The use of distributed sensors for monitoring the structural health of large structures such as dams or bridges has for long generated particular interests. With over 1 million sensing points, a newly developed fiber optic distributed sensor could offer significant faster detection of structural problems than is currently available. A team of researchers from the University of Alcala (UAH) in Spain along with Swiss Federal Institute of Technology (EPFL) have come up with a like wise fiber-based sensor with which it is possible to precisely detect erosion or cracking in large structure due to any natural or man-made disaster.
Fiber optic distributed sensors are known to be ideal for monitoring infrastructure because they can be used in harsh environments and in areas that lack a nearby power supply. If a single fiber is placed along the length of a bridge, for example, changes in the structure at any of the sensing points along the optical fiber will cause detectable changes in the light traveling down the fiber. Although the popularity of fiber optic distributed sensors is growing, they are currently used primarily to detect leaks in oil pipes and to monitor for landslides along railroads.
According to the research report published in The Optical Society (OSA) journal Optics Letters, the researchers stated that the fiber optic distributed sensor can sense strain and temperature changes from 1 million sensing points over a 10-kilometer optical fiber in less than 20 minutes. The new sensor is about 4.5 times faster than previously reported sensors with 1 million sensing points. Although there isn’t a magic number, more sensing points means fewer fiber-optic units are needed to monitor an entire structure. This simplifies the overall sensing scheme and could potentially reduce costs.
The new sensor uses an approach known as Brillouin optical time domain analysis, which requires pulsed and continuous wave laser signals to interact. The researchers discovered that the traditional method of generating the continuous signal caused distortions in the system at higher laser powers. These problems could be avoided by changing the way that laser signal was generated, allowing them to increase the laser power and hence improve the sensing performance. According to the team, the detrimental effects studied and corrected have been affecting the performance of commercially-available Brillouin optical time domain sensors for some time but if manufacturers incorporate their optimization into their sensors, it could improve performance, particularly in terms of acquisition speed.
Using the new approach, the researchers demonstrated that they could measure the temperature of a hot spot to within 3 degrees Celsius from the end of a 10-kilometer long fiber.
The researchers are now working to make the sensor even faster by looking for ways to further reduce the acquisition time. They also want to increase the density of sensing points to more than one per centimeter, which could allow the technology to expand into completely new areas such as biomedical applications. The optical fibers could also potentially be adapted for use in textiles, where the sensors could help to monitor a person’s health or screen for disease. For example, the researchers think it might be possible to use the fiber optic sensors to detect temperature deviations that are present in breast cancer. For this type of application, more sensing points in a smaller area would be more important than using a particularly long fiber.