Measurement of chloride-ion concentration with long-period grating technology

Abstract

A simple and low-cost long-period fiber grating (LPG) sensor suited for chloride-ion concentration measurement is presented. The LPG sensor is found to be sensitive to the refractive index of the medium around the cladding surface of the sensing grating, thus offering the prospect of development of practical sensors such as an ambient index sensor or a chemical concentration indicator with high stability and reliability. We measured chloride ions in a typical concrete sample immersed in salt water solutions with different weight concentrations ranging from 0% to 25%. Results show that the LPG sensor exhibited a linear decrease in the transmission loss and resonance wavelength shift when the concentration increased. The measurement accuracy for the concentration of salt in water solution is estimated to be 0.6% and the limit of detection for chloride ions is about 0.04%. To further enhance its sensitivity for chloride concentrations, we coated a monolayer of colloidal gold nanoparticles as the active material on the grating surface of the LPG sensor. The operating principle of sensing is based on the sensitivity of localized surface plasmon resonance of self-assembled gold colloids on the grating section of the LPG. With this method, a factor of two increase in the sensitivity of detecting chemical solution concentrations was obtained. The advantages of this type of fiber-optic sensor are that it is compact, relatively simple to construct and easy to use. Moreover, the sensor has the potential capability for on-site, in vivo and remote sensing, and it has potential use as a disposable sensor.

Non-destructive measurement of chloride ions concentration in concrete – A comparative analysis of limitations and prospects

“…Embedded fiber optic chloride sensors allow a non-destructive manner of determining the Cl À content, along with Cl À penetration into concrete structures [71][72][73][74]. Over the last decade, several groups have developed fiber optic sensors to measure the free chloride content in concrete.…”

Threshold-based Energy Efficient Clustering Protocol for Corrosion Risk Monitoring of Reinforced Concrete

“…In [9], FOS has been used for monitoring the chloride penetration in a bridge spanning 67 m long. In [10][11][12][13][14], FOS has been used for chloride limit monitoring. Figure 1 shows corrosion in steel due to chloride attack [33].…”

Development of Novel Ceramic Nanofilm-Fiber Integrated Optical Sensors for Rapid Detection of Coal Derived Synthesis Gas

“…where n eff is the effective refractive index of the propagating guided mode, For a given LPFG with fixed fiber and grating parameters, the λ R undergoes a shift when the refractive index of the surrounding medium changes. Thus, LPFG-based sensors can be developed for direct or indirect measurement of chemical concentrations which determine the surrounding refractive index [47,48,49]. The sensitivity of a film-coated LPFG sensor depends on the comparison between the refractive indices of the overcoat (n ov ) and the fiber cladding (n cl ).…”