GB2283567A - Fibre optic sensor device - Google Patents
Fibre optic sensor device Download PDFInfo
- Publication number
- GB2283567A GB2283567A GB9421832A GB9421832A GB2283567A GB 2283567 A GB2283567 A GB 2283567A GB 9421832 A GB9421832 A GB 9421832A GB 9421832 A GB9421832 A GB 9421832A GB 2283567 A GB2283567 A GB 2283567A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fibre
- housing
- sensor
- sensor according
- fibre ends
- 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.)
- Granted
Links
- 239000000835 fiber Substances 0.000 title claims abstract description 74
- 239000000463 material Substances 0.000 claims abstract description 35
- 239000013307 optical fiber Substances 0.000 claims abstract description 9
- 238000006073 displacement reaction Methods 0.000 claims description 15
- 230000005855 radiation Effects 0.000 claims description 11
- 238000004519 manufacturing process Methods 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 7
- 238000005452 bending Methods 0.000 claims description 4
- 238000012544 monitoring process Methods 0.000 description 9
- 230000003287 optical effect Effects 0.000 description 6
- 238000000926 separation method Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000003776 cleavage reaction Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000007017 scission Effects 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Optical Transform (AREA)
Abstract
An optical fibre is cleaved to provide facing fibre ends which are fixed in a housing to form a sensor where any change in the spacing between the fibre ends then alters the amount of light transmitted through the abutting sections of fibre. A vibration sensor is provided by having one or both of the fibre ends spaced from the bore of the housing so as to be movable in a direction perpendicular to the axis of the bore when the housing is vibrated. The sensor can be placed in a material to be cured such that the material flows into the space between the fibre ends via an aperture in the housing. The degree of curing is sensed by detecting the change in refractive index of the curing material. Other embodiments are described that sense tensile stress and temperature. <IMAGE>
Description
SENSOR DEVICE
This invention is concerned with sensors, in particular with a basic displacement sensor which can be used in construction of sensors for other measurands such as strain, temperature, vibration and cure monitoring.
A sensor is sought which is small, simple, rugged, sensitive, which can be inserted in inaccessible positions and even be fully embedded.
Accordingly, the invention proposes a sensor comprising a channel device which is in two discontinuous parts which can transmit radiation along the channel device when said parts are closely adjacent, and a measuring device which measures the variation of the radiation received when one part is displaced relative to the other, the attenuation being a measure of the amount of the displacement.
Preferably, the channel device is an optical fibre which is cleaved but in which the ends of the fibres abut at the cleavage. The radiation may be light, which 'spills out' at the cleavage when the ends are moved slightly apart or are moved so that the axes no longer coincide.
Other forms of channel or of radiation are conceivable.
In the preferred embodiment, the channel device comprises an optical fibre including first and second facing fibre ends, the measuring device being coupled so as to measure the radiation received at the second fibre end; the first and second fibre ends being fixed in a bore of a housing. Changes in the location of the fibre ends relative to one another cause changes in the radiation received at the second fibre end and thereby a measure of the parameter which causes movement of the fibre ends.
The housing may be resilient so as to expand or contract when stress is applied thereto, thereby to alter the spacing between the first and second fibre ends. With this arrangement, the sensor can be used as a strain gauge.
The housing may be formed of a material having a predetermined coefficient of thermal expansion so as to expand or contract with changes in ambient temperature, thereby to alter the spacing between the first and second fibre ends. This embodiment can be used as a temperature sensor.
Preferably, the coefficient of expansion of the housing is high relative to that of the fibre.
Advantageously, at least one of the first and second fibre ends is spaced from the bore of the housing and movable in a direction transverse to the axis of the bore. The or each fibre end will provide a measure of vibration of the sensor as a result in lag in movement of the fibre end relative to movement of the housing.
In another embodiment, the first and second fibre ends are spaced from one another, a material being disposed in the space between the fibre ends, the material having an index of refraction able to change, thereby to change the angle of acceptance for the fibre and the amount of radiation received by the second fibre end. The sensor can be made to measure the parameter which causes the change in the refractive index of the material.
