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WO2003042647A1 - Capteur de deformation - Google Patents

Capteur de deformation Download PDF

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Publication number
WO2003042647A1
WO2003042647A1 PCT/GB2002/005140 GB0205140W WO03042647A1 WO 2003042647 A1 WO2003042647 A1 WO 2003042647A1 GB 0205140 W GB0205140 W GB 0205140W WO 03042647 A1 WO03042647 A1 WO 03042647A1
Authority
WO
WIPO (PCT)
Prior art keywords
strain
force
optic fibre
wavelength selective
sensing element
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2002/005140
Other languages
English (en)
Inventor
Scott Mcculloch
Gary Burnell
Robert Raimund Josef Maier
James Stephen Barton
Julian David Clayton Jones
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UK Secretary of State for Defence
Original Assignee
UK Secretary of State for Defence
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by UK Secretary of State for Defence filed Critical UK Secretary of State for Defence
Priority to GB0411196A priority Critical patent/GB2397882B/en
Publication of WO2003042647A1 publication Critical patent/WO2003042647A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0033—Transmitting or indicating the displacement of bellows by electric, electromechanical, magnetic, or electromagnetic means
    • G01L9/0039—Transmitting or indicating the displacement of bellows by electric, electromechanical, magnetic, or electromagnetic means using photoelectric means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings

