Fiber optic sensors for predictive health monitoring

The ability to predict the onset of failure in mechanical systems is key to the reduction in maintenance costs, downtime, and health hazards in industrial environments. Vibration monitoring can be used to spot mechanical problems, trigger preventative maintenance and diagnose the health of rotating machinery. Accelerometers are used in this role to detect defects in rotating components through analysis of harmonics in the power-frequency distribution. Further, high frequency acoustic emission sensors can be used to determine crack growth in metal components or failures in composite structures. Currently, a variety of MEMS accelerometers and piezoelectric acoustic emission sensors are used in health monitoring that are limited by their size, cost, and performance. Optical fiber sensors are rapidly emerging as viable alternatives to these devices 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. Optical fiber sensors offer much smaller size, reduced weight, ability to operate at temperatures up to 2000 degreesC, immunity to electromagnetic interference, resistance to corrosive environments, inherent safety within flammable environments, and the ability to multiplex multiple sensors on a single optical fiber. This paper presents the research and development of both low-profile fiber optic-based acoustic emissions sensors for use in nondestructive evaluation systems and fiber optic accelerometers for harsh environment health monitoring applications.