Remote process monitoring using optical fibre sensors

Conventional means of curing thermosetting resins used in advanced fibre reinforced composites involves heating the sample in an oven or autoclave where heat is transferred to the sample through conduction and convection. This conventional method for manufacturing composites involves long processing time. On the other hand, microwave-based processing offers the advantage of a significantly faster processing time where the heating occurs directly inside the sample. The use of microwave radiation however, necessitates the need for non-metallic cure monitoring systems. In this study, two remote (non-contact) sensor systems were designed and developed to facilitate spectral-based process monitoring inside a custom-modified commercial microwave oven. The two fibre optic sensor systems were (i) a non-contact optical fibre reflectance probe and (ii) a reusable transmission probe. Spectroscopic data were obtained using the fibre optic probes at specified microwave power levels. A low-cost temperature probe was developed in this current study and it was based on an optical fibre-based extrinsic Fabry-Perot interferometer (EFPI). The EFPI temperature sensor demonstrated an accuracy of ±1°C over the range from ambient to 300°C. The temperature of the resin system was also measured simultaneously along with the spectral data to monitor the progress of the chemical reaction (curing).