SIMULATION OF FIBER OPTIC SENSORS IN DETERMINATION OF THIN LIQUID-FILM THICKNESSES

A two-dimensional simulation had been conducted to determine the thick ness and orientation of a clear thin liquid film for both the multi-fi ber and mono-fiber optic sensors developed recently. The multi-fiber s ensor consists of a central light emitting fiber which is surrounded s ymmetrically by six light receiving fibers while the mono-fiber sensor has only one fiber which acts as both the light emitting and receivin g sources. By analyzing the different patterns of light intensity refl ected back at the liquid surface and collected by the receiving fibers , the thin film thickness and its orientation with respect to the meas uring point can be determined. The present study suggests that the mul ti-fiber sensor is capable of measuring liquid thin film thicknesses, including orientation relative to the measuring point, within the rang e of 1-4 mm. Below the range of 1 mm, the use of mono-fiber sensor app ears to be more effective. In both cases, limitation is mainly imposed by the numerical aperture of the fiber used.