Preferably, the housing includes an aperture which communicates with the space between the first and second fibre ends, enabling material to pass into the space, the index of refraction of the material changing during curing thereof.
The various types of sensor described above could be combined to provide a single device capable of sensing various parameters.
According to another aspect of the present invention, there is provided a method of making a sensor of the type specified, comprising the steps of embedding the optical fibre in the housing and applying a tensile stress to ends of the fibre extending out of the housing so as to cleave the fibre within the housing to form the first and second facing fibre ends.
Preferably, a notch is made in the fibre before embedding the fibre in the housing. In this manner, when a tensile stress is applied to the fibre, it is cleaved at the location of the notch.
The tensile stress is preferably applied to the fibre by bending the housing.
An alternative method of making a sensor of the type specified includes the steps of cleaving an optical fibre so as to provide first and second fibre ends, disposing the first and second fibre ends in facing relationship, and fusing a housing over the first and second fibre ends.
Preferably, the first and second fibre ends are disposed at a predetermined spacing from one another prior to fusing the housing thereover.
In order that the invention shall be clearly understood, various exemplary embodiments will now be described with reference the accompanying drawings, in which:
Fig.l Underlying principle of operation of the sensors according to the invention;
Fig. 2 shows the sensor adapted to a strain gauge;
Fig.3 shows a graph illustrating the predicted behaviour of the gauge of Fig.2;
Fig.4 shows the comparison of actual and predicted behaviour; Fig.5 shows a method of manufacture of a sensor;
Fig.6 shows a vibration sensor; and
Fig.7 shows a cure monitoring sensor.
The underlying principle of operation of the above mentioned sensor is shown in Fig. 1. The device relies upon a very simple attenuation principle between two cleaved fibres, and the way this attenuation varies with displacement.
The proportion of light from the light cone that the second fibre 'sees' can be calculated using the geometry of the fibres and the separation of the fibres. The very large attenuation for very small displacements of the fibres, means that this arrangement not only makes a practical displacement sensor, but can also be used to fabricate sensors for other measurands such as strain, temperature, vibration and cure monitoring.
The sensitivity of this and all the following sensors can be 'tuned' by placing an intermediate opticallytransmitting material between the two fibre end-faces.
This has the effect of altering the acceptance angle for the fibre and thus the attenuation for any given displacement.
A novel strain sensor is shown in Fig. 2. Two cleaved fibres are butted against each other inside a precision bore fixture, and the fibre ends are then fixed into place within the bore. This assembly can then be either surface mounted, or embedded within a material.
Operation of the sensor requires deformation of the precision bore fixture or the optical fibres. This then leads to a small displacement of the fibres. The attenuation of the sensor can be measured or calculated for a given set of conditions if the material properties are known.
The behaviour of this sensor has been calculated for a silica 50/125 im multimode fibre, for various sensor gauge lengths from 10 mm to 80 mm. In the calculation a 'standard' fibre was assumed, detail as follows:
(a) Core index of 1.460
(b) Cladding index of 1.445
(c) Numerical aperture of 0.2065
(d) Acceptance angle of 11.9160
The advantages of this technique over other strain sensors are:
(i) The device is relatively simple to construct.
(ii) Strain is detected by measuring the attenuation
of light.
(iii) The sensor is relatively 'rugged' with a fixed
reference of initial attenuation, whereas most
interferometer arrangements can lose their
reference.
(iv) The sensor can be easily embedded into materials,
with minimal effect on the mechanical properties
(the diameter of the sensor is about 250cm).
(v) With the correct materials chosen, the sensor
should offer a much higher strain-fatique
tolerance than strain gauges.
The results in Fig. 3 show the predicted attenuation (dB) against strain.
It can be seen that for small gauge-lengths the logarithmic response of the sensor is approximately linear with strain, but with large gauge-lengths the attenuation for a given strain is much larger. Some preliminary experiments have been performed with this sensor, and it was found that even the curing strain, and residual strain in an epoxy could be monitored during curing. This sensor could have a significant use for monitoring strain on structures, cure monitoring, and internal strain within 'smart structures'.
