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12 July 1993 Optical fiber sensors for measurement of strain and acoustic waves
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A surface acoustic wave (SAW) sensor based on an extrinsic Fabry-Perot interferometer is described. A single-mode fiber, used as the input/output fiber, and a multimode fiber, used solely as a reflector, form an air-gap that acts as a low-finesse Fabry-Perot cavity. The Fresnel reference reflection from the glass/air interface at the front of the air-gap interferes with the sensing reflection from the air/glass interface at the far end of the air-gap. Strains in the silica tube housing the two fibers change the air-gap length, thereby altering the phase difference between the reference and sensing reflections. A theoretical analysis of the interaction between the strain induced by elastic stress wave fields and the fiber sensor is presented. A dual optical wavelength stabilization technique is used to minimize signal drifts. Signal to noise ratios on the order of 39 dB are obtained with a sensitivity of 4 degree(s)/microsecond(s) train cm-1 for strain measurements. The sensor was also attached to a steel cantilever beam and submerged in liquid nitrogen. The sensor was used to measure strain at liquid nitrogen temperatures with typical errors of less than 10%.
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Kent A. Murphy, Michael F. Gunther, Richard O. Claus, Tuan A. Tran, and Mark S. Miller "Optical fiber sensors for measurement of strain and acoustic waves", Proc. SPIE 1918, Smart Structures and Materials 1993: Smart Sensing, Processing, and Instrumentation, (12 July 1993);

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