Staff publications (SoE)

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Open Access
A production system variable connectance model
(Cranfield Institute of technology, 1984-02) Burbidge, John L.
Open Access
Electronic speckle pattern surface contouring using optical fibres and wavelength modulation of laser diodes
(International Society for Optical Engineering; 1999, 1990-12-31T00:00:00Z) Tatam, Ralph P.; Davies, Jeremy C.; Buckberry, Clive H.; Jones, Julian D. C.
The incorporation of laser diodes and monomode fibre optics into an Electronic Speckle Pattern Interferometer (ESPI) has led to the development of a novel holographic surface contouring system. Height contours are obtained by switching between two laser wavelengths. Contour intervals from 0.5-5 mm have been generated by modulating the injection current of a single laser diode source and are demonstrated on an automotive disc brake hub.
Open Access
Photorefractive Volume Holographic Demodulation of In-Fiber Bragg Grating Sensors
(IEEE Institute of Electrical and Electronics, 1996-05-05T00:00:00Z) James, Stephen W.; Dockney, Michael L.; Tatam, Ralph P.
A demodulation scheme for an in-fiber Bragg grating sensor using a volume holographic filter formed in photorefractive BaTiO3 is proposed and demonstrated. A strain range of 2500 μstrain, with minimum detectable strain of 4 μstrain/√Hz, is measured. Extension of the technique to allow demodulation of arrays of sensors is discus
Open Access
Very efficient sampling technique for fiber-remote optical emission spectroscopy of aqueous solutions
(1997-01-01T00:00:00Z) MacKenzie, Steven J.; Hodgkinson, Jane; Johnson, Mark; Dakin, John P.; Cecchi, G.; Lamp, T.; Reuter, R.; Weber, K.
We have measured fluorescence from a waveguide formed by a falling cylindrical stream of liquid. The configuration is suited to taking measurements from liquids with any refractive index, such as aqueous solutions. The parameters which determine the stream stability have been investigated, and the optical collection efficiency has been mathematically modelled. We have produced streams up to 350 mm long with a 2.5 mm diameter, and measured a fluorescence collection enhancement factor of 9 from a 100 mm long, 1 mm diameter stream.
Open Access
pH sensor using Langmuir-Blodgett overlays on polished optical fibers
(Optical Society of America, 1997-04-15T00:00:00Z) Flannery, D.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.
Evanescent coupling between a side-polished single-mode optical fiber and a single-mode, pH-sensitive Langmuir-Blodgett overlay is used to demonstrate an intrinsic fiber-optic pH sensor. The sensor shows a wavelength sensitivity of 18.8 ± 0.8 nm/pH and a transmission sensitivity of 9.7 ± 0.8 dB/pH when operating at 750 n
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
Photothermal detection of trace optical absorption in water by use of visible-light-emitting diodes
(Optical Society of America, 1998) Hodgkinson, Jane; Johnson, Mark; Dakin, John P.
Visible light emitting diodes of three different colors have been used to detect an absorbing compound (potassiumpermanganate) in trace quantities in aqueous solution. Photothermal absorption in a closed cell caused deflection of a water meniscus held at a small pinhole. The displacement was monitored using optical fiber interferometry. The technique was limited by LED emission intensities and environmental acoustic noise, giving minimum detectable absorption coefficients of 2x10-4 cm-1 at 478 nm and 658 nm, and 3x10-4 cm-1 at 524 nm. The magnitude and form of meniscus deflection signals were shown to be in good agreement with theory.
Open Access
Photothermal detection of trace compounds in water, using the deflection of a water meniscus
(Iop Publishing Ltd, 1998-01-01T00:00:00Z) Hodgkinson, Jane; Johnson, Mark; Dakin, John P.
Anovelphotothermaldetectorisdescribed,basedonaclosedcellsuitableforusewithlow-frequencymodulatedcontinuous-wavelightsources.Photothermalexpansioninaqueoussamplescausedthedeflectionofawatermeniscusheldacrossa200m-radiuspinhole.Displacementofthewatermeniscuswasmeasuredusingfibreopticinterferometry.Amercurydischargelamp(254nm)andalaserdiode(678nm)wereusedtodetecttoabsorptionby2ppbanthraceneand0.5ppmpotassiumpermanganateinaqueoussolution,respectively.Thetechniquewasusedtodetectdifferencesbetweenabsorptioncoefficientsinaqueoussolutionsdowntoapproximately20%ofthebackgroundabsorptionofthewateritself.
Open Access
Diffusing-wave spectroscopy in randomly inhomogeneous media with spatially localized scatterer flows.
(Springer Science Business Media, 1998-04-01T00:00:00Z) Skipetrov, S. E.; Meglinski, I. V.
Multiple scattering of laser radiation in a randomly inhomogeneous turbid medium with a spatially localized flow of particles is studied. The time autocorrelation function of backscattered light is calculated for the case of a laminar flow of scatterers in a cylindrical capillary embedded in the medium. A new method is proposed and tested experimentally for determining the position of the dynamic region and the dominant form and characteristic velocity of the particle motion there.
