Design of fiber optic sensor systems for low velocity impact detection

This paper describes the design and development of promising optical fiber sensor systems for low velocity impact detection and impact-induced damage assessment. The sensor systems were based on the combination of path-matched differential interferometry (PMDI), in-line fiber etalon (ILFE) sensors and specifically designed analog phase trackers. The four demodulators investigated include: (1) the phase generated carrier (PGC) with differential-cross-multiplier (DCM) implemented electronically; (2) the PGC with DCM but where the final integration in the DCM is carried out numerically; (3) the single-channel phase tracker; and (4) the sin(Delta phi)/cos(Delta phi) phase tracker. Careful consideration is given to an impact sensor system design methodology that considers potential optical sensor configurations, dynamic range and bandwidth of demodulation systems, optical phase-strain relationships, and the mechanical interaction of the optical fiber with its host structure. initial impact tests using aluminium plates with surface-mounted ILFE sensors were performed to investigate the capability of the four given demodulators. The single-channel and sin(Delta phi)/cos(Delta phi) phase trackers proved to be most suitable for the present impact application, and therefore they were utilized in the low velocity impact tests using graphite/epoxy composite plates with embedded ILFE sensors.