Developing a Planar Three Dimensional Fiber Optic Strain Sensor Array

A planar fiber optic strain sensor array capable of measuring three dimensional (3-D) strains inside a material has been developed. Three dimensional strain measurement is an emerging technology that can be used in a variety of applications including composite structures, sensing for adaptive structures, intelligent vehicle highway systems and health monitoring systems for civil structures. A planar array was developed to avoid the difficulty and structural degradation of embedding optical sensors in three planes. Two extrinsic Fabry-Perot Interferometric sensors (EFPIs) and one polarimetric sensor were used to form the planar sensor array. The two EFPIs were placed perpendicular to each other in the same plane to extract two normal strain components along the x and y axes. A polarimetric sensor was embedded in the same plane to extract the third normal strain acting on the z axis. This sensor array was embedded in an epoxy resin cube. An external load of 1000 pounds was applied with a loading machine. The measured strains from the embedded optical fiber sensors correlated well with the external strains measured with surface bonded electrical strain gauges. The variation in measured strain between the two sensor systems was less than 3.5% on all three principal axes.