Browsing by Author "Chehura, Edmon"
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Item Open Access All-electronic frequency stabilization of a DFB laser diode(Cranfield University, 2017-05-11 13:27) Asmari, Abdullah|Hodgkinson, Jane; Chehura, Edmon; Staines, Stephen; Tatam, RalphData to support the paper All-electronic frequency stabilization of a DFB laser diode A Asmari, J Hodgkinson, E Chehura, SE Staines and RP Tatam Optics Express 25 (10), 11679-11691, 2017. Doi: 10.1364/OE.25.011679Item Open Access All-electronic frequency stabilization of a DFB laser diode(Optical Society of America, 2017-05-10) Asmari, A.; Hodgkinson, Jane; Chehura, Edmon; Staines, Stephen E.; Tatam, Ralph P.A laser diode’s junction voltage is a sensitive measure of its temperature and can be used in a thermal control feedback loop. To compensate for the temperature dependence of the laser’s internal resistance, we have measured the dynamic resistance, ∂V/∂I, by modulating the injection current and measuring the demodulated voltage. The junction voltage was thus controlled while operating at fixed DC injection current. Over an external temperature range of 15°C to 35°C, this stabilised the centre frequency (wavelength) of a 1651 nm DFB laser diode with a residual mean frequency shift of 60 MHz (0.5pm), less than the uncertainty on the centre frequency of 80 MHz (0.7 pm). Under the same conditions, conventional thermistor control gave a systematic wavelength shift of −8.4 GHz (−76 pm), and control of the uncompensated forward voltage gave a shift of 9.9 GHz (90 pm).Item Open Access Application of fibre optic sensing systems to measure rotor blade structural dynamics - underlying data(Cranfield University, 2021-03-12 09:17) James, Stephen; Kissinger, Thomas; Tatam, Ralph; Barrington, James; Chehura, Edmon; Weber, Simone; Mullaney, Kevin; Zanotti Fragonara, Luca; Petrunin, Ivan; Staines, StephenRefer to the paper for full details. Fig9a.csv: Comparison of the Power Spectral Density (PSD) of data recorded by the direct optical fibre shape sensing system, an optical fibre Bragg grating strain sensor and a 1D accelerometer with finite element modeling predictions, measured on the top surface of an Airbus Helicopters H135 bearingless main rotor blade on the quarter chord line at approximately 40% rotor radius. Fig9b.csv: Comparison of the Power Spectral Density (PSD) of data recorded by the direct optical fibre shape sensing system, an optical fibre Bragg grating strain sensor and a 1D accelerometer with finite element modeling predictions, measured on the top surface of an Airbus Helicopters H135 bearingless main rotor blade on the quarter chord line at approximately 60% rotor radius. Fig10_FBG_top.csv: Power Spectral Density (PSD) of the 7th fibre Bragg grating strain (FBG) sensor (FBG7) in the three FBG arrays bonded to the top surface of the Airbus Helicopters H135 bearingless main rotor blade, located at approximately 60% rotor radius. Fig10_FBG_bottom.csv: Power Spectral Density (PSD) of the 7th fibre Bragg grating strain sensor (FBG7) in the three FBG arrays bonded to the bottom surface of the Airbus Helicopters H135 bearingless main rotor blade, located at approximately 60% rotor radius. Fig11.csv: Time series of raw data of 3F frequency input collected at approximately 60% rotor radius for the accelerometer, fibre Bragg grating strain sensor and direct optical fibre shape sensor (vertical direction). Fig12.csv: Comparison of Power Spectral Density (PSD) for the 3F mode measured at approximately 60% rotor radius by the accelerometer, fibre Bragg grating strain sensor and direct optical fibre shape sensor (vertical direction). Fig14.csv: Mode shapes measured using the direct optical fibre shape sensor Fig15.cvs: Comparison of normalised displacement mode shapes measured using a 1D accelerometer, the direct optical fibre shape sensor with the finite element model prediction Fig16.csv: Normalised angle measurements performed by the direct optical fibre shape sensor with the ouput from the FE model for Mode 5F Fig17.csv:Comparison of normalised strain mode shapes determined by the FBG strain sensors and the output from the FE model.Item 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.Item 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 °Item Open Access Data supporting: 'Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: data for the measurement of shape'(Cranfield University, 2022-09-01 15:50) Kissinger, Thomas; James, Stephen; Weber, Simone; Mullaney, Kevin; Chehura, Edmon; Barrington, James; Staines, Stephen; Tatam, RalphFSI_Phase_Data_Shape_CORD.csv contains the raw phase data from the three Fibre Segment interferometry array installed on the Direct Optical Fibre Shape Sensing Rod described in the paper: "Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run - part 2: measurement of shape", Smart Materials and Structure, online 25 May 2022. Shape_Data_Vertical_CORD.csv contains the processed shape data in the vertical (flapping) direction, for the T&B2 ground run. Note that the position measurements are relative to the first FSI reflector on the rod, not to the centre of rotation of