Evanescent wave optical fibre ammonia sensor with methylamine hydroiodide

A small portion of an optical fibre clad was removed and coated with methylamine hydroiodide by a slurry deposition process to develop an evanescent wave optical fibre ammonia sensor. The experiment was performed for a few volatile organic compounds in order to understand the selectivity and sensitivity. Prior to the gas sensing measurement, the methylamine hydroiodide sample was characterised using X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray spectroscopy, Fourier transform infrared, Raman, diffuse reflectance and UV-Vis spectroscopy. In order to understand the sensor response, the samples were independently exposed to acetone, ammonia, ethanol and methanol gases and then analysed using the XRD technique. This analysis reveals that the structural variation is observed because of the ammonia exposure as compared to other gases. It has initiated to fabricate a clad-modified optical fibre ammonia sensor that exhibits 28% of the sensitivity. These experimental results are discussed in detail.