Microbending of optical fibers for remote force measurement
First Claim
1. 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;
each of said force transducers comprising a relatively flexible beam mounted on the structure for movement therewith in response to a bending force acting upon the structure, a relatively rigid beam mounted in spaced, generally parallel relation with said flexible beam and the structure, and transducer block members carried respectively by said flexible and rigid beams in relatively closely spaced relation with each other and for relative movement toward each other upon movement of said flexible beam toward said rigid beam, said transducer block members including facing surfaces each having a generally irregular shaped profile, said optical fiber extending between said facing surfaces of said transducer block members, said facing surfaces being for engaging said fiber upon movement of said flexible beam toward said rigid beam to induce a microbend in said fiber for attenuation of a portion of the light propagated through said fiber at the microbend whereby a portion of the light is transmitted from the fiber at the microbend;
means for launching a pulsed optical signal into said fiber for passage therethrough and for substantially continuous reflection along the length of said fiber of a portion of said signal back through the fiber as backscattered light; and
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;
said signal launching means and said detecting means being positioned at a common monitoring station, said signal launching means comprising a light source and said detecting means comprising 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.
1 Assignment
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Accused Products
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.
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Citations
37 Claims
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1. A system for monitoring forces acting upon a structure, comprising:
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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; each of said force transducers comprising a relatively flexible beam mounted on the structure for movement therewith in response to a bending force acting upon the structure, a relatively rigid beam mounted in spaced, generally parallel relation with said flexible beam and the structure, and transducer block members carried respectively by said flexible and rigid beams in relatively closely spaced relation with each other and for relative movement toward each other upon movement of said flexible beam toward said rigid beam, said transducer block members including facing surfaces each having a generally irregular shaped profile, said optical fiber extending between said facing surfaces of said transducer block members, said facing surfaces being for engaging said fiber upon movement of said flexible beam toward said rigid beam to induce a microbend in said fiber for attenuation of a portion of the light propagated through said fiber at the microbend whereby a portion of the light is transmitted from the fiber at the microbend; means for launching a pulsed optical signal into said fiber for passage therethrough and for substantially continuous reflection along the length of said fiber of a portion of said signal back through the fiber as backscattered light; and 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; said signal launching means and said detecting means being positioned at a common monitoring station, said signal launching means comprising a light source and said detecting means comprising 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A system for monitoring forces acting upon a structure, comprising:
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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 stress acting on the structure to induce microbending of said fiber whereby light passing through said fiber is abruptly attenuated at each microbend therein; each of said force transducers comprising a first transducer member having one end secured at a first position along the structure for movement therewith in response to a force acting upon the structure and extending from said one end generally along the structure and terminating in a free end generally opposite said one end, a second transducer member secured at a second position along the structure for movement therewith in response to the force acting upon the structure, said first and second transducer members including relatively closely spaced facing surfaces each having a generally irregular shaped profile, said facing surfaces being movable relatively to each other in response to the force acting upon the structure, said optical fiber extending between said facing surfaces for engagement by said surfaces for microbending of said fiber in response to the force acting on the structure; means for launching a pulsed optical signal into said fiber for passage therethrough and for substantially continuous reflection along the length of said fiber of a portion of said signal back through the fiber as backscattered light; and 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; said signal launching means and said detecting means being positioned at a common monitoring station, said signal launching means comprising a light source and said detecting means comprising 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. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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30. A microbend transducer for use in detecting a force acting upon a structure, comprising:
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a cable having an optical fiber, a protective sheathing encasing said fiber, and an elongated wire wound spirally about said fiber with predetermined longitudinal spacing between turns and interposed between said fiber and said sheathing for inducing a microbend in said fiber in response to lateral compression of said cable; and force responsive means secured to the structure and operably associated with said cable for laterally compressing said cable in response to a force acting upon the structure to cause attenuation of light propagated through said fiber whereby a portion of the light is transmitted from the fiber at the microbend. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37)
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Specification