A novel sensing system based on single mode optical fiber in reflective configuration has been developed to measure the critical meniscus height (CMH) of low volumes of liquids, which is then used to calculate the contact angle. The sensing system has been designed especially for very low volumes of liquids (e.g. bio-liquids) and the work has demonstrated that measurements are possible with a minimum liquid volume of $5~\mu \text{L}$ . The sensing system is based on monitoring the spectral variation induced by the difference in the refractive index regions surrounding the fiber tip, at the air-liquid or liquid-liquid interfaces. From the experiments performed in water, (by immersing and extracting the fiber sensor in the liquid sample), it can be concluded that the CMH forming on the fiber decreases as the temperature increases. The change of temperature (in this experiment from 22 to 60 °) does not influence the CMH of the sample used in the evaluation (P3 mineral oil), giving an indication of its thermal stability. In addition, a fixed fiber was used to measure the variation in the liquid level when another fiber is immersed in the liquid. The error in the liquid level obtained in the work was small, at 0.34 ± 0.04 %. Such a sensor, allowing accurate measurements with very small quantities is especially useful where liquid sample volumes are limited e.g. biologically sourced liquids or specialized, expensive industrial material in the liquid phase.

中文翻译：

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使用光纤传感器监测极低液体体积的临界弯液面

已经开发了一种基于反射配置的单模光纤的新型传感系统，用于测量少量液体的临界弯液面高度 (CMH)，然后用于计算接触角。该传感系统专为极少量的液体（例如生物液体）而设计，工作表明，可以用 $5~\mu \text{L}$ 的最小液体体积进行测量。传感系统基于监测由光纤尖端周围、空气-液体或液体-液体界面处的折射率区域的差异引起的光谱变化。从在水中进行的实验（通过将光纤传感器浸入和提取到液体样品中）可以得出结论，在光纤上形成的 CMH 会随着温度的升高而减少。温度的变化（在本实验中从 22° 到 60°）不影响评估中使用的样品（P3 矿物油）的 CMH，表明其热稳定性。此外，当另一根光纤浸入液体中时，固定光纤用于测量液位的变化。工作中获得的液位误差很小，为 0.34 ± 0.04 %。这种允许以非常小的量进行精确测量的传感器在液体样品体积有限的情况下尤其有用，例如生物来源的液体或处于液相的专门的、昂贵的工业材料。当另一根光纤浸入液体中时，固定光纤用于测量液位的变化。工作中获得的液位误差很小，为 0.34 ± 0.04 %。这种允许以非常小的量进行精确测量的传感器在液体样品体积有限的情况下尤其有用，例如生物来源的液体或处于液相的专门的、昂贵的工业材料。当另一根光纤浸入液体中时，固定光纤用于测量液位的变化。工作中获得的液位误差很小，为 0.34 ± 0.04 %。这种允许以非常小的量进行精确测量的传感器在液体样品体积有限的情况下尤其有用，例如生物来源的液体或液相中的专门的、昂贵的工业材料。