A novel multi-functional fibre optic sensor

Whilst considerable progress continues to be made on the design and deployment of fibre optic sensors for chemical process monitoring and structural integrity assessment, the majority of these sensor designs can only impart information on one or two relevant measurands. For example, in the case of chemical process monitoring of advanced fibrereinforced composites involving thermosetting resins, it is generally appreciated that cross-linking kinetics can be influenced by a number of factors including the following: the stoichiometry of the reagents, temperature, surface chemistry of the substrate and presence or absence of contaminants. Thermosetting resins also shrink during the crosslinking process. When thermosets are used and processed above room temperature during the production of fibrereinforced composites, upon cooling back to ambient temperature, residual stress can develop due to the mismatch in thermal expansions between the reinforcing fibres and the matrix. This paper reports on recent progress on the design and demonstration of a novel multi-functional fibre optic sensor that can provide data on (i) temperature, (ii) strain, (iii) refractive index, (iv) transmission infrared spectroscopy and (v) evanescent wave spectroscopy. A unique and attractive feature of this sensor is that a conventional commercially available Fourier transform infrared spectrometer is used to interrogate the sensor. The sensor design is based on an extrinsic fibre Fabry-Perot interferometer.