An evanescent wave fluorescence fiber optic flow sensor for resin transfer molding

An evanescent wave fluorescence based fiber optic flow sensor is being investigated. This sensor is based on the interaction of a laser beam in a bare optical fiber with fluorescent probe molecules present in the resin flowing in the direction of the fiber. The electric field of the monochromatic light waves traveling in the fiber by total internal reflection penetrates outside the fiber and is called the evanescent wave field. A fluorescent probe molecule within the depth of penetration gets excited by this field and emits a characteristic fluorescent radiation which is coupled back into the fiber by the principle of reciprocity of optics. If the light at the end of the fiber is filtered for the fluorescent radiation and the intensity is recorded, it gives an estimate of the number of fluorescent probe molecules in contact with the fiber and hence the extent to which the fiber is covered with the resin. Preliminary experiments have shown that there is a linear correlation between the peak intensity and the length of fiber in contact with the fluid. A laboratory set-up has been assembled at the University of Delaware using a photo-multiplier tube based detector and various experiments have been conducted to assess the effect of covered fiber length on the intensity of fluorescence using the evanescent mode of sensing and on the uses of distal mode sensing of fluorescence for detection of flow.