes automatically laid-up and consolidated by laser heating is investigated. Findings- Improved knowledge of interaction/compatibility between the discussed technologies and scope for application. Research limitations/implications- The paper reports the technical potential and practical feasibility of the proposed integrated production process. Limited quantitative evaluations on the materials performance are provided. The analysis of the technologies involved represents the early outcome of the ongoing ADVITAC project. Practical implications- This study contributes to the identification of a new generation of composite architecture which allows production cost and weight savings while retaining the level of quality suitable for demanding structural applications, with particular relevance to the aerospace field. Originality/value- This paper investigates for the first time the practical possibility of designing a single automated process involving dry fibre placement, tufting and optical fibre sensor monitoring for the production of complex composite components.
Open Access
Characterisation of a cryostat using simultaneous, single-beam multiple-surface laser vibrometry
(American Institute of Physics Publishing, 2016-06-28) Kissinger, Thomas; Charrett, Thomas O. H.; James, Stephen W.; Adams, Alvin; Twin, Andrew; Tatam, Ralph P.
A novel range-resolved interferometric signal processing technique that uses sinusoidal optical frequency modulation is applied to multi-surface vibrometry, demonstrating simultaneous optical measurements of vibrations on two surfaces using a single, collimated laser beam, with a minimum permissible distance of 3.5 cm between surfaces. The current system, using a cost-effective laser diode and a fibre-coupled, downlead insensitive setup, allows an interferometric fringe rate of up to 180 kHz to be resolved with typical displacement noise levels of 8 pm · Hz−0 5. In this paper, the system is applied to vibrometry measurements of a table-top cryostat, with concurrent measurements of the optical widow and the sample holder target inside. This allows the separation of common-mode vibrations of the whole cryostat from differential vibrations between the window and the target, allowing any resonances to be identified.
Open Access
Characterization of the response of fibre Bragg gratings fabricated in stress and geometrically induced high birefringence fibres to temperature and transverse load.
(Institute of Physics, 2004-08-01T00:00:00Z) Chehura, Edmon; Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.
The transverse load and temperature sensitivities of fibre Bragg gratings (FBGs) fabricated in a range of commercially available stress and geometrically induced high birefringent (HiBi) fibres have been experimentally investigated. The wavelength reflected by the FBG in each polarization eigenmode was measured independently and simultaneously using a custom designed interrogation system. The highest transverse load sensitivity, of 0.23 ± 0.02 nm/(N/mm), was obtained with HiBi FBGs fabricated in elliptically clad fibre. This was higher than for any other HiBi fibre, which, coupled with the small diameter of the fibre, makes it a good candidate for an embedded or surface mounted strain sensor. The highest temperature sensitivity of 16.5 ± 0.1 pm °C-1, approximately 27% greater than any other fibre type, was obtained with the HiBi FBG fabricated in Panda fibre. HiBi FBG sensors fabricated in D-clad fibre were the only ones to exhibit identical temperature sensitivities for the slow and fast axes (11.5 ± 0.1 pm °
Open Access
Combined shearography and speckle pattern photography for single-access multi- component surface strain measurement
(International Society for Optical Engineering; 1999, 2003-12-31T00:00:00Z) Groves, Roger M.; James, Stephen W.; Tatam, Ralph P.; Fu, S.; Shen, Gongxin X.; Cha, Soyoung S.; Chiang, F. P.; Mercer, Carolyn R.
Full surface strain measurement requires the determination of two out-of-plane and four in-plane displacement gradient components of the surface strain tensor. Shearography is a full-field speckle interferometry technique with a sensitivity predominately to the out-of-plane displacement gradient. Speckle pattern photography has the sensitivity to the in-plane displacement, and taking the derivative yields the in-plane displacement gradient. In this paper the two techniques are combined to yield a single-access multi-component surface strain measurement using shearography to measure the out-of-plane components and speckle pattern photography to measure the in-plane components. Results are presented of a multi-component surface strain measurement.
