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A Liquid-Level Sensor Based on a Hollow Coaxial Cable Fabry–Perot Resonator With Micrometer Resolution

For the first time, a hollow coaxial cable Fabry–Perot resonator (FPR)-based liquid-level sensor with centimeter dynamic range and micrometer resolution is proposed and demonstrated. The hollow coaxial cable, as the novel sensing platform, is homemade, in which air replaces the traditional dielectric layer. The FPR consists of two highly reflective reflectors, i.e., an artificial cylindrical steel bar and the air–liquid interface. The liquid level is directly transferred to the cavity length of the FPR, and the cavity length can be calculated by the resonant frequency/wavelength of the resonator. The experimental results show that our prototype liquid-level sensor has a sensitivity of 0.51 mm/mm (resonant wavelength change/liquid level) over a dynamic range of around 200 mm. The temperature dependence was also investigated. The novel liquid-level sensor, with high robustness, ease of fabrication, cost effective, wide dynamic range, and high resolution, is expected to have high potential applications in chemical industry, fuel storage, and water-level monitoring.