the blade. Shape_Data_Horizontal_CORD.csv contains the processed shape data n the horizontal (lagging) direction, for the T&B2 ground run. Note that the position measurements are relative to the first FSI reflector on the rod, not to the centre of rotation of the blade.Item Open Access Data supporting: 'Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: data for the measurement of strain'(Cranfield University, 2022-09-01 15:49) James, Stephen; Kissinger, Thomas; Weber, Simone; Mullaney, Kevin; Chehura, Edmon; Barrington, James; Tatam, RalphFBG_Data_CORD.csv contains the raw wavelength data from the 10 FBGs (G1-G10) recorded during the ground run detailed within the paper "Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run - part 1: measurement of strain", James et al. Smart Materials and Structures, available online, May 2022. The unit of the "Time" column is seconds, while the units of columns G1-G10 are nanometers. FSI_Data_CORD.csv contains the raw phase data obtained from the interferometers formed between the reflectors (R1-R10,) and the cleaved end of the optical fibre, recorded during the ground run detailed within the paper The unit of the "Time" column is seconds, while the units of columns R1-R10 are radians.Item Open Access Fabrication of fiber optic long period gratings operating at the phase matching turning point using an ultraviolet laser(Optical Society of America, 2014-06-12) Wong, Rebecca Y. N; Chehura, Edmon; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.It is known that optical fiber long period gratings (LPGs) exhibit their highest sensitivity to environmental perturbation when the period is such that the phase matching condition is satisfied at its turning point. The reproducible fabrication of LPGs with parameters satisfying this condition requires high resolution control over the properties of the grating. The performance of an LPG fabrication system based on the point-by-point UV exposure approach is analyzed in this paper, and the control of factors influencing reproducibility, including period, duty cycle, and the environment in which the device is fabricated, is explored.Item Open Access Fibre Bragg grating based effective soil pressure sensor for geotechnical applications(International Society for Optical Engineering; 1999, 2009-12-31T00:00:00Z) Correia, Ricardo N.; Li, Jin; Staines, Stephen E.; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.; Kutner, Joel; Dewhurst, Paul; Ferreira, PedroAn effective-soil-pressure sensor for geotechnical applications based on Fibre Bragg Gratings is presented. The sensor simultaneous measures total soil pressure and pore pressure, allowing the calculation of the effective stress of soil. Calibration of the sensor using pressurised air demonstrated a pressure sensitivity of 2.02x10 ± 2.84x10nm/kPa and 1.87x10 ± 6.88x10nm/kPa for the total and pore pressure respectively. This corresponds to a pressure resolution of 4.95x10 kPa and 5.46x10kPa for total and pore pressure using a 1pm interrogation system. Measurements undertaken in two types of soil demonstrated dependence of the total pressure sensitivity on soil density/stiffness. Pore pressure measurements agreed well with the preliminary calibratioItem Open Access A fibre Bragg grating based inclinometer system for ground movement measurement(International Society for Optical Engineering; 1999, 2010-12-31T00:00:00Z) Li, Jin; Correia, Ricardo N.; Chehura, Edmon; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.The measurement of ground movement is an essential part of many geotechnical engineering operations. For decades, inclinometer systems have traditionally been used for this purpose to provide crucial information to engineers and researchers. However, conventional inclinometer systems have their limitations, such as high cost and poor durability. In this paper a fibre optic based inclinometer system is reported, which utilizes fibre Bragg grating sensors attached to the casing of a conventional inclinometer. The characterization of the sensor revealed good agreement with theory and conventional displacement measurements. For a casing of length 2.5 m, the minimum measureable deflection of the top of the casing was found to be 0.48 mm when the FBGs were interrogated with a 1 pm wavelength resolution system.Item Open Access Fibre grating refractometer sensors for composite process monitoring(2007-06-17T00:00:00Z) Buggy, Stephen J.; Chehura, Edmon; Skordos, Alexandros A.; Dimopoulos, A.; James, Stephen W.; Partridge, Ivana K.; Tatam, Ralph P.; Osten, W.; Gorecki, C.; Novak, E. L.Optimum performance from advanced composites requires careful control of the resin matrix during cure. This is to ensure there are no cure induced voids and to minimise the build up of internal stresses. Careful control of the process is also necessary to reduce wastage. Traditional resin inspection techniques are bulk or sample oriented and thus cannot provide data about critical component parts. Optical fibre based sensors however, allow for in-situ monitoring techniques to be deployed in components without effecting their structural integrity. In this work, two fibre optic