An Optical Fiber-Integrated Smart Structure for Flow Rate and Environmental Monitoring in Liquids

This article presents the development of a smart structure comprising a hydraulic metering arrangement for simultaneous data readings of temperature, flow rate, salinity, pH, and turbidity in liquids. The sensors are based on optical fiber sensing technologies following two major principles: fiber Bragg gratings (FBGs) and intensity variation-based sensors. The turbidity sensor is based on the light transmission between two distinct optic fiber cables, where the transmitted optical power is directly related to the turbidity of the medium. In addition, the FBG sensors are coated with different materials and placed at different positions to obtain the sensitivity of the desired parameters. Specifically, the salinity sensor is based on a polyimide-coated FBG, whereas the pH sensor uses a hydrogel-coated FBG. It is also worth noting that the FBGs are intrinsically sensitive to temperature and the FBG temperature sensor is based only on an uncoated FBG. Finally, the flow rate sensor is based on an FBG-embedded cantilever transversely positioned on the hydraulic section. All discussed sensors are embedded in a flanged hydraulic tube spool made by 3D-printing technology, and the data analysis and multiple output regression are based on the k-nearest neighbors (kNN) algorithm. The results show the feasibility of the proposed solution, where all developed sensors are able to detect the aforementioned parameters at different samples and different flow conditions. The relative errors of the sensors are below 3% considering the reference sensors used on samples’ preparation.