Impact characterization by optical fiber ultrasonic sensors

The performance of optical fiber modal domain sensors for impact and damage detection in materials is discussed. A portion of stripped optical fiber having a V number of approximately 4.5 was attached to a thick aluminium plate with rigid epoxy. The fiber was excited with laser light and monitored with a photodetector. With the plate inverted and lying flat, for several trials a steel mass was dropped on the plate from various heights and positions with respect to the fiber sensor. Changes in the fiber modal pattern were captured over the course of an impact. Power densities were calculated and analyzed with respect to impact amplitude. Also, Fourier analysis of the signals allowed the correlation of spectral signatures with different types of impacts. After a second fiber was attached to the plate, similar drop tests were run, and impact location information was extracted by examining the time delay between the disturbance signals from the two fibers