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Coated FBG Sensor With Enhanced Temperature Sensitivity for Cryogenic Liquid-Level Detection
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DOI：10.1109/jsen.2026.3705743.png)
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Abstract
En 中文
A cryogenic liquid-level sensor based on fiber Bragg grating (FBG) was proposed. The sensor measures the liquid-level height by transmitting the liquid pressure through a stainless steel elastic diaphragm, which changes the central wavelength of the FBG. The influence of liquid nitrogen temperature changes on liquid-level measurement is compensated by using the reference grating method, and the sensitivity of the temperature-compensated grating is enhanced through coating technology. The elastic diaphragm, which serves as the sensor’s sensitive element, is designed based on finite element analysis, with a thickness of 0.03 mm and a diameter of 84 mm. Based on the theories of FBG sensing and material mechanics, the effects of plating thickness and other factors on the temperature sensitivity of the FBG are analyzed. Three FBG sensors coated with nickel, gold, and polyimide were fabricated using chemical methods, magnetron sputtering, and coating techniques. The performance of the coated FBG was experimentally verified. The gold-coated FBG had the highest temperature sensitivity, thus serving as a temperature compensation grating. Through the sensor temperature testing experiment, the temperature sensitivities of the temperature compensation grating and the liquid-level measurement grating were determined to be 8.14 and 1.214 pm/°C, respectively. The liquid-level measurement formula after compensation for temperature was derived. Cryogenic liquid-level sensing experiments demonstrate that the sensor has a liquid nitrogen level sensitivity of 0.051 nm/m, a measurement range of 0–0.5 m, and a maximum relative error of 1.96%.
Keywords:
Elastic membrane
fiber Bragg grating (FBG)
fiber coating
liquid-level measurement
liquid nitrogen
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