Liquid-Level Measurement Using a Fabry–Perot Interferometer With a Transfer Mechanism

This article presents a novel liquid-level sensor that utilizes an extrinsic Fabry-Perot interferometer (EFPI), which is renowned for its exceptional dynamic range, sensitivity, and resolution. The sensor employs a distinctive transfer mechanism consisting of a cantilever beam and a floating configuration. By incorporating a circular mirror at the cantilever’s free end, along with a fiber end face and a 45° mirror, it establishes a variable cross-axial Fabry-Perot cavity. The floating configuration transduces and directs variations in liquid level to modulate the cavity length. Consequently, significant alterations in liquid level induce deflection of the cantilever beam, which can be quantified by analyzing the interference spectra of the EFPI. Initial calibration reveals that there is a linear relationship between changes in cavity length and alterations in liquid level. In experimental tests, this sensor achieved an impressive sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 1.192~\mu $ </tex-math></inline-formula>m/mm and achieves a resolution of 0.84 nm. Furthermore, it exhibits minimal temperature dependence with only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 6.508~\mu $ </tex-math></inline-formula>m/°C variation in liquid level within its full-scale range of 200 mm, indicating negligible impact from temperature fluctuations. The assessment for zero stability shows fluctuations in the liquid level amounting to only 0.002% of the full-scale range. With its simplicity, wide dynamic range, high sensitivity, prolonged fatigue life, and outstanding stability, this sensor holds great promise for challenging industrial environments, such as civil engineering, geotechnical engineering, and environmental monitoring.