Fiber-Optic Salinity Sensor Using Fiber-Optic Displacement Measurement With Flat and Concave Mirror

A simple intensity modulated displacement sensor is proposed for sensing salinity based on different concentration of sodium chloride (NaCl) in deionized water. The proposed sensor uses a 594-nm He-Ne laser as light source due to the high absorbance of NaCl within that wavelength. The peak voltage and its position of the displacement from both flat and concave mirror are studied. For a concentration change from 0% to 12%, the peak voltage decreases linearly from 2.46 to 1.48 mV, while its corresponding position from the flat mirror increases linearly from 1.00 to 1.35 mm with a linearity of more than 96% and 99%, respectively. Similarly, the peak voltage corresponding to the displacement with concave mirror decreases linearly from 3.67 to 3.57 mV, while its position increases linearly from 1.20 to 1.45 mm with a linearity of more than 98% and 95%, respectively. From the experimental results, it is concluded that as the concentration or density of NaCl increases, the peak voltage decreases proportionately. The stability, high sensitivity, simplicity of design, and low fabrication cost make this sensor suitable for chemical, pharmaceutical, biomedical, and process-control application.