Abstract
As the applications of fiber Bragg gratings (FBGs) continue to grow and become more advanced, it becomes necessary to understand their behavior when exposed to high temperatures in unique situations. In these experiments, uniform 1530-nm fiber Bragg gratings and Type K Cr-Al thermocouples were embedded in three-ply carbon fiber composites. A 100 W high energy laser (HEL) heated the composites to high temperatures over timespans less than one second, and FBG spectral data and thermocouple temperature data were collected during each HEL heating test. The data from three high energy laser tests that represent different levels of damage to the FBG are analyzed to explore the spectral response and thermal decay of embedded FBG sensors when exposed to high temperatures over short timespans. Results are compared to a previously proposed power-law model describing the decay of FBGs in bare fiber when held at constant temperatures over much longer timespans.
Highlights
Fiber Bragg grating (FBG) sensors have become an area of significant research interest due to their relatively small size, high sensitivity and quick response times as well as their immunity to electromagnetic interference [1]
This paper focuses on the temperature limits and thermal decay of embedded FBG sensors in such an application
The thermocouple was connected to an Omega RDXL12SD data logger and the fiber Bragg grating sensor was connected to a SmartScan Dynamic FBG Interrogator
Summary
Fiber Bragg grating (FBG) sensors have become an area of significant research interest due to their relatively small size, high sensitivity and quick response times as well as their immunity to electromagnetic interference [1]. FBG sensors are responsive to changes in temperature, which makes them useful in applications such as process monitoring during pharmaceutical production [11] and health monitoring of steel structures [12], fires [13], oil pipelines [14], and laser strike detection [15,16]. This paper focuses on the temperature limits and thermal decay of embedded FBG sensors in such an application. The experiments outlined in this paper were conducted to analyze the behavior of embedded FBG sensors in high energy laser (HEL) sensing applications, where large, sudden, and non-uniform temperature transients are possible. There are several examples of high-temperature FBG experiments in recent literature, including studies of FBG decay at constant temperatures during annealing [17,18], FBG spectral shift
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