Fiber optic distributed strain, acoustic emission, and moisture detection sensors for health maintenance [aircraft testing applications]

Optical fiber sensors are rapidly emerging as viable alternative's to electrical sensors as effective means of health monitoring in harsh environments. These sensors are tolerant to extreme temperature, EMI, shock and vibration, and offer reduced weight and increased accuracy over conventional instrumentation. As a result, these sensors have begun to replace conventional sensors in harsh environment applications. This paper discusses the development and demonstration of three optical fiber sensor technologies - distributed Bragg grating strain, interferometer-based acoustic emission, and long period grating moisture detection. The Bragg strain technology allows multiplexing of thousands of single-point strain sensors along a single optical fiber. Optical fiber acoustic emission sensors can be used to determine crack growth in metal components or delaminations in composite structures. Long period grating moisture sensors are used to prevent corrosion by detecting moisture and humidity under lap joints. Continued development of these sensor technologies for non-destructive evaluation and results are presented in this paper.