Definitions

  • the present invention relates to sensors, in particular strain sensors and most particularly those sensors using wavelength-selective elements, such as Bragg diffraction gratings, disposed within optic fibre.
  • strain sensors especially those made using Bragg diffraction gratings within optic fibres, are relatively insensitive, due to the high stiffness of optic fibres.
  • Several ways have been proposed of increasing the sensitivity of such sensors, such as by using interferometry, but the sensors may still be relatively insensitive.
  • the present invention provides a more sensitive strain sensor.
  • a strain sensor comprising a strain sensing element whose response to interrogation is dependent on the force to which it is subjected, the strain sensing element having a long axis, wherein, in use, the application of a given force to the strain sensing element in a direction substantially aparallel to the long axis induces a greater strain in the strain sensing element than the given force would induce when applied in a direction substantially parallel to the long axis.
  • This provides a strain sensor in which the response is amplified. "Aparallel" is used to indicate that a direction that is not parallel.
  • the strain sensing element is a wavelength selective element, the wavelength selective element being disposed within an optic fibre, the long axis of the strain sensing element being defined as being the longitudinal axis of the optic fibre in the locality of the strain sensing element.
  • optic fibre is often known as optical fibre.
  • the optic fibre is tethered to a substrate at a first and a second point such that the optic fibre therebetween is substantially strain-relieved from the application of force to the optic fibre external of the first and second points, the wavelength selective element being disposed therebetween, wherein, in use, a force is applied between the first and second attachment points.
  • the strain sensor further may further comprise a second wavelength selective element arranged so as to be at substantially the same temperature as the first wavelength selective element and whose response to a given applied force is different from that of the first wavelength element. This permits the effect of temperature on the sensor to be minimised using common mode rejection techniques.
  • the second wavelength selective element may be disposed in series with the first wavelength selective element in between the first and second attachment points further wherein, in use, force is applied between the two wavelength selective elements.
  • the strain sensor may comprise a second wavelength selective element arranged so as to be at substantially the same temperature as the first wavelength selective element and whose response to a given applied force is different from that of the first wavelength element, wherein the second wavelength selective element is arranged such that, in use, the angle tended between the applied force and the longitudinal axis of the optic fibre in the locality of the second wavelength selective element is different from the angle tended between the applied force and the longitudinal axis of the optic fibre in the locality of the first wavelength selective element.
  • the angle between the applied force and the longitudinal axis of the optic fibre in the locality of the second wavelength selective element is preferably less than 5°.
  • strain sensing element is under tension prior to use.
  • the present invention further provides a strain sensor comprising a strain sensing element whose response to interrogation is dependent on the force to which it is subjected, the strain sensing element having a long axis, wherein, in use, the application of a given force to the strain sensing element in a direction substantially aparallel to the long axis induces a greater strain in the strain sensing element than the given force would induce when applied in a direction substantially parallel to the long axis, the strain sensor further comprising a second strain sensing element arranged so as to be at substantially the same temperature as the first strain sensing element and whose response to a given applied force is different from that of the first strain sensing element. This enables the effect of temperature to be minimised by common mode rejection.
  • a preferred embodiment of the present invention discloses a strain sensor whose response to interrogation is dependent on the force to which it is subjected, the strain sensor having a substantially T-shaped spatial geometry and comprises a first arm retained by a first attachment, a second arm retained by a second attachment, a third arm attached at one end to both the first and second arms and arranged substantially perpendicular to the long axis of the first and second arms, wherein the strain sensor comprises at least one strain sensing element, each strain sensing element being mounted on or integral with one of the first and second arms such that, in use, the application of a given force to the third arm in a direction substantially perpendicular to the long axis of the first and second arms induces a greater strain in the strain sensing element or elements mounted on or integral with the first and second arms than the given force induces or would induce in the third arm.
  • This provides a particularly useful sensor geometry. It is preferred that a strain sensing element is mounted on or integral with the third arm. It is further preferred that each strain sensing element
  • the strain sensing element comprises a wavelength selective element incorporated within an optic fibre
  • other strain sensing elements may be used.
  • electrical strain sensors may be used. The resistance of the electrical strain sensor changes as a function of strain.
  • the present invention further provides for an array of sensors comprising a plurality of strain sensors in accordance with the present invention.
  • the strain sensors may be connected in series or parallel. It is preferred that the strain sensors are addressable using conventional multiplexing techniques.
  • a further embodiment of the present invention provides a pressure sensing apparatus comprising at least one strain sensor in accordance with the present invention. Such a pressure sensing apparatus takes advantage of the amplified response of the strain sensor in accordance with the present invention.
  • the pressure sensing apparatus may further comprise a means of interrogating the at least one strain sensor.
  • each strain sensing element comprises a wavelength selective element and the means of interrogating the at least one strain sensor comprises a source of electromagnetic radiation with which the wavelength selective elements interact and a detection system which monitors the radiation from the wavelength selective elements.
  • Figure 1 shows a schematic representation of a sensor in accordance with the present invention using one strain sensing element
  • Figure 2 shows a simple force vector diagram indicating the forces that are present in the strain sensing element used in the sensor of figure 1 ;
  • Figure 3 shows a schematic for the development of an analytical solution for calculating the induced force in the strain sensing element of figure 1
