Polymer optical fiber grating as water activity sensor

Abstract

Controlling the water content within a product has long been required in the chemical processing, agriculture, food storage, paper manufacturing, semiconductor, pharmaceutical and fuel industries. The limitations of water content measurement as an indicator of safety and quality are attributed to differences in the strength with which water associates with other components in the product. Water activity indicates how tightly water is "bound," structurally or chemically, in products. Water absorption introduces changes in the volume and refractive index of poly(methyl methacrylate) PMMA. Therefore for a grating made in PMMA based optical fiber, its wavelength is an indicator of water absorption and PMMA thus can be used as a water activity sensor. In this work we have investigated the performance of a PMMA based optical fiber grating as a water activity sensor in sugar solution, saline solution and Jet A-1 aviation fuel. Samples of sugar solution with sugar concentration from 0 to 8%, saline solution with concentration from 0 to 22%, and dried (10ppm), ambient (39ppm) and wet (68ppm) aviation fuels were used in experiments. The corresponding water activities are measured as 1.0 to 0.99 for sugar solution, 1.0 to 0.86 for saline solution, and 0.15, 0.57 and 1.0 for the aviation fuel samples. The water content in the measured samples ranges from 100% (pure water) to 10 ppm (dried aviation fuel). The PMMA based optical fiber grating exhibits good sensitivity and consistent response, and Bragg wavelength shifts as large as 3.4 nm when the sensor is transferred from dry fuel to wet fuel.

Nearshore Contamination Monitoring in Sandy Soils Using Polymer Optical Fibre Bragg Grating Sensing Systems

“…Furthermore, the water affinity of PMMA can also be used to monitor the concentration of a solute dissolved in water, with the amount of water absorbed by the fibre determined by the concentration of the surrounding liquid. This has been demonstrated with both sugar and, most relevant to the current work, salt [ 38 ].…”

Time-dependent variation of POF Bragg grating reflectivity and wavelength submerged in different liquids

“…Furthermore, polyurethane 142 material has been successfully employed in our previous work [14] which shows good promise for 143 long term use in fuel. So, we also coated the entire fiber since PMMA material has affinity to water 144 [12,21].…”

“…Due to the moisture absorbing capability of PMMA based POFs, which leads to a 36 change in the refractive index and size of the fiber, both of which contribute to a change in Bragg 37 wavelength [6], these fibers are used to develop humidity sensors [ 8,11], water activity sensor in 38 fuels [7,12], among others. Although some significant research has been achieved in POF Bragg 39 gratings (POFBGs) including these applications, still some answers regarding the time-dependent 40 variation of optical properties in POFBGs remain unclear when they are placed in contact with water 41 and fuel.…”