Open Access
Composite material process monitoring using optical fibre grating sensors
(Cranfield University, 2008-06) Buggy, Stephen J.; Tatam, Ralph P.; James, Stephen W.
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.
Open Access
Cost-effective vibration and displacement measurement using range-resolved interferometry
(British Society for Strain Measurement’s (BSSM), 2015-09-03) Kissinger, Thomas; Charrett, Thomas O. H.; James, Stephen W.; Tatam, Ralph P.
A recently developed range-resolved optical interferometric signal processing technique is applied to vibration and displacement sensing with fibre-based beam delivery. The technique is demonstrated to allow the simultaneous acquisition of high-quality, high resolution relative displacement measurements (ߪ ൌ ͵ ) based on interferometric phase evaluation along with coarser ሺߪ ൌ ͲǤͲͷ ) absolute displacement measurements. The interferometric relative displacement data can be used for vibrometry measurement and to yield high-quality derivative velocity and acceleration data suitable for position control applications. The absolute data can serve as an additional proximity sensor. The sensing approach employs cost-effective diode lasers, off-the-shelf digital processing hardware and a very simple optical setup, and can, due to the use of a collimated beam, operate over a wide range of working distances.
Open Access
Cryogenic Temperature Response Of Fibre Optic Long Period Gratings.
(Iop Publishing Ltd, 2003-08-01T00:00:00Z) James, Stephen W.; Tatam, Ralph P.; Twin, Andrew; Bateman, Rod; Noonan, Paul
The thermal response of the attenuation bands of an optical fibre long period grating was monitored over a temperature range of 4.2–280 K. A linear dependence of the central wavelength of the band, of gradient 0.2 nm K-1, was observed over the range 77–280 K. A measurable wavelength shift was observed at temperatures as low as 20 K.
Open Access
Cure monitoring of a UV cured epoxy resin using a long period grating Mach- Zehnder interferometer
(International Society for Optical Engineering; 1999, 2007-12-31T00:00:00Z) Buggy, Stephen J.; Murphy, Richard P.; James, Stephen W.; Tatam, Ralph P.; Cutolo, A.; Culshaw, B.; Lpez-Higuera, J. M.
A cascaded long period grating Mach-Zehnder interferometer is used to monitor the change in refractive index of a UV cured epoxy resin over a cure cycle. Fourier techniques are used to calculate the phase shift and frequency spectral amplitude of the associated fringe pattern during the cure. The results are compared with the refractive index change during cure calculated using a Fresnel reflection based technique.
Open Access
Demodulation and de-multiplexing of a fibre Bragg grating sensor array using volume holograms
(Cranfield University, 2009) Reeves, Richard John; James, Stephen W.; Tatam, Ralph P.
The demodulation of a Wavelength Division Multiplexed FBG sensor array by a matching array of holograms hosted within a Volume Holographic (VH) material is considered within this thesis. The FBG sensor elements possess separate quiescent wavelengths and operate within different wavelength ranges. The edge of the transfer function of the demodulating holographic element is aligned with the operating range of the matching sensor element. The holographic element then diffracts a fraction of the sensor signal depending on its instantaneous wavelength. The signals from each of the sensor elements are also diffracted through separate angles to matching detectors so de-multiplexing the sensor array. A scheme using narrow bandwidth holographic transfer functions to demodulate a two element strain sensor array fabricated 4nm apart is reported. The transfer functions and the hysteresis within the PZT actuator, applying the strain, are represented mathematically and used to process results. These are compared with a normalised saw-tooth voltage waveform applied to the PZT to achieve a high Pearson correlation factor of 0.9992. The holograms however possessed poor diffraction efficiency <1% so severely degrading strain resolution. The crosstalk between the sensors’ channels is measured as -8.3dB. The demodulation scheme is intensity based so is susceptible to fluctuations in source intensity and fibre bend losses. An intensity reference scheme is therefore demonstrated using two holograms to demodulate a single FBG strain sensor. The sensor’s signal is divided by the two holograms and the intensity of the respective parts recorded on matched photo-detectors. Ratiometric detection is then used to identify changes in applied strain while disregarding fluctuations in source intensity and fibre bend losses. The standard difference over sum equation for ratiometric detection however is modified to take account of the respective holographic transfer functions.
