US4421979A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Microbending of optical fibers for remote force measurement
Assignee: Northrop Grumman Space and Mission Systems Corp
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Filing: 1981-08-27
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Granted: 1983-12-20
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Expires: 2001-08-27
Abstract
Abstract A system for remote measurement of structural forces includes a plurality of microbend transducers mounted along the length of the structure for microbending an optical fiber in response to structural forces, such as stress acting upon an oil or gas pipeline or the like. An optical time domain reflectometer (OTDR) has a light source for launching a pulsed optical signal for passage through the fiber and a photodetector for sensing as a function of time the intensity of backscattered light reflected back through the fiber, wherein this sensed time function is correlated directly with discrete longitudinal positions along the length of the fiber and the structure. When one or more of the microbend transducers is activated to induce a microbend in the fiber in response to localized forces acting upon the structure, a portion of the backscattered light is lost at the microbend. This attenuation in backscattered light intensity is sensed quantitatively and positionally identified by the photodetector. Specific preferred constructions for microbend transducers and system arrangements particularly adapted for detecting structural strain in an oil or gas pipeline are disclosed.
Inventors
- 👤 Charles K. Asawa
- 👤 Shi-Kay Yao
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 15:39
CPC Classifications
G; G01; G01L; G01L1/00; G01L1/24; G01L1/242; G01L1/243; G01L1/245
Claims Analysis
Total Claims: 38
Claim 1
Independent Claim
178 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and position indicator means interposed between selected ones of said force transducers in operative association with said fiber for altering light transmissivity characteristics of said fiber, wherein the alteration of fiber transmissivity is detectable by said detecting means.
Claim 2
Independent Claim
178 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and position indicator means interposed between selected ones of said force transducers in operative association with said fiber for altering light transmissivity characteristics of said fiber, wherein the alteration of fiber transmissivity is detectable by said detecting means.
Claim 3
Dependent Claim
32 words
The system of claim 1 wherein said position indicating means comprises means for reflecting a detectable portion of the pulsed light signal back through the fiber for detection by said detecting means.
Claim 4
Dependent Claim
13 words
The system of claim 2 wherein said position indicating means comprises a coupler.
Claim 5
Dependent Claim
35 words
The system of claim 1 wherein said plurality of transducers are mounted on the structure in sets, and wherein said position indicating means are interposed between each of the transducers of each of said sets.
Claim 6
Dependent Claim
39 words
The system of claim 4 wherein each of said sets of transducers comprises a plurality of transducers mounted along the structure generally at a common longitudinal position for respective response to forces acting in different directions upon the structure.
Claim 7
Dependent Claim
19 words
The system of claim 1 wherein said means for launching said pulsed optical signal comprises a laser light source.
Claim 8
Dependent Claim
53 words
The system of claim 1 wherein said signal launching means comprises a light source and said detecting means comprises a photodetector, and including optical means positioned generally adjacent one end of said fiber for direction of said pulsed optical signal into said fiber and for direction of said backscattered light to said photodetector.
Claim 9
Dependent Claim
29 words
The system of claim 1 wherein at least one of said position indicator means comprises means for altering the light transmissivity characteristics of said fiber by a known magnitude.
Claim 10
Dependent Claim
29 words
The system of claim 8 wherein said at least one position indicator means comprises means for reflecting back through the fiber a predetermined portion of the pulsed light signal.
Claim 11
Dependent Claim
27 words
The system of claim 1 wherein said force transducers are mounted on the structure for response to forces acting in at least two directions upon the structure.
Claim 12
Dependent Claim
21 words
The system of claim 1 wherein said signal launching means and said detecting means are positioned at a common monitoring station.
Claim 13
Independent Claim
142 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough whereby said signal is abruptly attenuated at each microbend in said fiber; means for detecting the amplitude and longitudinal position of each microbend in said fiber; and position indicator means interposed between selected ones of said force transducers for detectably altering the light transmissivity characteristics of said fiber to provide a reference for use in identifying which of said transducers is inducing microbending of said fiber.
