Method and system for detecting dynamic strain
AssigneeHifi Engineering Inc.
InventorsJohn Hull, Seyed Ehsan Jalilian
Life of this patent
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Abstract
A system and method for detecting dynamic strain of a housing. The system includes an optical fiber linearly affixed along a surface of a length of the housing and an interrogator comprising a laser source and a photodetector. The optical fiber comprises at least one pair of fiber Bragg gratings (FBGs) tuned to reflect substantially identical wavelengths with a segment of the optical fiber extending between the FBGs. The segment of the optical fiber is linearly affixed along the surface of the housing. The interrogator is configured to perform interferometry by shining laser light along the optical fiber and detecting light reflected by the FBGs. The interrogator outputs dynamic strain measurements based on interferometry performed on the reflected light.
Claims18
A method for detecting dynamic strain of a housing, comprising:
- (a) shining laser light along an optical fiber buried in the ground without touching the housing to detect dynamic strain of the housing, wherein the optical fiber comprises at least one pair of fiber Bragg gratings (FBGs) tuned to reflect substantially identical wavelengths with a first segment of the optical fiber extending entirely linearly between the at least one pair of FBGs;
- and
- (b) detecting light reflected by the at least one pair of FBGs and performing interferometry on the reflected light to produce dynamic strain measurements based on the interferometry,
- wherein shining the laser light comprises shining a reference light pulse and a sensing light pulse along the optical fiber, the reference light pulse being delayed compared to the sensing light pulse by a predetermined period of time selected such that the reference light pulse reflected by a first FBG of the at least one pair of FBGs interferes with the sensing light pulse reflected by a second FBG of the at least one pair of FBGs to form a combined interference pulse, and wherein detecting the light reflected by the at least one pair of FBGs and performing the interferometry comprise detecting the combined interference pulse and detecting a phase difference between the reflected reference light pulse and the reflected sensing light pulse of the combined interference pulse to produce the dynamic strain measurements.
A system for detecting dynamic strain of a housing, the system comprising:
- (a) an optical fiber comprising at least one pair of fiber Bragg gratings (FBGs), wherein a first segment of the optical fiber extends entirely linearly between the at least one pair of FBGs and wherein the at least one pair of FBGs are tuned to reflect a first wavelength of laser light;
- (b) the housing;
- (c) earth surrounding the optical fiber and the housing such that the optical fiber is not in contact with the housing;
- and
- (d) an interrogator comprising a laser source and a photodetector, wherein the interrogator is configured to perform interferometry based on a phase difference resulting from a change in an optical path length between a first FBG and a second FBG of the at least one pair of FBGs by shining laser light at the first wavelength along the optical fiber and detecting light reflected by the at least one pair of FBGs, and wherein the interrogator outputs dynamic strain measurements based on interferometry performed on the reflected light,
- wherein the interrogator is configured to:
- (i) shine a reference light pulse and a sensing light pulse along the optical fiber, the reference light pulse being delayed compared to the sensing light pulse by a predetermined period of time selected such that the reference light pulse reflected by the first FBG of the at least one pair of FBGs interferes with the sensing light pulse reflected by the second FBG of the at least one pair of FBGs to form a combined interference pulse;
- (ii) detect the combined interference pulse;
- and
- (iii) detect as the phase difference a difference in phase between the reflected reference light pulse and the reflected sensing light pulse of the combined interference pulse to produce the dynamic strain measurements.
Dependencies are inferred from the claim text.