High resolution liquid level sensor based on Archimedes’ law of buoyancy using polymer optical fiber Bragg gratings

• First report of liquid level sensor based on Archimedes’ law of buoyancy with FBGs in POF. • High-sensitivity liquid level measurement, allowing resolutions as fine as 0.2 mm. • Improvement in sensitivity in approximately 21 times compared to the silica fiber sensor. • Capability to detect small leakages in large liquid reservoirs. In this paper, we present a polymer optical fiber (POF) Bragg grating (FBG) to measure liquid level based on Archimides’ law of buoyancy. The sensor consists of polymer 3D-printed rods with different radii attached to the fiber terminal containing an FBG. Characterization is performed by submerging the rods in a beaker containing water at different level heights. The tension force applied onto the optical fiber changes with the level of the liquid, which is then measured through the FBG. Considering the smaller Young’s modulus of the POF compared to that of a silica optical fiber, it is possible to induce larger strain changes, and thus, enhance the liquid level sensitivity. Our results show a liquid level sensitivity enhancement of up to ≈ 21 times when compared to the silica FBG. This enhancement enables liquid level resolution of 0.2 mm for the polymer FBG as opposed to 2.6 mm for the silica counterpart.