We demonstrate the singlemode-multimode-singlemode (SMS) fiber structure for formalin detection. Formalin is a formaldehyde compound in water with an average concentration of 37 % and 15 % of methanol and water. Formalin consists of two substances; formaldehyde and water. Formaldehyde contamination in foods causes a negative effect for body. International Agency for Research on Cancer (IARC) classifies formaldehyde into Group 1 (carcinogenic to humans). Detection contamination of formalin in foods is very important. In this work, SMS fiber structure was used for formalin detection due to easy fabrication, cheap and more accurate in readings. This experiment utilized a difference in refractive index that affects the power output from optical fiber.
Conventional corrosion sensors such as ultrasonic guided waves, eddy current and thermography have been widely applied, however, these sensors have disadvantage of suffering from additional damage, as these sensors are placed in corrosive environment, often hidden and could not be directly observed, therefore corrosion inspection using conventional sensor is much more expensive and time consuming. Usage of optical fiber as corrosion sensor, based on changes in light intensity due to corrosion effect, is an alternative to overcome the disadvantage of conventional sensors. We proposed to use Single mode – Multimode Coreless – Single mode structured optical fiber as sensor. Multimode section of the optical fiber is coated with aluminium as the corrosion object. Experiment result shows that the corrosion process have an effect of decreasing the output sensor power as the corrosion rate increasing. Experimental test is conducted on the sensor, in which time interval of corrosion treatment is 9 hours. It is obtained from the test result that the highest value of output power is 13.19 dBm. Furthermore when the weight loss range of aluminium layer is 0 – 140 mg after corrosion treatment and the length of multimode fiber is 10 mm, the highest sensitivity of the sensor is 0.094 dBm/mg.
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