Claim 14
Independent Claim
142 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough whereby said signal is abruptly attenuated at each microbend in said fiber; means for detecting the amplitude and longitudinal position of each microbend in said fiber; and position indicator means interposed between selected ones of said force transducers for detectably altering the light transmissivity characteristics of said fiber to provide a reference for use in identifying which of said transducers is inducing microbending of said fiber.
Claim 15
Dependent Claim
102 words
The system of claim 12 wherein a portion of said signal is reflected back through the fiber as backscattered light, said detecting means comprising a photodetector for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber, said position indicating means comprising means for reflecting a portion of the pulsed light signal back through said fiber to create a reflective spike detectable by said detecting means.
Claim 16
Dependent Claim
13 words
The system of claim 13 wherein said position indicating means comprises a coupler.
Claim 17
Dependent Claim
35 words
The system of claim 13 wherein said plurality of transducers are mounted on the structure in sets, and wherein said position indicating means are interposed between each of the transducers of each of said sets.
Claim 18
Dependent Claim
26 words
The system of claim 13 wherein said position indicator means comprises means for reflecting back through the fiber a predetermined portion of the pulsed light signal.
Claim 19
Dependent Claim
27 words
The system of claim 12 wherein said selected ones of said transducers are mounted on the structure for detecting forces acting in different directions on the structure.
Claim 20
Dependent Claim
31 words
The system of claim 12 wherein the structure comprises a pipeline, and wherein said force transducers are mounted on said pipeline for movement in response to stress acting on said pipeline.
Claim 21
Independent Claim
181 words
A system for monitoring force acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and means interposed between selected ones of said force transducers for reflecting back through said fiber a portion of the pulsed light signal to provide a reference for use in indicating which of said transducers is inducing microbending of said fiber.
Claim 22
Independent Claim
181 words
A system for monitoring force acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and means interposed between selected ones of said force transducers for reflecting back through said fiber a portion of the pulsed light signal to provide a reference for use in indicating which of said transducers is inducing microbending of said fiber.
Claim 23
Dependent Claim
12 words
The system of claim 19 wherein said reflecting means comprises a coupler.
Claim 24
Dependent Claim
27 words
The system of claim 19 wherein said selected ones of said transducers are mounted on the structure for detecting forces acting in different directions on the structure.
Claim 25
Dependent Claim
25 words
The system of claim 19 wherein said reflecting means comprises means for reflecting back through the fiber a predetermined portion of the pulsed light signal.
Claim 26
Independent Claim
178 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and means operatively associated with said fiber at a selected location along the length thereof for altering in a predetermined magnitude the light transmissivity characteristics of said fiber, wherein the transmissivity alteration is detectable by said detecting means.
Claim 27
Independent Claim
178 words
A system for monitoring forces acting upon a structure, comprising: an optical fiber extending along the structure; a plurality of force transducers each operatively associated with said fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; means for launching a pulsed optical signal into said fiber for passage therethrough and for reflection of a portion of said signal back through the fiber as backscattered light; means for detecting the intensity of said backscattered light as a function of time of reflection whereby each microbend along said fiber is indicated by an abrupt attenuation in said detected intensity and the time of detection is indicative of the location of the microbend along said fiber; and means operatively associated with said fiber at a selected location along the length thereof for altering in a predetermined magnitude the light transmissivity characteristics of said fiber, wherein the transmissivity alteration is detectable by said detecting means.
Claim 28
Dependent Claim
39 words
The system of claim 23 wherein said transmissivity altering means comprises means for reflecting back through the fiber a predetermined portion of the pulsed light signal to create a reflective spike of predetermined magnitude detectable by said detecting means.
Claim 29
Independent Claim
179 words
A method of monitoring forces acting upon a structure, comprising the steps of: providing an optical fiber to extend along the structure; mounting a plurality of force transducers each in operative association with the fiber on the structure for movement in response to a force acting on the structure to induce microbending of the fiber whereby light passing through the fiber is abruptly attenuated at each microbend therein; launching a pulsed optical signal into the fiber for passage therethrough and for reflection of a portion of the signal back through the fiber as backscattered light; detecting with detecting means the intensity of the backscattered light as a function of time of reflection whereby each microbend along the fiber is indicated by an abrupt attenuation in the detected intensity and the time of detection is indicative of the location of the microbend along the fiber; and altering the light transmissivity characteristics of said fiber between selected ones of the force transducers for detection by the detecting means to provide an indication of which transducer is inducing microbending of the fiber.
