Active fibre waveguide sensor for embedded structural condition monitoring

Work aimed towards the realisation of an embedded ultrasonic system for structural condition monitoring is described. Alien fibres embedded within carbon fibre reinforced composite plates could be utilised to guide ultrasound to strategic release points for the interrogation of the test sample, with minimal structural degradation. In particular, an array of fibre waveguides could be utilised to deliver periodic stresses to a plate-type structure to excite Lamb wave propagation. With such a system several problems need to be addressed. Ideally, single mode propagation in the fibre waveguide is required to provide increased control of the coupling of ultrasound from the waveguide to the desired Lamb wave mode. The choice of a suitable waveguide material and geometry is also crucial to ensure the guided ultrasound does not leak into the structure at undesirable locations and that the structural integrity of the test sample is maintained. Consequently, various waveguide configurations are investigated to establish an arrangement capable of meeting the system requirements. Finally, So Lamb wave generation and detection in a hard-setting polymer plate and a carbon fibre reinforced composite plate is demonstrated utilising embedded active acoustic waveguides sensors.