  • Figure 4 shows a graph indicating the measured force in the strain sensing element of the sensor of figure 1, and thus the gain, as a function of the applied force
  • Figure 5 shows a schematic representation of a sensor in accordance with the present invention using two strain sensing elements so that the effects of temperature on the sensor may be minimised
  • Figure 6 shows a schematic graphical representation of the response of the two strain sensing elements of Figure 5 as a function of applied force and temperature;
  • Figure 7 shows a series array of sensors in accordance with the present invention comprising a plurality of sensors in accordance with the present invention
  • Figure 8 shows a schematic cross-section through a pressure sensing apparatus in accordance with the present invention comprising a strain sensor in accordance with the present invention
  • Figure 9 shows the response of a strain sensor in accordance with the present invention when mounted on the pressure sensing apparatus of figure 8 as a function of atmospheric pressure.
  • FIG. 1 shows a schematic representation of a strain sensor in accordance with the present invention, the sensor being in use.
  • the strain sensor comprises a Bragg diffraction grating 3 disposed within an optic fibre 1 that is attached at attachment points 5 and 6 to a substrate 4.
  • the optic fibre 1 is attached to the substrate 4 such that application of force to the optic fibre 1 external of the attachment points 5 and 6 does not affect the strain to which the section of optic fibre 1 between the attachment points 5 and 6 is subjected.
  • a second portion of optic fibre 2 is firmly attached to optic fibre 1 at attachment point 7, the attachment point 7 being equidistant from attachment points 5 and 6.
  • the force F to be sensed is exerted via the second portion of optic fibre 2 to the optic fibre 1. Note that any means of attachment may be used to allow the force, F, to be applied to the optic fibre 1.
  • the strain sensor of figure 1 uses a Bragg diffraction grating 3 as an interrogable strain sensing element.
  • the diffraction grating 3 comprises a periodic fluctuation of refractive index along the length of the optic fibre 1 and may be formed in many ways known to those skilled in the art.
  • the grating structure may be formed by previously subjecting the optic fibre 1 to a standing wave pattern established by two interfering coherent beams from a high power ultra-violet (UV) laser.
  • UV ultra-violet
  • the diffraction grating 3 selectively reflects light according to equation 1 :
  • ⁇ B is the Bragg wavelength
  • n is the effective refractive index of the core of the optic fibre 1
  • A is the pitch of the diffraction grating 3.
  • Both the pitch of the diffraction grating 3 and the refractive index of the optic fibre 1 are sensitive to changes in temperature and strain applied to the optic fibre 1.
  • the diffraction grating 3 may form the sensing element of a strain sensor.
  • the Bragg diffraction grating 3 is approximately 5mm long.
  • the length of optic fibre 1 between attachment points 5 and 7 is about 7mm, this being minimised to optimise the response of the sensor.
  • the application of force, F induces a force F 2 in the section of optic fibre 1 comprising the diffraction grating 3.
  • the applied force, F is approximately normal to the section of optic fibre 1 comprising the diffraction grating 3.
  • the force, F is counterbalanced by the forces (F 2 and F 3 ) induced in the sections of optic fibre between attachment point 7 and attachment points 5 and 6 respectively (see figure 2).
  • the angle, ⁇ is a function of the applied force, F, and the elastic deformation of the optic fibre 1. It can be readily seen that:
  • the gain factor (F 2 /F) of the sensor is thus given by:
  • the force, F 2 , acting on the section of optic fibre 1 between attachment points 5 and 7 induces an axial strain proportional to the applied force F provided that the sensor is operated below the elastic strain limit of the optic fibre 1. Furthermore, the smaller the angle ⁇ , the greater the force F 2 .
  • the force F 2 acting on the section of optic fibre 1 between attachment points 5 and 7 induces a linear extension of this section of optic fibre 1 which in turn affects the angle ⁇ between this section of optic fibre 1 and an imaginary line normal to the applied force, F. This change in angle causes a change in the gain factor (see equation 2). This characteristic leads to a non-linear increase in the force experienced by the diffraction grating 3 with respect to a linear increase in applied force.
  • the force F 2 induced in the section of optic fibre 1 comprising the diffraction grating 3 may be calculated numerically with reference to figure 3 using the following equation: Equation 4
  • a would be the length of the section of optic fibre 1 between attachment points 5 and 7 if that section is not subjected to any strain
  • b is the length of the section of optic fibre 1 between attachment points 5 and 7 when subjected to pre-strain force F 20
  • ⁇ b is the change in length of the section of optic fibre 1 induced by the application of force F
  • ⁇ 0 is the angle tended between the optic fibre 1 when the optic fibre 1 is subjected to pre-strain F 20 and a line normal to the direction in which a force, F, would be applied
  • ⁇ is the angle tended between the optic fibre 1 and a line normal to the direction of application of force, F, when force F is applied to the optic fibre 1
  • E is the Young's Modulus for SiO 2 (72500 N/rnm 2 )
  • A is the cross-section of the optic fibre 1 (0.012272mm 2 ).
  • the force F 2 acting on the diffraction grating 3 generates a linear extension of the optic fibre 1 resulting in a change in the pitch of the diffraction grating 3.
  • the strain sensitivity of a fibre Bragg diffraction grating is well-known and is given in Equation 5
  • the strain in the optic fibre 1 may be calculated using equation 6.
  • Equations 5 and 6 may be combined to calculate the force co-efficient, d ⁇ B /F, of about 1.34nm/N at 1550nm wavelength.
  • d ⁇ B is proportional to the applied force (within the elastic limit of the optic fibre).
  • FIG. 5 shows a strain sensor in accordance with the present invention, the sensor being shown in use.
  • the strain sensor comprises a Bragg diffraction grating 3 disposed within an optic fibre 1 that is attached at attachment points 5 and 6 to a substrate 4.
  • the optic fibre 1 is attached to the substrate 4 such that application of force to the optic fibre 1 external to the attachment points 5 and 6 does not effect the strain to which the section of optic fibre 1 between the attachment points 5 and 6 is subjected.
  • a second portion of optic fibre 2 is firmly attached to optic fibre 1 at attachment point 7, this being equidistant from attachment points 5 and 6.
  • the second portion of optic fibre 2 comprises a Bragg diffraction grating 10.
  • the second portion of optic fibre 2 may be spliced into optic fibre 1 such that transmission of light is permissible between the diffraction gratings 3 and 10. Alternatively, there maybe no light-transmissive path between diffraction gratings 3 and 10.