Open Access
Pseudo-heterodyne signal processing scheme for interrogation of fiber Bragg grating sensor arrays
(International Society for Optical Engineering; 1999, 1998-12-31T00:00:00Z) Chatterjea, C. K.; James, Stephen W.; Tatam, Ralph P.
An intensity-based interrogation technique for arrays of fiber bragg grating (FBG) sensors is reported. The technique is based upon each FBG forming one mirror of a Michelson interferometer. Source wavelength modulation is combined with an unbalanced interferometer to produce a carrier signal. Carrier frequencies are characteristic of the optical path length imbalance and hence grating position within the array. The intensity of the carrier signal is directly related to the optical power reflected from the grating and hence the strain applied to the grating. Strain resolution of ∼3μm/m is demonstrated with an ∼350μm/m sensor range. Multiplexing is demonstrated and techniques to extend the range are disc
Open Access
Second-harmonic generation in Langmuir-Blodgett waveguide overlays on single- mode optical fiber
(Optical Society of America, 1999-09-30T00:00:00Z) Johal, S. S.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.
Second-harmonic radiation has been obtained from Langmuir-Blodgett films of E-N- octadecyl-4-[2-(4-dibutylaminophenyl)ethenyl] quinolinium octadecylsulfate, deposited as a waveguide overlay upon optical fiber that is single mode at the pump wavelength (lambda = 1064 nm). A quadratic relationship between the pump power and second-harmonic intensity was observed.
Open Access
Fiber-optic chemical sensing with Langmuir-Blodgett overlay waveguides
(Osa Optical Society of America, 1999-12-20T00:00:00Z) Flannery, D.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.
Fiber-optic chemical sensing has been demonstrated with a side-polished single- mode optical fiber, evanescently coupled to chemically sensitive Langmuir- Blodgett (LB) overlay waveguides. The sensors exhibit a channel-dropping response centered on a wavelength that is dependent on the thickness and the refractive index of the overlay waveguide. It has been shown that pH-sensitive organic dyes proved to be suitable materials fur the formation of an overlay waveguide whereas LB deposition provides the required thickness control. A theoretical model of the sensor response, based on the Kramers-Kronig relations and phase matching of the guided modes within the optical fiber and overlay waveguide, shows good agreement with experimental results.
Open Access
Field evaluation of a multi-point fibre optic sensor array for methane detection (“OMEGA”)
(Society of Photo-optical Instrumentation Engineers (SPIE), 2000) Hodgkinson, Jane; Pride, Russ D.; Tandy, Chris; Moodie, Dave; Stewart, George
A multi-point fibre optic sensor array for methane detection (“OMEGA”) has been developed and tested under semiquantitative field conditions. The new system employed wavelength modulation spectroscopy using a DFB laser source scanned across the Q6 methane line at 1.665•m. A branched fibre network connected the single source to up to 64 sensor heads. Controlled releases of natural gas were provided for test purposes within an array of four optical sensors and four pellistor reference sensors. An automated system delivered standard gases to each sensor, to enable routine calibration checks to be carried out. Agreement between the conventional and optical systems was excellent in the range 0-100% LEL (lower explosion limit). The optical system offers a simple, intrinsically safe design with a low cost of ownership per sensor head.
Open Access
Verification of the capacity of Malpensa Airport: Final report
(Cranfield University, College of Aeronautics, 2000-07) Air Transport Group
The purpose of this study is twofold. First, to assess the capacity of Malpensa airport taking into account the impact of environmental measures introduced by the Italian Government Environmental Decree of 13th December 1999. Second, to assess the impact of projected traffic growth in the Milan airport system.
Open Access
Comparison of self-referencing techniques for photothermal detection of trace compounds in water
(Elsevier , 2000-09) Hodgkinson, Jane; Johnson, Mark; Dakin, John P.
Self-referencing techniques are compared for a closed-cell photothermal detector that uses a water meniscus as a pressure sensor. Deflection of the meniscus was measured using an optical fibre Fabry–Perot interferometer. For long measurement integration times, interference fringe drift was a serious limitation on the detection repeatability for non self-referenced measurements. Two self-referencing techniques were compared for measurements of optical absorption. The first technique used a simultaneous reference absorption signal at a second wavelength, and the second used a simultaneous volumetric modulation within the cell. Both methods have been evaluated with photothermal excitation by a 658-nm LED, a 478-nm LED and a UV discharge lamp. For the detection of absorption in aqueous solutions, the two methods had similar performance. However, the volumetric method could be used for detection of any absorbing compound, regardless of its absorption spectrum and was more convenient to use.
Open Access
Experimental study of the potential use of diffusing wave spectroscopy to investigate the structural characteristics of blood under multiple scattering
(Elsevier Science B.V., Amsterdam., 2000-12-01T00:00:00Z) Korolevich, Alexander N.; Meglinski, I. V.