Claim 30
Independent Claim
179 words
A method of monitoring forces acting upon a structure, comprising the steps of: providing an optical fiber to extend along the structure; mounting a plurality of force transducers each in operative association with the fiber on the structure for movement in response to a force acting on the structure to induce microbending of the fiber whereby light passing through the fiber is abruptly attenuated at each microbend therein; launching a pulsed optical signal into the fiber for passage therethrough and for reflection of a portion of the signal back through the fiber as backscattered light; detecting with detecting means the intensity of the backscattered light as a function of time of reflection whereby each microbend along the fiber is indicated by an abrupt attenuation in the detected intensity and the time of detection is indicative of the location of the microbend along the fiber; and altering the light transmissivity characteristics of said fiber between selected ones of the force transducers for detection by the detecting means to provide an indication of which transducer is inducing microbending of the fiber.
Claim 31
Dependent Claim
22 words
The method of claim 25 wherein said altering step comprises reflecting a portion of the pulsed light signal back through the fiber.
Claim 32
Dependent Claim
23 words
The method of claim 25 wherein said altering step comprises reflecting a predetermined portion of the pulsed light signal back through the fiber.
Claim 33
Dependent Claim
35 words
The method of claim 25 including mounting the transducers in sets on the structure, and altering the light transmissivity of the fiber at a location between each of the transducers of each set of transducers.
Claim 34
Dependent Claim
28 words
The method of claim 28 including mounting the transducers of each set of transducers on the structure for response to forces acting in different directions upon the structure.
Claim 35
Dependent Claim
24 words
The method of claim 25 including mounting the selected ones of the transducers for response to forces acting in different directions upon the structure.
Claim 36
Independent Claim
190 words
A method of monitoring forces acting upon a structure, comprising the steps of: providing an optical fiber to extend along the structure; mounting a plurality of force transducers each in operative association with the fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of the fiber whereby light passing through the fiber is abruptly attenuated at each microbend therein; launching a pulsed optical signal into the fiber for passage therethrough and for reflection of a portion of the signal back through the fiber as backscattered light; detecting with detecting means the intensity of the backscattered light as a function of time of reflection whereby each microbend along the fiber is indicated by an abrupt attenuation in the detected intensity and the time of detection is indicative of the location of the microbend along the fiber; and altering the light transmissivity characteristics of the fiber at a selected location along the length thereof by a known magnitude for detection by the detecting means to provide a reference for comparison with the magnitude of attenuation at each microbend along the fiber.
Claim 37
Independent Claim
190 words
A method of monitoring forces acting upon a structure, comprising the steps of: providing an optical fiber to extend along the structure; mounting a plurality of force transducers each in operative association with the fiber and mounted on the structure for movement in response to a force acting on the structure to induce microbending of the fiber whereby light passing through the fiber is abruptly attenuated at each microbend therein; launching a pulsed optical signal into the fiber for passage therethrough and for reflection of a portion of the signal back through the fiber as backscattered light; detecting with detecting means the intensity of the backscattered light as a function of time of reflection whereby each microbend along the fiber is indicated by an abrupt attenuation in the detected intensity and the time of detection is indicative of the location of the microbend along the fiber; and altering the light transmissivity characteristics of the fiber at a selected location along the length thereof by a known magnitude for detection by the detecting means to provide a reference for comparison with the magnitude of attenuation at each microbend along the fiber.
Claim 38
Dependent Claim
23 words
The system of claim 31 wherein said altering step comprises reflecting a predetermined portion of the pulsed light signal back through the fiber.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-12-19 | 1987-06-20 | 1987-12-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-12-19 | 1991-06-20 | 1991-12-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-12-19 | 1995-06-20 | 1995-12-20 | $7700.00 | Window Closed / Lapsed |