  • the force F to be sensed is exerted via the second portion of optic fibre 2 to the optic fibre 1.
  • the force Fi experienced by the diffraction grating 10 is substantially the same as the applied force, and thus varies linearly with applied force, F. Both diffraction gratings 3 and 10 are unstrained prior to the application of loading force, F, although it may be desirable to exert a pre-straining force on the optic fibres, 1, 2.
  • the two diffraction gratings 3, 10 are designed to be at essentially the same temperature at all times when the sensor is in use. Furthermore, the responses of the two diffraction gratings 3 and 10 are different for a given applied force. This configuration permits the effect of temperature to be minimised. This is important since the sensing elements used in the present invention, the diffraction gratings 3, 10, are responsive to, inter alia, changes in applied force and temperature. Figure 6 shows how this configuration of sensor operates. Increased temperature causes a change in ⁇ for both diffraction gratings 3, 10.
  • ⁇ (F ) red is independent of temperature
  • ⁇ is the measured Bragg wavelength for diffraction grating 3 under load at a given temperature
  • ⁇ , ⁇ is the measured Bragg wavelength for diffraction grating 10 under load at a given temperature
  • ⁇ , 2 ,o is the Bragg wavelength for unstrained diffraction grating 3 at a given temperature
  • ⁇ , ⁇ ,o in the Bragg wavelength for unstrained diffraction grating 10 at a given temperature.
  • the sensors of the present invention may be incorporated into arrays that allow the sensing of strain, preferably simultaneously, in many different places.
  • Figure 7 shows a series array in accordance with the present invention, the array comprising a plurality of sensors 50, 51, 52, 53, 54 in accordance with the present invention.
  • the sensors are addressed via an optic fibre 55 using conventional addressing techniques known to those skilled in the art, such as wavelength-dependent multiplexing. Other array arrangements will be apparent to those skilled in the art.
  • FIG. 8 shows a schematic cross-section through a pressure sensing apparatus in accordance with the present invention comprising a strain sensor in accordance with the present invention.
  • the pressure sensing apparatus comprises a bellows mechanism located within a housing structure.
  • the housing structure comprises several mutually detachable components, a main body 104, an upper extension body 102, a lower extension body 105 and a body seal 106. The detachability permits easy assess to the bellows mechanism.
  • the bellows mechanism comprises a head plate 120 attached to a bellows 108 which is contained within the housing structure, an anchor rod 121 abutted on to the head plate 120 and extending out of the housing structure and a compression spring 103 mounted on a spring carrier 109.
  • the inside of the bellows 108 is evacuated. Change in the atmospheric pressure acting on the outside of the bellows 108 causes a change in the compressive force acting against the effective spring constant of the bellows 108. This leads to compression or expansion of the bellows 108, the degree of compression or expansion depending on the external pressure and the spring constant of the bellows 108. Motion of the bellows 108 is transmitted to motion of the head plate 120 and attached anchor rod 121.
  • a strain sensor 130 in accordance with the present invention is attached to a platform 101 that is attached to the upper body extension 102.
  • the strain sensor 130 is essentially the same as that shown in figure 5.
  • Optic fibre 1 comprising a diffraction grating 3 is attached to the platform 101 at attachment points 5 and 6.
  • Optic fibre 2 comprises diffraction grating 10 and is attached to optic fibre 1 at the mid-point between attachment points 5 and 6.
  • the optic fibre 2 is attached at attachment point 11 to the anchor rod 121.
  • Optic fibre 2 is substantially normal to optic fibre 1, but a small pre-strain is applied to the sensor arrangement such that a slight N-shaped arrangement is formed (with reference to figure 3, ⁇ 0 is greater than about 0.2°).
  • the effective cross-sectional area of the bellows 108 is about 0.16cm 2 .
  • the bellows 108 are thin walled electro-formed nickel bellows with an outside diameter of 6.35mm. Prior to use, the bellows 108 is compressed to about two thirds of its maximum working stroke at the maximum required operating pressure.
  • the compression spring 103 allows for fine tuning of the sensing apparatus' spring constant and to prevent over- compression of the bellows 108 (and associated damage) at high pressures.
  • the maximum deflection of the anchor rod 121 is about 0.5mm.
  • a resolution of about 2mbar is achievable. This is significantly inferior to that required for the present application i.e. significantly inferior to the resolution required of less than lmbar over a range of 500 to 1 lOOmbar.
  • Using the strain sensor 130 in accordance with the present invention then a resolution of about 0.03mbar is attainable due to the increased force induced in the diffraction grating 3.
  • Figure 9 shows data collected using the pressure sensing apparatus of the present invention. Gains of between 6 and 12 are achievable. The amplified response gives rise to better resolution of the pressure sensing apparatus.
  • both diffraction gratings 3 and 10 will be at substantially the same temperature at any given time. Hence, the effect of temperature may be minimised using common mode rejection as previously described.
  • the diffraction gratings 3, 10 are interrogated in reflection using a fibre coupled broadband source (SLED) (not shown) centred at 1545nm (40nm bandwidth at -3dB) followed by a fibre optic 3-port circulator (not shown).
  • SLED fibre coupled broadband source
  • the spectral characteristics of the reflected light is analysed by a scanning Fabry-Perot filter (not shown) with a finesse of -250 at 40nm FSR (Queensgate DMC300C) which is connected to port 3 of the circulator.
  • the Fabry-Perot filter is scanned over the spectral region of interest using digital addressing of an integrated digital-to-analogue converter with a step size of approximately 3pm per step.
  • Data are recorded on a personal computer via a multifunction data acquisition system controlled from a LabNiew VI, National Instruments Inc., USA.
  • the centre of the near Lorentzian bell-shaped spectral reflectance curve is determined by a curve fitting routine in ORIGIN (Microcal Inc., USA) using a Levenberg-Marquardt iteration scheme. It is estimated that, at the given signal/noise ratio of the system, a resolution of better than .3pm can be achieved for the location of the of the peak centre using around 150 points between the full width-half maximum points of the curve.
  • sensors, sensor arrays and pressure sensing apparatus in accordance with the present invention all use Bragg gratings disposed within optic fibres as strain sensing elements. It is anticipated that alternative strain sensing elements may be used. Any interrogable strain sensing element that shows an elastic response with applied force may be used. For example, resistive elements may be used