A 35 mm strain sensor has been fabricated and tested for low strain levels ( < 0.15a) which has shown excellent consistency with the predicted behaviour. The preliminary test results are shown in Fig. 4. It can be seen that there is only a slight deviation from the predicted data, but is so small as to be insignificant.
With respect to manufacturing these sensors, the methodology is proposed as shown in Fig. 5. This involves embedding a 'pre-notched' fibre within the material before embedding. Post-embedding the component is subjected to an appropriate defined radius of curvature, or subjected to a pre-defined tensile stress: this propagates the notch to give two cleaved faces.
The behaviour of this sensor is then as described above.
With the appropriate selection of materials used in the construction of the sensor the major measurand becomes temperature. The critical components for temperature monitoring will be the precision bore fixture and the optical fibres. In order to maximise sensitivity to temperature the precision bore fixture will have to be constructed from a material with a high coefficient of thermal expansion, and the fibres must have a much smaller coefficient.
As the temperature of the precision bore fixture increases, the fixture will deform leading to a separation of the fibre ends. This separation causes a greater loss of light within the sensor which can be related to the temperature of the fixture experimentally and analytically.
When a temperature sensor is to be used on (or within) a material that will undergo strain, a second sensor sensitised to strain will have to be employed to allow correction for the strain effect on the temperature sensor.
As with the case of the strain sensor it would be relatively simple to embed the sensor within a structure due to the very small dimensions of the complete assembly that can be achieved, with the resolution only limited by the length of the precision bore fixture.
A vibration sensor that could be easily fabricated from a very similar design to the strain sensor is shown in
Fig. 6. The mode of operation relies on the clearance between the precision bore fixture and the optical fibre being larger than with a strain sensor. The fibres are again fixed into place within the fixture, taking care that a pre-determined length of the fibre is free to oscillate as shown by the arrows within the clearance of the precision fixture.
The mechanical assembly follows the movements of the host material, but the unfixed ends of the fibres follow behind with a slight lag, causing bending of the fibres.
This bending ensures that only when the fibres are parallel is there a minimum attenuation of signal with increasing attenuation as the regular misalignment of the two fibres increases.
The period (or frequency) of oscillation can thus be measured via a gated timer-counter connected to a photodetector measuring the transmitted light intensity.
This can be quite inexpensively achieved using commercially available counter and operational amplifier integrated circuits.
The sensitivity of this sensor is governed by the amount of unbonded 'free' fibre and clearance with the precision bore, and could easily be 'tuned' to a specific application by varying these parameters for a given fibre type.
This sensor could quite easily be used for material (non-destructive) damage analysis by using it to monitor the natural frequency of the material being tested.
This can be used to detect cracking and fatigue damage etc. within materials. this can be achieved by inducing the material to vibrate and then monitoring the acoustic vibrations. Not only could the sensor be mounted onto the material, but could also be embedded a the time of manufacture so that continuous diagnosis might be achieved.
A proposed cure monitoring sensor is outlined in Fig. 7.
This sensor relies on changing the acceptance cone of the optic fibre via a change in refractive index in the media between the two fibre faces. For a fixed separation of the fibre ends, as the refractive index of the intermediary material varies so does the angle of acceptance for the fibre in that material. As the angle decreases, the corresponding attenuation of the sensor decreases because more light is transmitted into the second fibre.
By fabricating a sensor with a known separation of fibre ends, and with a 'v-groove' in the precision bore fixture, an intermediary uncured light transmissive material may be introduced between the fibre ends. If this sensor were to be embedded within a material to undergo curing, the material would flow into the groove and between the fibre-end. As the material cures, its refractive index will alter causing a corresponding change in attenuation, and thereby the cure may be monitored.
In most of these devices, the relationship between displacement of the fibres and change in measurand is governed by the gauge factor of the proposed sensors.
