Optics: measuring and testing – Material strain analysis
Patent
1989-02-13
1991-01-08
McGraw, Vincent P.
Optics: measuring and testing
Material strain analysis
73800, 73802, 25022717, 356 33, G01B 1116
Patent
active
049830341
ABSTRACT:
An optical frequency domain distributed strain sensor for determining the strain distribution along an optical fiber includes an optical source that provides a polarization controlled optical interrogation signal having a frequency that varies in a recurring linear manner. The interrogation signal is injected into a sensor fiber embedded within a composite structure that places the fiber under strain. A portion of the interrogation signal is backscattered from the sensing fiber as a consequence of the strain experienced by the fiber and is mixed with a reference signal to produce beat frequency signals. The frequency of the beat signals is directly related the to position of backscatter in the sensing fiber while the amplitude of each beat frequency signal is directly related to the integrated strain-induced birefringence up to the backscatter point. An in-line fiber polarizer and an associated controllable polarizer control the polarization state of the interrogation signal in the sensor fiber to provide zero point sensitivity compensation and controllable testing for ambiguous strain points.
REFERENCES:
patent: 4692610 (1987-09-01), Szuchy
patent: 4836030 (1989-06-01), Martin
patent: 4840481 (1989-06-01), Spillman, Jr.
Kingsley et al., "OFDR Diagnostics for Fiber and Integrated-Optics Systems", Electronics Letters, 9 May 1985, vol. 21, No. 10, pp. 434-435.
Unsolicited Proposal for "An Investigation into Distributed Fiber Optic Strain Gauging Techniques for Composite Structure Monitoring", Hercules Aerospace Div., presented subsequent to Jan. 1, 1985 to NASA & Air Force.
Lovercheck Dale R.
McGraw Vincent P.
Simmonds Precision Products Inc.
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