grating techniques are demonstrated as process monitoring sensors and are compared with a Fresnel refractometric method. The change in refractive index of a resin has previously been used as a means for assessing the degree of cure. The central wavelength of an attenuation band of a long period grating (LPG) was monitored during the cure of a resin. In parallel the spectral resonances of a tilted fibre Bragg grating (FBG) are also monitored. The two techniques are shown to correlate well with the Fresnel based method in both detecting the resin and monitoring the state of cure, indicating the potential of the techniques for online production monitoringItem Open Access High sensitivity pressure measurement using optical fibre sensors mounted on a composite diaphragm(Cranfield University, 2021-01-21 17:44) James, Stephen; Aime, Laura; Kissinger, Thomas; Chehura, Edmon; Tatam, RalphData underlying the work presented in the paper "High sensitivity pressure measurement using optical fibre sensors mounted on a composite diaphragm", published in Optics Express, 2020. Each zip file contains the data and a text file describing the contents. Full details are provided in the paperItem Open Access In-line fibre-optic laser doppler velocimeter using bragg grating interferometric filters as frequency to intensity transducers(2002-06) Chehura, Edmon; Tatam, Ralph P.Three dimensional complex flows particularly those of turbomachinery present challenges to current measurement technology in terms of restricted optical access, measurement accuracy for the on-axis velocity component, the need to resolve flow turbulence and measurement difficulty from close to surface or intra-channel measurements in rotating machinery. A novel non-intrusive in-line fibre-optic laser Doppler velocimeter is presented specifically for the measurement of the on-axis component of velocity. The measurement principle is based on a Doppler frequency to intensity transducer in the form of a fibre-optic Bragg grating based Fabry-Perot interferometric filter. The filters were fabricated at 514.5 nm but in principle any desired wavelength may be used thus permitting any laser wavelength source to be used. Filters with appropriate features were designed with the aid of the theoretical models based on the coupled mode theory and transfer matrix approach. The argon-ion laser emission wavelength was locked to a corresponding Doppler broadened absorption line of molecular iodine vapour while the Fabry-Perot interferometer phase was controlled in an independent feedback system using digital lock-in amplifiers. The optical frequency was stabilized to within 10 MHz for at least one hour while the phase was controlled to an equivalent of (within) ± 3 MHz in frequency. Both feedback loops utilized custom designed PID electronic circuit controllers. The bandwidth of the filter was tunable by up to 400 MHz, with a resolution of between 0.2 ms'1 and 1 ms"1, and a sensitivity range of between 0.5 [GHz]'1 and 1.7 [GHz]'1. In this technique the filter was tuned to the optical wavelength, rather than tuning the laser wavelength to match the filter. The finished instrument was applied to the measurement of the on-axis component of velocity, of a rotating disc, over an available range of up to ± 42 ms'1, limited only by the maximum velocity of the disc. The detection system was reconfigured for low velocity measurements at twice the sensitivity over a velocity range of ± 7 ms'1. This technique demonstrates a unique contribution to fluid dynamics for the measurement of the traditionally difficult in-line component of velocity.Item Open Access Interferometric fibre-optic curvature sensing for structural, directional vibration measurements(SPIE, 2017-06-26) Kissinger, Thomas; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.Dynamic fibre-optic curvature sensing using fibre segment interferometry is demonstrated using a cost-effective rangeresolved interferometry interrogation system. Differential strain measurements from four fibre strings, each containing four fibre segments of gauge length 20 cm, allow the inference of lateral vibrations as well as the direction of the vibration of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range over a 21 kHz interferometric bandwidth demonstrate the suitability of this approach for highly sensitive fibre-optic directional vibration measurements, complementing existing laser vibrometry techniques by removing the need for side access to the structure under test.Item Open Access Laser-frequency locking techniques for high-sensitivity strain measurements by high-birefringence fiber Bragg gratings and resonators(International Society for Optical Engineering; 1999, 2007-12-31T00:00:00Z) Salza, M.; Gagliardi, G.; Di Maio, A.; Ferraro, P.; De Natale, P.; Chehura, Edmon; Tatam, Ralph P.; Antonello, Cutolo; Brian, Culshaw; José, Miguel López-HigueraA new approach to simultaneously interrogate orthogonal axes of single Fiber- Bragg-Gratings (FBGs) and FBG-FabryPerot resonator sensors fabricated in linearly highly birefringent (HiBi) fibre is presented. Novel interrogation techniquesof single Fiber-Bragg-Gratings (FBGs) and FBG-resonator sensors are presented. For a single FBG, we combined alaser-modulation technique to an electronic feedback loop that keeps the source always frequency locked to one peak ofthe sensor's reflected spectrum. Two different lasers, with orthogonally- polarized states, were adopted to monitorsimultaneously both the "fast" and "slow" FBG peaks. The corresponding correction signals from the servo-loop outputscan be interpreted as strain or temperature induced on the FBG. Detection limits ranging from 1 nε/√Hz to 100 nε/√Hz,for axial dynamic and static deformations, respectively, and of 0.025 °C/√Hz for temperature variations, are expected. Asimilar approach was developed for sub-pϵ resolution interrogation of an optical resonator made of a high-reflectivityFBG-pair, using the Pound- Drever-Hall (PDH) stabilizatiItem Open Access Locally pressed fibre Bragg grating pressure sensor(2006-12-31T00:00:00Z) Correia, Ricardo N.; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.A spectral-hole created by locally pressing a fibre Bragg grating exhibited a wavelength-shift within the FBG bandwidth. A sensitivity of 74.3pm/(N/mm) was obtained for pressure applied along the slow axis of a high birefringence fibre.Item Open Access Multi-component strain development in superconducting magnet coils monitored using fibre Bragg grating sensors fabricated in highly linearly birefringent fibre(Institute of Physics, 2011-12-31T00:00:00Z) Chehura, Edmon; Buggy, Stephen J.; James, Stephen W.; Johnstone, Adam; Lakrimi, M’hamed; Domptail, Fred; Twin, Andrew; Tatam, Ralph P.The commissioning of superconducting magnet coils was monitored using embedded optical fibre Bragg grating sensors (FBG) fabricated in highly linearly birefringent (HiBi) fibre. The HiBi FBG sensors monitored the internal strain developed in the coils during the energization of the coils. The development of multiple components of strain in the coils when the magnet was energized and quenched was monitored, revealing phenomena that it had not been previously possible to measure using other sensor technologies.Item Open Access Multiplexing a serial array of tapered optical fibre sensors using coherent optical frequency domain reflectometry(Iop Publishing Ltd, 2012-08-01T00:00:00Z) Jarzebinska, Renata; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.The use of high spatial resolution optical frequency domain reflectometry (OFDR) to facilitate the multiplexing of a serial array of tapered optical fibre sensors is presented. Changes in the attenuation of the Rayleigh backscattered signal from the tapered regions are used to monitor the refractive index of the surrounding medium. The use of an array of five tapered regions to monitor liquid flow is demonstrated. An analysis of the performance of the system shows that, for tapers of diameter 50µm, up to nine tapers could be multiplexed using commercial OFDR instrumentation.Item Open Access Multiplexing curvature sensors using fibre segment interferometry for lateral vibration measurements(SPIE - International Society for Optics and Photonics, 2017-04-23) Kissinger, Thomas; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.Dynamic fibre-optic curvature sensing is demonstrated by interrogating chains of fibre segments, separated by broadband Bragg grating reflectors, using range-resolved interferometry (RRI). Four fibre strings, containing four fibre segments each of gauge length 20 cm, are attached to the opposing sides of a support structure and the resulting differential strain measurements allow inference of lateral displacements of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range at an interferometric bandwidth of 21 kHz demonstrate the suitability of this approach for highly sensitive and cost-effective fibre-optic directional vibration measurements of smart structures. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use onlyItem Open Access On-line monitoring of multi-component strain development in a tufting needle using optical fibre Bragg grating sensors(Institute of Physics, 2014-05-20T00:00:00Z) Chehura, Edmon; Dell'Anno, Giuseppe; Huet, Tristan; Staines, Stephen E.; James, Stephen W.; Partridge, Ivana K.; Tatam, Ralph P.Dynamic loadings induced on a tufting needle during the tufting of dry carbon fibre preform via a commercial robot-controlled tufting head were investigated in situ and in real-time using optical fibre Bragg grating (FBG) sensors bonded to the needle shaft. The sensors were configured such that the axial strain and bending moments experienced by the needle could be measured. A study of the influence of thread and thread type on the strain imparted to the needle revealed axial strain profiles which had equivalent trends but different magnitudes. The mean of the maximum axial compression strains measured during the tufting of a 4-ply quasi-isotropic carbon fibre dry preform were - 499 ± 79 με, - 463 ± 51 με and - 431 ± 59 με for a needle without thread, with metal wire and with Kevlar® thread, respectively. The needle similarly exhibited bending moments of different magnitude when the different needle feeding configurations were used.