Static-strain sensitivity optimization of fiber optic extrinsic Fabry-Perot interferometric strain gauge

摘要

Surface mounted optical fiber strain sensors have been extensively used in smart structure sensing and actuator applications in the recent past. The performance of such sensors depends strongly on the conditions of bonding. Optimum static strain sensitivity of an extrinsic fiber optic interferometric strain gauge surface mounted on a cantilever beam was obtained by comparing several bonding techniques to each other, by comparing the outputs of the fiber sensors and resistance foil gauges, and by comparing the strain calculated from applied end displacements and elastic beam theory. The extrinsic fiber interferometer was formed between the ends of a single mode fiber (SMF) and a multimode fiber (MMF) inserted into a hollow core fiber (HCF) from opposite ends. Resistance foil and optical interferometric measurements were consistently lower than theoretical values. The closest agreement with theoretical values was realized by a configuration in which the SMF end was free to move within the HCF. For a sensor completely embedded in epoxy, optical strain measurements were 12.2% below theoretical values while the foil gauge readout was 18.1% lower.