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Embedded acoustic fibre waveguides for Lamb wave condition monitoring

This paper describes work aimed towards the realisation of an embedded ultrasonic monitoring system for operation in a smart structure environment. 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 on the coupling of ultrasound from the waveguide to the desired Lamb wave mode. Therefore, novel transducer designs for efficient single mode generation in the fibre waveguides are essential. 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. This paper presents work-to-date on the realisation of such an ultrasonic monitoring system.