Impact detection techniques are developed for application in the aerospace and defence
industries. Optical fibre sensors hold great promise for structural health monitoring
systems and methods of interrogating fibre Bragg gratings (FBG) are investigated given
the need for dynamic strain capture and multiplexed sensors.
An arrayed waveguide grating based interrogator is developed. The relationships
between key performance indicators, such as strain range and linearity of response, and
parameters such as the FBG length and spectral width are determined. It was found
that the inclusion of a semiconductor optical amplifier could increase the signal-to-noise
ratio by ~300% as the system moves to its least sensitive. An alternative interrogator is
investigated utilising two wave mixing in erbium-doped fibre in order to create an
adaptive system insensitive to quasistatic strain and temperature drifts. Dynamic strain
sensing was demonstrated at 200 Hz which remained functional while undergoing a
temperature shift of 8.5 °C.
In addition, software techniques are investigated for locating impact events on a curved
composite structure using both time-of-flight triangulation and neural networks. A
feature characteristic of composite damage creation is identified in dynamic signals
captured during impact. An algorithm is developed which successfully distinguishes
between signals characteristic of a non-damaging impact with those from a damaging
impact with a classification accuracy of 93 – 96%.
Finally, a demonstrator system is produced to exhibit some of the techniques developed
in this thesis
