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Fiber optic evanescent wave sensor for ammonia gas

This article describes the design, development and characterization of an evanescent wave fiber optic sensor (EWFS) for the detection of toxic ammonia gas. Sol-gel technology is employed for immobilizing a reversible ammonia sensitive dye on the middle unclad region of a multimode fiber. Ammonia gas permeating into the immobilized dye, the color of the dye changes reversibly from yellow to blue with increasing concentration of ammonia gas. The concentration of ammonia gas can be determined by measuring the absorption at a given wavelength. The response of the sensor to different concentrations of ammonia, recovery time, reusability, etc of the developed sensor is also discussed. The techniques described here is also relevant to the detection of a wide range of other gases.