FBG sensors monitor high-speed rail system

Ashley N. Paddock, ashley.paddock@photonics.com

Fiber Bragg grating (FBG) sensor systems installed along several lengths of China’s fast-expanding high-speed rail system help monitor the safety and structural health of the rails.

The FBG sensors, developed at Hong Kong Polytechnic University (PolyU), are small periodic structures created inside the 10-µm-core diameter of standard 125-µm-thick optical fibers. Measurement information is encoded in the wavelength of the reflected light from the FBGs. PolyU collaborated with Dalian Jiaotung and Southwest Jiaotong universities to study the FBG systems’ performance.

The team installed the monitoring system in several sections of the rail system, some of which previously were inaccessible. The hundreds of optical sensors provide information on vibration, temperature change, strain, acceleration and inclination, helping engineers monitor the condition of tracks and railcars as well as the foundation’s structural health. In addition, they keep track of train speeds, axle balance and vibration data for recording and further analysis. The sensors also were successfully installed onto the trains for wind-pressure measurement.

“High-speed trains, unlike conventional trains, experience wear and tear much faster; problems and damage growth also develop earlier,” said professor Tam Hwa-yau. “The need of real-time structural and condition monitoring systems for railways is imminent, as indicated by the increase in railway accidents and incidences around the world.”

Using ultrasonic wave technology, the team developed a system that can simultaneously detect cracks arising from metallic fatigue and corrosion of key parts in the track and rail. The system can be combined with laser actuating/sensing technology to monitor the structural health of tunnels, bridges, tracks, train bodies, bogie frames and wheel axles.

The recent success with using FBG sensors to monitor temperature, strain, vibration, acceleration and wind pressure of trains running at speeds beyond 300 km/h demonstrated the potential to develop the Smart Railway Sensor Network for high-speed railways based on FBG sensor technology, Hwa-yau said. “FBG-based monitoring systems … will herald a safer railway industry with reduced maintenance cost, optimized performance and capacity.”

Hwa-yau said that the university and its partners plan to conduct more research to develop FBG-based transducers that could extend the capabilities of current sensors to measure other crucial parameters important to the railway industry. They also are developing a system based on the information obtained from their sensors to provide diagnostic and prognostic information to railway operators.