Open Access
Design and fabrication of optical fibre long period gratings for CO₂ sensing
(2018-06) Barrington, James; James, Stephen W.; Partridge, Matthew; Tatam, Ralph P.
This thesis investigated the repeatability of the overwrite long period grating (LPG) fabrication method and highlighted the advantage it offers in its ability to tune spectral features thus allowing the manufacture of bespoke sensors. Moreover, LPGs with periods ranging from 100 - 200 μm were written and a novel technique for mapping the transmission data was presented. This method gave a unique overview into the period mediated evolution of attenuation features, which, when designing LPGs that operate at the sensitive phase matching turning point, is invaluable. Further exploration into the overwrite method revealed that the UV irradiation duty cycle used in the fabrication of LPGs was found to influence the presence of harmonics, where a duty cycle of 25% maximised coupling to 2nd order transmission features. LPGs which possessed these additional spectral features within a small wavelength range (600 - 1000 nm) were assessed for their suitability in performing multi-parameter sensing. Ionic liquids were explored as an LPG COThis thesis investigated the repeatability of the overwrite long period grating (LPG) fabrication method and highlighted the advantage it offers in its ability to tune spectral features thus allowing the manufacture of bespoke sensors. Moreover, LPGs with periods ranging from 100 - 200 μm were written and a novel technique for mapping the transmission data was presented. This method gave a unique overview into the period mediated evolution of attenuation features, which, when designing LPGs that operate at the sensitive phase matching turning point, is invaluable. Further exploration into the overwrite method revealed that the UV irradiation duty cycle used in the fabrication of LPGs was found to influence the presence of harmonics, where a duty cycle of 25% maximised coupling to 2nd order transmission features. LPGs which possessed these additional spectral features within a small wavelength range (600 - 1000 nm) were assessed for their suitability in performing multi-parameter sensing. Ionic liquids were explored as an LPG COThis thesis investigated the repeatability of the overwrite long period grating (LPG) fabrication method and highlighted the advantage it offers in its ability to tune spectral features thus allowing the manufacture of bespoke sensors. Moreover, LPGs with periods ranging from 100 - 200 μm were written and a novel technique for mapping the transmission data was presented. This method gave a unique overview into the period mediated evolution of attenuation features, which, when designing LPGs that operate at the sensitive phase matching turning point, is invaluable. Further exploration into the overwrite method revealed that the UV irradiation duty cycle used in the fabrication of LPGs was found to influence the presence of harmonics, where a duty cycle of 25% maximised coupling to 2nd order transmission features. LPGs which possessed these additional spectral features within a small wavelength range (600 - 1000 nm) were assessed for their suitability in performing multi-parameter sensing. Ionic liquids were explored as an LPG CO₂ sensitive coating. It was shown that these materials demonstrate a refractive index change upon exposure to CO₂ which was maintained following mechanical stabilisation using a gelling agent. A coating system for applying the gelled ionic liquid to the surface of an optical fibre was developed and techniques to improve the coating deposition were explored. The sensor demonstrated an 8 nm wavelength shift in response to 20% CO₂, which was reversible by reducing the partial pressure of CO₂ for 25 min.sensitive coating. It was shown that these materials demonstrate a refractive index change upon exposure to CO₂ which was maintained following mechanical stabilisation using a gelling agent. A coating system for applying the gelled ionic liquid to the surface of an optical fibre was developed and techniques to improve the coating deposition were explored. The sensor demonstrated an 8 nm wavelength shift in response to 20% CO₂, which was reversible by reducing the partial pressure of CO₂ for 25 min. sensitive coating. It was shown that these materials demonstrate a refractive index change upon exposure to CO₂ which was maintained following mechanical stabilisation using a gelling agent. A coating system for applying the gelled ionic liquid to the surface of an optical fibre was developed and techniques to improve the coating deposition were explored. The sensor demonstrated an 8 nm wavelength shift in response to 20% CO₂, which was reversible by reducing the partial pressure of CO₂ for 25 min.
