Abstract
In this paper, a new optical fiber corrosion sensor based on metallic bilayers is described. The detection region is located at a fiber end facet and we present simulations as well as experimental results in controlled lab conditions for Ti(10 nm)/Al(10 nm) and Ni(5 nm)/Al(5 nm) bilayers. We perform the characterization of the device by numerical simulations using the COMSOL Multiphysics software, and with an analytical model, which makes use of the Fresnel equations. According to the simulations, the change in the reflected optical signal over time is related to variations in the thickness of the metallic films by the corrosive process and, consequently, the corrosion rate in each metal of the bilayer can be obtained. Upon the simulation results, sensor devices were fabricated by depositing thin metallic films on the cleaved facet of the optical fiber using the sputtering method. We show that the use of a metallic bilayer as a transducer, instead of a monolayer, improves the sensor measuring interval (20 ± 1 nm) and provides information about the corrosion rate along the corrosion process.
Highlights
Corrosion is one of the main degradation mechanisms that affect industrial structures, whether they are static, such as bridges, gas pipes, oil pipelines, that normally operate in a highly corrosive environment, as well as mobile transport structures, such as ships or aircrafts [1]
The use of a bilayer, instead of a monolayer as in previous publications, improves the sensor measuring interval, mitigating the sensor blind period problem identified in monolayer structures, and provides the corrosion rate earlier during the corrosion process
Fig. 5 shows the results obtained from the COMSOL numerical model considering surface roughness, the analytical model of laminar corrosion from the Fresnel equations and the experimental results for the reflectance as a function of the thickness of the thin films deposited at the end of the fiber
Summary
Corrosion is one of the main degradation mechanisms that affect industrial structures, whether they are static, such as bridges, gas pipes, oil pipelines, that normally operate in a highly corrosive environment, as well as mobile transport structures, such as ships or aircrafts [1]. Sensing techniques based on optical fibers have advantages such as simplicity, versatility, safety, reliability, distributed measurement, immunity to external electromagnetic interference and ability to resist hostile environments. For this reason, some optical fiber sensors are commercially available [5], [6]. The use of fiber optics allows signals to be transmitted over long distances with low loss, enabling a remote monitoring system. As such, it is suitable for use in highly controlled environments such as nuclear or chemical plants [7]. Optical fiberbased sensors are used to monitor various physical and chemical properties such as humidity [8], microbends [9], [10], electric field [11], [12], temperature [13], [14], pressure [ 15], magnetic field [16], gas [17], [18], corrosion [19]-[21] among others
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