Researchers at the University of Illinois at Urbana-Champaign (UI; Champaign, IL) are fabricating fiber-optic sensors that could someday improve train safety by detecting flaws in rails and wheels. According to Shun-Lien Chuang, a UI professor of electrical and computer engineering, the optical fibers, which would be attached to rails and wheels, would provide feedback related to environmental changes, such as the weight of a passing train or the strain created by a cracked, broken, or buckled rail.
In projects sponsored by the Association of American Railroads (AAR) and the Transportation Research Board at the National Academy of Science, Chuang and research assistants are developing different sensor designs for specific applications. In one example, which provides feedback using optical time-domain reflectometry, the weight of a passing train causes strain in the rail that is detected by the fiber. In addition to detecting damaged rails, this sensor could also provide feedback on a train's position and speed.
Another design is based on a micro-bending effect. "Fiber optics operate on total internal reflection," says Chuang. "When the fiber bends, some of the light leaks out, and we can calibrate the intensity of the optical transmission as a function of the applied bending pressure." By introducing a certain amount of micro bending into the fiber, the researchers can also measure pressure related to the weight of passing railcars or deformities such as flat spots in rail-car wheels. The sensors are currently being tested at the AAR's transportation Technology Center in Pueblo, CO.