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optical Transform (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

L'invention concerne un capteur de déformation comprenant un élément de détection de déformation dont la réponse à une interrogation dépend de la force à laquelle il est soumis, l'élément de détection de déformation possédant un long axe. Lorsque le capteur est utilisé, l'application d'une force donnée sur l'élément de détection de déformation dans un sens sensiblement non parallèle par rapport au long axe induit une déformation plus importante que celle que la force donnée induirait si elle était appliquée dans un sens sensiblement parallèle par rapport au long axe. Ce capteur est caractérisé en ce que l'élément de détection de déformation est un élément sélecteur de longueur d'onde disposé dans une fibre optique, en ce que le long axe de l'élément de détection de déformation est défini comme l'axe longitudinal de la fibre optique à proximité de l'élément de détection de déformation, en ce que la fibre optique est ancrée sur un substrat au niveau de premier et second points, de manière que la fibre optique située entre ceux-ci soit sensiblement exempte de déformation émanant de l'application de force sur la fibre optique qui est externe par rapport aux premier et second points, en ce que l'élément sélecteur de longueur d'onde est disposé entre ceux-ci et en ce que, pendant l'utilisation, une force est appliquée entre les premier et second points de fixation.
PCT/GB2002/005140 2001-11-15 2002-11-13 Capteur de deformation Ceased WO2003042647A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0411196A GB2397882B (en) 2001-11-15 2002-11-13 Strain sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0127497A GB0127497D0 (en) 2001-11-15 2001-11-15 Strain sensor
GB0127497.6 2001-11-15

