From Event: SPIE Commercial + Scientific Sensing and Imaging, 2018
Rapid, accurate, and real-time measurements of ocean salinity are of great importance for a host of scientific, commercial and defense applications. We demonstrate a highly sensitive, fast-responding fiber-optic salinity sensor that integrates long-period fiber gratings (LPFG) with ionic strength-responsive hydrogel. Submicron-thick hydrogels were synthesized via layer-by-layer (LbL) assembly of partially quaternized poly(4-vinyl pyridine) (qP4VP) and poly(acrylic acid) (PAA), followed by chemical crosslinking of qP4VP and removal of PAA. Spectroscopic ellipsometry studies of hydrogels with 37% quaternized qP4VP revealed robust and reversible swelling/deswelling behavior of the coatings in solutions with different salt concentrations at pH 7.5. The performance of hydrogel-coated LPFG for the monitoring of sodium chloride solution in the salinity relevant range of 0.4 to 0.8 M was investigated. The swelling/deswelling process induced remarkable changes in the refractive index of the coating, resulting in robust shift in the resonance wavelength of LPFG. The hydrogel-coated LPFG exhibited a sensitivity of 7 nm/M with a response time less than 1 second. There is a linear correlation between the resonance wavelength shift and the salt concentration, making quantification of measured salinity straightforward.
Fan Yang, Raman Hlushko, Di Wu, Svetlana Sukhishvili, Henry Du, and Fei Tian, "Fast ocean salinity sensing based on long-period fiber gratings integrated with ionic strength-responsive hydrogel (Conference Presentation)," Proc. SPIE 10654, Fiber Optic Sensors and Applications XV, 106540Q (Presented at SPIE Commercial + Scientific Sensing and Imaging: April 18, 2018; Published: 14 May 2018); https://doi.org/10.1117/12.2304817.5783312845001.
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