Distributed measurement of strain in smart materials using Rayleigh scattering

Rayleigh scattering is used to determine distributed strain along a single mode optical fiber. The technique consists of scanning a laser diode source to form an interference pattern between Rayleigh scattered light in the sensing fiber and a reference reflector. This pattern is then Fourier transformed to obtain the spatial distribution of Rayleigh scattering along the fiber. Changes in this distribution during sample loading are then interpreted in terms of strains along the fiber. The technique was demonstrated in several configurations, including beam bending in tension and compression, near a circular hole in a flat tensile specimen, and embedded in a graphite epoxy specimen. Strains up to 500 microstrain were obtained with a spatial resolution of 1 cm.