This study focuses on the precise in situ online detection of moisture content in paper utilizing a tapered optical fiber evanescent wave sensor made from a polyvinyl alcohol/diatomite moisture-sensitive material and plastic optical fibers. We developed a theoretical model to detect the moisture content in paper based on the principle that a moisture-sensitive material expands upon absorbing water molecules, resulting in changes in its refractive index and altering the sensor's output optical signal. The experiment explored the impact of the fiber core diameter, cone angle, and moisture-sensitive film thickness on the sensor response characteristics. By incorporating a humidity reference unit, the study successfully eliminated interference from changes in ambient humidity on the measurement of the paper moisture content. Theoretical studies revealed that the sensor’s output signal is solely dependent on the moisture content of the paper and remains unaffected by fluctuations in ambient humidity. The sensitivity of the sensor is influenced by the thickness of the moisture-sensitive film, fiber core diameter, and cone angle. The sensor can accurately detect the paper's moisture content when the fiber core diameter is 2 mm, cone angle is 15 ± 0.5°, and moisture-sensitive film thickness is 90 μm, achieving a sensitivity of 0.1662 %/%ω and a maximum relative measurement error of less than 3 %. These findings have significant implications for the in situ online measurement of moisture content in solid substrates.

中文翻译：

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锥形光纤消逝波传感器，用于准确原位检测纸张水分含量


本研究的重点是利用由聚乙烯醇/硅藻土湿敏材料和塑料光纤制成的锥形光纤倏逝波传感器对纸张中的水分含量进行精确的原位在线检测。我们开发了一个理论模型来检测纸张中的水分含量，其原理是湿敏性材料在吸收水分子时膨胀，导致其折射率发生变化并改变传感器的输出光信号。该实验探讨了纤维芯径、锥角和湿敏性薄膜厚度对传感器响应特性的影响。通过结合湿度参考单元，该研究成功地消除了环境湿度变化对纸张水分含量测量的干扰。理论研究表明，传感器的输出信号完全取决于纸张的水分含量，不受环境湿度波动的影响。传感器的灵敏度受湿敏膜厚度、纤芯直径和锥角的影响。当纤维芯径为 2 mm，锥角为 15 ± 0.5°，湿敏膜厚度为 90 μm 时，该传感器可以准确检测纸张的水分含量，灵敏度为 0.1662 %/%ω，最大相对测量误差小于 3 %。这些发现对固体基材中水分含量的原位在线测量具有重要意义。