光ファイバセンサによる極低温でのひずみ計測技術とその航空宇宙分野における応用

Abstract

Strain and temperature measurement, especially in cryogenic environments, was studied using fiber Bragg grating (FBG) sensors for the purpose of the aerospace structural health monitoring. Although the relationship between the applied strain and the Bragg wavelength shift was the same as that at room temperature, the temperature-wavelength relationship became non-linear under cryogenic environment. In order to show the applicability of the sensor in aerospace applications, FBG strain and temperature sensors were embedded in a composite liquid hydrogen tank and measured in the cryogenic and pressurized environment. Encapsulated and small-size temperature sensors were used in this article and the temperature drift of the strain sensor was compensated by using the output of the temperature sensor. It was revealed throughout the experiment that the optical power loss could be critical in the case of existing large temperature difference. The practical solution for this issue was also discussed in this article.