Open Access
Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications
(American Institute of Physics, 1997-12-31T00:00:00Z) James, Stephen W.; Tatam, Ralph P.; Elder, R. L.
Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. The f/4 probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications.
Open Access
Detection of volatile organic compounds (VOCs) using an optical fibre long period grating with a calixarene anchored mesoporous thin film
(SPIE, 2013-05-06) Korposh, Sergiy; Davis, Frank; James, Stephen W.; Wang, T.; Lee, Seung-Woo; Higson, Seamus P. J.; Tatam, Ralph P.
A long period grating (LPG) modified with a mesoporous film infused with a functional compound, calix[4]arene, was employed for the detection of volatile organic compounds (VOCs). The mesoporous film consisted of an inorganic part, of SiO2 nanoparticles (NPs) along with an organic moiety of poly(allylamine hydrochloride) polycation PAH, which was finally infused with functional compound, p-sulphanatocalix[4]arene (CA[4]). The LPG sensor was designed to operate at the phase matching turning point to provide the highest sensitivity. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the complexion of the VOCs with calix[4]arene (CA). The LPG modified with 5 cycles of (SiO2 NPs/PAH)5PAA responded to exposure to chloroform and benzene vapours. The sensitivity to humidity as an interfering parameter was also investigated.
Open Access
Developing a proof of principle 3D-printed lab-on-a-disc assay platform.
(2017-05) Tothill, Alexander M.; James, Stephen W.; Partridge, Matthew; Tatam, Ralph P.
A 3D-printed microfluidic lab-on-a-disc (LOAD) device was designed and manufactured using a low cost (˜£1600) consumer grade fused deposition modelling (FDM) Ultimaker 2+ 3D printer with imbedded microfluidic channels 1 mm wide, 400 μm depth and with a volumetric capacity of approximate 23 μl. FDM printers are not typically used, or are capable, of producing the fine detailed structures required for microfluidic fabrication; in addition 3D-printed objects can suffer from poor optical transparency. However, in this work, imbedded microfluidic channels were produced and the optical transparency of the device was improved though manufacture optimisation to such a point that optical colourimetric assays can be performed in a microfluidic cuvette device with sample path length of 500 μm and volumetric capacity of 190 μl. When acetone vapour treatment was used, it was possible to improve transparency of plastic samples by up to a further 30%. The LOAD device is capable of being spun using an unmodified optical disc drive (ODD), demonstrating the centrifugation based separation of plasma from whole blood in a low-cost FDM 3D-printed microfluidic LOAD device. A cholesterol assay and glucose assay was developed and optimised using cholesterol oxidase (ChOx) or glucose oxidase (GlOx) respectively and horseradish peroxidase (HRP) for the oxidative coupling of chromotropic acid (CTA) and 4-aminoantipyrine (AAP). This produced a blue quinoneimine dye with a broad absorbance peaking at 590 nm for the quantification of cholesterol/glucose in solution. The colourimetric enzymatic cascade assays were developed for use within low-cost FDM 3D-printed microfluidic devices to demonstrate the capabilities and functionality of the devices. For comparison, the assay was run in standard 96 well plates with a commercial plate reader. The results demonstrated that the quantification of 0-10 mM glucose solution using a 3D-printed microfluidic optical device had a performance comparable to a plate reader assay; glucose assay in whole blood samples R² = 0.96.
Open Access
Development and application of optical fibre strain and pressure sensors for in-flight measurements
(IOP Publishing, 2016-09-16) Lawson, Nicholas J.; Correia, Ricardo N.; James, Stephen W.; Partridge, Matthew; Staines, Stephen E.; Gautrey, James E.; Garry, Kevin; Holt, Jennifer C.; Tatam, Ralph P.
