A new optic fiber sensor that enables identification of water presence and its phase change from liquid to solid (namely, from water to ice) at its tip is introduced. When light travelling through material 1 and reaches its boundary, a part of it is refracted and gets into Material 2 beyond the boundary and the other part gets reflected, turns its direction around and keeps travelling through material 1. The ratio between the refracted and reflected light is known to depend on the difference between refractive indices of materials 1 and 2. This fundamental law can then be used to make a sensor that can detect presence of water around it and its phase change. A series of experiments were conducted and the results show that the proposed optic fiber sensor can identify state of phase change of water very clearly, which is of great engineering significance in light of controlling and managing ground freezing processes or monitoring freezing process of water in rock joints.
Akutagawa et al. (2017) have developed a unique optic fiber sensor that enables identification of water presence at the tip of an optic fiber sensor, in a way that is very different from other methods of optic fiber sensing (for example, Hill et al 1978, Meltz et al 1989, Funnel et al 2015). The fundamental mechanism behind this monitoring technique lies in nature of how light travels between two materials with different refractive indices. Refractive index of light is a unique property for each engineering material, and it is also known that it changes with temperature or with material phase. It suggests that if the proposed fiber sensor is placed in water, for example, and water temperature drops beyond freezing point, that phase change from liquid to solid could be identified. This paper reports the results of a series of laboratory experiments in which optic fiber sensor was used to monitor phase change of water from liquid to solid phases. The results show that the proposed optic fiber sensor can be used to identify state of phase change of water, which is of great engineering significance for monitoring ground freezing processes in civil construction or monitoring freezing process of water in rock joints.
The fundamental schemes used to obtain optic data by plastic optic fiber (POF) were described in Akutagawa et al. (2014, 2015) in which TWIN FIBER sensor and GAP sensor were introduced. In this paper, a new sensor called RR sensor is proposed and described hereafter.