Publications (1)

Publication Number Publication Date
WO2003042647A1 true WO2003042647A1 (fr) 2003-05-22

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3441792C1 (de) * 1984-11-15 1985-11-28 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München Faseroptischer Kraftsensor, insbesondere Drucksensor
US5490427A (en) * 1994-10-17 1996-02-13 Fanuc Usa Corporation Six axis force sensor employing multiple shear strain gages
WO1999032862A1 (fr) * 1997-12-05 1999-07-01 Optoplan As Capteurs a fibres optiques
WO2001020377A1 (fr) * 1999-09-10 2001-03-22 Siemens Aktiengesellschaft Procede pour produire un reseau optique sur un guide d'onde optique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3441792C1 (de) * 1984-11-15 1985-11-28 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München Faseroptischer Kraftsensor, insbesondere Drucksensor
US5490427A (en) * 1994-10-17 1996-02-13 Fanuc Usa Corporation Six axis force sensor employing multiple shear strain gages
WO1999032862A1 (fr) * 1997-12-05 1999-07-01 Optoplan As Capteurs a fibres optiques
WO2001020377A1 (fr) * 1999-09-10 2001-03-22 Siemens Aktiengesellschaft Procede pour produire un reseau optique sur un guide d'onde optique

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
LIU Y ET AL: "OPTICAL BEND SENSOR BASED ON MEASUREMENT OF RESONANCE MODE SPLITTING OF LONG-PERIOD FIBER GRATING", IEEE PHOTONICS TECHNOLOGY LETTERS, IEEE INC. NEW YORK, US, vol. 12, no. 5, May 2000 (2000-05-01), pages 531 - 533, XP000950320, ISSN: 1041-1135 *
MIYAZAKI A ET AL: "GAS PRESSURE MONITORING SYSTEM FOR GIL USING FIBER-OPTIC GAS DENSITY SENSORS", IEEE POWER ENGINEERING SOCIETY 1999 WINTER MEETING. NEW YORK, NY, JAN. 31 - FEB. 4, 1999, NEW YORK, NY: IEEE, US, vol. 1, 31 January 1999 (1999-01-31), pages 221 - 226, XP000898202, ISBN: 0-7803-4894-X *

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Publication number Publication date
GB2397882B (en) 2005-11-09
GB2397882A (en) 2004-08-04
GB0127497D0 (en) 2002-01-09
GB0411196D0 (en) 2004-06-23

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