Lupi Carla, Vendittozzi Cristian, Ciro Erwin, Felli Ferdinando
Dipartimento Ingegneria Chimica Materiali Ambiente, Sapienza Rome University, Via Eudossiana 18, 00184 Roma, Italy.
Campus FGA-UnB, Universidade de Brasília, Brasília 72444-240, DF, Brazil.
Sensors (Basel). 2022 Sep 24;22(19):7255. doi: 10.3390/s22197255.
FBG sensors are used in many scientific and industrial fields for assessing the structural integrity of mechanical components and in very high (above 600 °C) or very low (cryogenic) temperature applications. The main concerns with the use of such sensors in applications involving extreme temperatures are related partly to the instability of the reflected spectrum, which tends to dissolve into the noise floor, and partly to the degradation of the mechanical properties of the optical fiber, which tends to worsen the inherent brittleness. All of this raises the need for a robust nickel protective coating to ensure the grating's integrity in high-temperature environments. In addition, the inherent brittleness of fiber-optic gratings leaves one to wonder whether it is possible to recover a broken, seemingly unusable sensor. In this way, a single-peak commercial FBG was intentionally broken in the middle of the grating length and re-spliced, inducing a strongly asymmetric chirped-like spectrum; then, a nickel coating was electrodeposited on its surface. The most important outcome achieved by this work is the regeneration of a highly distorted reflected spectrum through three thermal cycles performed from room temperature up to 500, 750, and 800 °C, respectively. After reaching a temperature of at least 700 °C, the spectrum, which has been drastically altered by splicing, becomes stable and restores its single peak shape. A further stabilization cycle carried out at 800 °C for 80 min led to an estimation of the stabilizing time of the new single-peak reflected spectrum.
光纤光栅（FBG）传感器在许多科学和工业领域中用于评估机械部件的结构完整性，以及在非常高（高于600℃）或非常低（低温）的温度应用中。在极端温度应用中使用此类传感器的主要问题部分与反射光谱的不稳定性有关，反射光谱往往会融入本底噪声，部分与光纤机械性能的退化有关，这往往会加剧其固有的脆性。所有这些都增加了对坚固的镍保护涂层的需求，以确保光栅在高温环境下的完整性。此外，光纤光栅固有的脆性让人不禁要问，是否有可能修复一个断裂的、看似无法使用的传感器。通过这种方式，将一个单峰商用光纤光栅故意在光栅长度的中间折断并重新拼接，产生强烈不对称的类啁啾光谱；然后，在其表面电沉积镍涂层。这项工作取得的最重要成果是通过分别从室温到500℃、750℃和800℃进行的三个热循环，使高度扭曲的反射光谱得以再生。在达到至少700℃的温度后，因拼接而大幅改变的光谱变得稳定并恢复其单峰形状。在800℃下进行80分钟的进一步稳定循环，从而估算出新的单峰反射光谱的稳定时间。