The extension of the photon correlation spectroscopy (PCS) in multiple scattering regime, so-called diffusing wave spectroscopy (DWS) was employed to the study of blood samples. Multiple scattered light from a helium–neon (He–Ne) laser beam incident on the blood samples was detected by a photomultiplier, and both the temporal autocorrelation intensity functions g2(τ) and power spectra S (w) were measured by a spectrum analyzer. The potentials of using DWS for the qualitative and quantitative determination of the structural characteristics of the blood elements were studied experimentally. The experimental studies made, permits the use of DWS for blood cells monitoring in a multiple scattering regime. This paper describes our initial attempts at applying DWS to the study of the discrete blood samples of both healthy donors and patients with the cardiac ischemia. The subsequent experiments provide a verification of DWS of blood cells shape monitoring under multiple scatte
Open Access
Condition monitoring of slow-speed rolling element bearings using stress waves
(Professional Engineering Publishing, 2001-01-01T00:00:00Z) Jamaludin, N.; Mba, David; Bannister, R. H.
Condition monitoring of rolling element bearings through the use of vibration analysis is an established technique for detecting early stages of component degradation. However, this success is not mirrored at rotational speeds below 16r/min. At such speeds the energy generated from bearing defects might not show as an obvious change in signature and thus becomes undetectable using conventional vibration measuring equipment. This paper presents an investigation into the applicability of stress wave analysis for detecting early stages of bearing damage at a rotational speed of 1.12r/min (0.0187 Hz). Furthermore, it reviews work undertaken in monitoring bearings rotating at speeds below 16r/min.
Open Access
Modeling the sampling volume for the skin blood oxygenation measurements
(Springer Science Business Media, 2001-01-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.
Abstract The absolute quantified measurement of haemoglobin skin blood saturation from collected reflectance spectra of the skin is complicated by the fact that the blood content of tissues can vary both in the spatial distribution and in the amount. These measurements require an understanding of which vascular bed is primarily responsible for the detected signal. Knowing the spatial detector depth sensitivity makes it possible to find the best range of different probe geometries for the measurements of signal from the required zones and group of vessels inside the skin. To facilitate this, a Monte Carlo simulation has been developed to estimate the sampling volume offered by fibre-optic probes with a small source-detector spacing (in the current report 250 μm, 400 μm and 800 μm). The optical properties of the modelled medium are taken to be the optical properties of the Caucasian type of skin tissue in the visible range of the spectrum. It is shown that, for a small source-detector separation (800 μm and smaller), rough boundaries between layers of different refractive index can play a significant role in skin optics. Wavy layer interfaces produce a deeper and more homogeneous distribution of photons within the skin and tend to suppress the direct channelling of photons from source to detector. The model predicts that a probe spacing of 250 μm samples primarily epidermal layers and papillary dermis, whereas spacings of 400–800 μm sample upper blood net dermis and
Open Access
Acoustic Emission Signal Classification in Condition Monitoring Using the Kolmogorov-Smirnov Statistic.
(2001-01-01T00:00:00Z) Hall, L. D.; Mba, David; Bannister, R. H.
Acoustic emission (AE) measurement at the bearings of rotating machinery has become a useful tool for diagnosing incipient fault conditions. In particular, AE can be used to detect unwanted intermittent or partial rubbing between a rotating central shaft and surrounding stationary components. This is a particular problem encountered in gas turbines used for power generation. For successful fault diagnosis, it is important to adopt AE signal analysis techniques capable of distinguishing between various types of rub mechanisms. It is also useful to develop techniques for inferring information such as the severity of rubbing or the type of seal material making contact on the shaft. It is proposed that modelling the cumulative distribution function of rub-induced AE signals with respect to appropriate theoretical distributions, and quantifying the goodness of fit with the Kolmogorov-Smirnov (KS) statistic, offer a suitable signal feature for diagnosis. This paper demonstrates the successful use of the KS feature for discriminating different classes of shaft- seal rubbing. A hierarchical cluster algorithm was employed for grouping extracted KS values. AE rub signals were simulated with various metallic seals and measured at the journal bearings of a test rig rotating at approximately 1500 rev/min. Also, the KS classification results were directly compared withmore established AE feature vectors.
Open Access
A comparison of modified K-ε turbulence models for buoyant plumes
(Taylor and Francis, 2001-02-01) Worthy, Jude; Sanderson, V. E.; Rubini, Philip A.
The effect of buoyancy on the production and dissipation of turbulent kinetic energy is investigated in variants of the popular k- ε turbulence model. The standard gradient diffusion model is considered for the scalar flux as well as a generalised gradient diffusion model. Also, the addition of the non-isotropic component of an algebraic stress model for the Reynolds stresses is assessed. The relative significance of the various models and terms are demonstrated using different combinations of the models, including the important flux Richardson correction term. The generalised gradient diffusion and algebraic stress models are shown to give a strong increase in turbulence production, although the effect on the flow can be largely controlled by the coefficient of the flux Richardson term. Recommendations are made regarding optimum models and coefficients.