Fibre optic based sensors are becoming increasingly viable as replacements for traditional flight test sensors. Here we present laboratory, wind tunnel and flight test results of fibre Bragg gratings (FBG) used to measure surface strain and an extrinsic fibre Fabry–Perot interferometric (EFFPI) sensor used to measure unsteady pressure. The calibrated full scale resolution and bandwidth of the FBG and EFFPI sensors were shown to be 0.29% at 2.5 kHz up to 600 με and 0.15% at up to 10 kHz respectively up to 400 Pa. The wind tunnel tests, completed on a 30% scale model, allowed the EFFPI sensor to be developed before incorporation with the FBG system into a Bulldog aerobatic light aircraft. The aircraft was modified and certified based on Certification Standards 23 (CS-23) and flight tested with steady and dynamic manoeuvres. Aerobatic dynamic manoeuvres were performed in flight including a spin over a g-range −1g to +4g and demonstrated both the FBG and the EFFPI instruments to have sufficient resolution to analyse the wing strain and fuselage unsteady pressure characteristics. The steady manoeuvres from the EFFPI sensor matched the wind tunnel data to within experimental error while comparisons of the flight test and wind tunnel EFFPI results with a Kulite pressure sensor showed significant discrepancies between the two sets of data, greater than experimental error. This issue is discussed further in the paper.
Open Access
Development of a pore pressure sensor employing fibre Bragg gratings
(Cranfield University, 2008-12) Gonçalves Correia, Ricardo Nuno; James, Stephen W.; Tatam, Ralph P.
Monitoring pore pressure is important to understand and predict the mechanical behaviour of soil, helping engineers to assess the stability of slopes and built infrastructures. The instrumentation used to monitor pore pressure should provide dense or extended spatial monitoring of the pore pressure and facilitate multiplexing with other sensors to form a multi-parameter monitoring system. The aim of this research was to develop a Fibre Bragg Grating (FBG) pore pressure sensor for soil applications, satisfying the typical measurement requirement of 1 kPa resolution over a 300 kPa measurement range with the potential for multiplexing. The technique used to develop the sensor consisted of transducing pressure into a transverse load applied to the central section of an FBG. This loading configuration induces a narrow spectral drop-out in the reflection spectrum of the FBG that tracks across its bandwidth in response to the applied load. The effect of this loading configuration on the reflection spectrum of a bare FBG was modelled with the aim of optimising the sensor range and resolution. An improvement of the sensor sensitivity to transverse load was obtained using a novel packaging technique that consisted of embedding the central section of the FBG within an epoxy cube. The deformation of the epoxy cube in response to transverse load resulted in the application of an axial strain to the embedded section of the FBG, which improved the load sensitivity. Moreover, this technique provided an efficient protection of the fibre against mechanical damage. A sensor housing was designed to allow the amplification/reduction of the load resulting from the pressure applied to a diaphragm. A pressure resolution of 0.2 kPa over a 100 kPa measurement range was obtained using a 6 mm long FBG with a 2 mm long section embedded in a epoxy cube which satisfies the sensor requisites.
Open Access
Development of the Cranfield University Bulldog Flight Test Facility
(Cambridge University Press, 2017) Lawson, Nicholas J.; Correia, Richardo N.; James, Stephen W.; Gautrey, James E.; Staines, Stephen E.; Partridge, Matthew; Tatam, Ralph P.
Cranfield University’s National Flying Laboratory Centre (NFLC) has developed a Bulldog light aircraft into a flight test facility. The facility is being used to research advanced in-flight instrumentation including fibre optic pressure and strain sensors. During the development of the test bed, computational fluid dynamics (CFD) has been used to assist the flight test design process, including the sensor requirements. This paper describes the development of the Bulldog flight test facility, including an overview of the design and certification process, the in-flight data taken using the installed fibre optic sensor systems and lessons learned from the development programme, including potential further applications of the sensors.