This gauge factor is predominantly defined by the gauge length of the sensor which fixes the relationship between the deformation of the outer tube to the displacement of the fibres.
The cure monitoring sensor is not a form of displacement sensor, but relies on the change of optical refractive index during curing of materials. The displacement for the fibres in this sensor is thereby fixed at the time of manufacture.
The vibration sensor is a form of lateral displacement sensor. The lateral displacements during vibration lead to an oscillating optical signal the frequency of which can be monitored using a frequency counter. The longitudinal displacement of the optical fibres is however irrelevant for this sensor.
An alternative technique of mounting the optical fibres in the tube relies on fusing the outer glass tube to the inner glass fibre to fix the gauge length.
Claims (15)
1. A sensor comprising a channel device which is in two discontinuous parts which can transmit radiation along the channel device when said parts are closely adjacent, and a measuring device which measures the variation of the radiation received when one part is displaced relative to the other, the attenuation being a measure of the amount of the displacement.
2. A sensor according to claim 1, wherein the channel device comprises an optical fibre including first and second facing fibre ends, the measuring device being coupled so as to measure the radiation received at the second fibre end, the first and second fibre ends being fixed in a bore of a housing.
3. A sensor according to claim 2, wherein the housing is resilient so as to expand or contract when stress is applied thereto, thereby to alter the spacing between the first and second fibre ends.
4. A sensor according to claim 2 or 3, wherein the housing has a predetermined coefficient of thermal expansion so as to expand or contract with changes in ambient temperature, thereby to alter the spacing between the first and second fibre ends.
5. A sensor according to claim 4, wherein the coefficient of expansion of the housing is high relative to that of the fibre.
6. A sensor according to any one of claims 2 to 5, wherein at least one of the first and second fibre ends is spaced from the bore of the housing and movable in a direction transverse to the axis of the bore.
7. A sensor according to any one of claims 2 to 6, wherein the first and second fibre ends are spaced from one another, a material being disposed in the space between the fibre ends, the material having an index of refraction able to change, thereby to change the angle of acceptance for the fibre and the amount of radiation received by the second fibre end.
8. A sensor according to claim 7, wherein the housing includes an aperture which communicates with the space between the first and second fibre ends, enabling material to pass into the space, the index of refraction of the material changing during curing thereof.
9. A method of making a sensor according to claim 2, comprising the steps of embedding the optical fibre in the housing and applying a tensile stress to ends of the fibre extending out of the housing so as to cleave the fibre within the housing to form the first and second facing fibre ends.
10. A method according to claim 9, comprising the step of making a notch in the fibre before embedding the fibre into the housing.
11. A method according to claim 9 or 10, wherein the tensile stress is applied to the fibre by bending the housing.
12. A method of making a sensor according to claim 2, comprising the steps of cleaving an optical fibre so as to provide first and second fibre ends, disposing the first and second fibre ends in facing relationship, and fusing a housing over the first and second fibre ends.
13. A method according to claim 12, wherein the first and second fibre ends are disposed at a predetermined spacing from one another prior to fusing the housing thereover.
