The use of a high-performance fiber optic measurement system in structural damage assessment

We have developed and tested a fiber optic system that relies on Fiber Bragg Gratings (FBGs) as strain gages for structural monitoring. FBGs reflect a narrow (< 0.2 nm) band of light whose center wavelength changes as the fiber is stretched or compressed. We interrogate multiple FBGs distributed along one strand of optical fiber with a scanning Fabry-Perot filter for selecting individual reflection wavelengths, an unbalanced Mach-Zehnder interferometer to detect wavelength shifts, and a 3×3 fiber optic coupler which converts the wavelength shifts into phase changes. This work will describe the system in detail, present key performance metrics, and demonstrate the use of the system in detection of boundary clamp damage in a chaotically excited beam. The features chosen in the damage assessment problem are based on subtle geometric changes which occur on the system attractor changes as the beam is damaged.