14. A sensor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
15. A method of making a sensor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB939322352A GB9322352D0 (en) | 1993-10-29 | 1993-10-29 | Sensor device |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9421832D0 GB9421832D0 (en) | 1994-12-14 |
| GB2283567A true GB2283567A (en) | 1995-05-10 |
| GB2283567B GB2283567B (en) | 1998-03-18 |
Family
ID=10744342
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB939322352A Pending GB9322352D0 (en) | 1993-10-29 | 1993-10-29 | Sensor device |
| GB9421832A Expired - Fee Related GB2283567B (en) | 1993-10-29 | 1994-10-28 | Optical sensor device |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB939322352A Pending GB9322352D0 (en) | 1993-10-29 | 1993-10-29 | Sensor device |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB9322352D0 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001033179A1 (en) * | 1999-11-03 | 2001-05-10 | Vestas Wind Systems A/S | Method of manufacturing a fibre-optical strain-gauge and strain-gauge manufactured by said method |
| WO2002052223A1 (en) * | 2000-12-22 | 2002-07-04 | Vestas Wind Systems A/S | Fibre-optical strain gauge and method for the production of said strain gauge |
| WO2005047814A1 (en) * | 2003-10-17 | 2005-05-26 | Bed-Check Corporation | Displacement sensor apparatus |
| US7319400B2 (en) | 2003-10-17 | 2008-01-15 | Bed-Check Corporation | Method and apparatus for monitoring a restraint device |
| WO2009053717A2 (en) * | 2007-10-26 | 2009-04-30 | The University Of Birmingham | Sensor element |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4414471A (en) * | 1980-11-24 | 1983-11-08 | Sanders Associates, Inc. | Fiber optic acoustic signal transducer using reflector |
| US4421384A (en) * | 1979-08-03 | 1983-12-20 | Sperry Corporation | Fiber optic transducer |
| WO1987000920A1 (en) * | 1985-08-06 | 1987-02-12 | Optex Biomedical, Inc. | Fiber optic probe for quantification of colorimetric reactions |
| EP0286419A2 (en) * | 1987-04-10 | 1988-10-12 | McMillan, Norman | Method and apparatus for analysing liquid properties |
| US5089697A (en) * | 1989-01-11 | 1992-02-18 | Prohaska Otto J | Fiber optic sensing device including pressure detection and human implantable construction |
| US5140155A (en) * | 1990-10-17 | 1992-08-18 | Edjewise Sensor Products, Inc. | Fiber optic sensor with dual condition-responsive beams |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4384203A (en) * | 1981-05-18 | 1983-05-17 | General Electric Company | Optical fiber angle position sensor |
-
1993
- 1993-10-29 GB GB939322352A patent/GB9322352D0/en active Pending
-
1994
- 1994-10-28 GB GB9421832A patent/GB2283567B/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4421384A (en) * | 1979-08-03 | 1983-12-20 | Sperry Corporation | Fiber optic transducer |
| US4414471A (en) * | 1980-11-24 | 1983-11-08 | Sanders Associates, Inc. | Fiber optic acoustic signal transducer using reflector |
| WO1987000920A1 (en) * | 1985-08-06 | 1987-02-12 | Optex Biomedical, Inc. | Fiber optic probe for quantification of colorimetric reactions |
| EP0286419A2 (en) * | 1987-04-10 | 1988-10-12 | McMillan, Norman | Method and apparatus for analysing liquid properties |
| US5089697A (en) * | 1989-01-11 | 1992-02-18 | Prohaska Otto J | Fiber optic sensing device including pressure detection and human implantable construction |
| US5140155A (en) * | 1990-10-17 | 1992-08-18 | Edjewise Sensor Products, Inc. | Fiber optic sensor with dual condition-responsive beams |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001033179A1 (en) * | 1999-11-03 | 2001-05-10 | Vestas Wind Systems A/S | Method of manufacturing a fibre-optical strain-gauge and strain-gauge manufactured by said method |
| WO2002052223A1 (en) * | 2000-12-22 | 2002-07-04 | Vestas Wind Systems A/S | Fibre-optical strain gauge and method for the production of said strain gauge |
| WO2005047814A1 (en) * | 2003-10-17 | 2005-05-26 | Bed-Check Corporation | Displacement sensor apparatus |
| US7078676B2 (en) | 2003-10-17 | 2006-07-18 | Bed-Check Corporation | Displacement sensor apparatus |
| US7319400B2 (en) | 2003-10-17 | 2008-01-15 | Bed-Check Corporation | Method and apparatus for monitoring a restraint device |
| WO2009053717A2 (en) * | 2007-10-26 | 2009-04-30 | The University Of Birmingham | Sensor element |
| WO2009053717A3 (en) * | 2007-10-26 | 2009-09-24 | The University Of Birmingham | Sensor element |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9322352D0 (en) | 1993-12-15 |
| GB2283567B (en) | 1998-03-18 |
| GB9421832D0 (en) | 1994-12-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20041028 |