13 Jun 2013
Continuous distributed and point fiber optics sensors increasingly deployed to replace conventional gauges.ElectroniCast, Aptos, CA, USA.
Monitoring and data transmission using fiber optic sensors and optical fiber in cabling is now commonplace in various applications, via intrinsic fiber optic sensors or extrinsic fiber optic sensors. With an intrinsic sensor, one or more of the sensing/measuring quantity or physical properties (measurand) of the optical fiber passes through or inside the optical fiber and therefore experiences a change. Extrinsic sensing takes place in a region outside of the optical fiber and the optical fiber acts as a transmission media of light to and from (linking) the sensing interface.
Fiber optic sensor technology has experienced impressive growth since ElectroniCast first started providing market and technology analysis of the subject since the early 1980s. In fact their analysts were tracking the various advanced photonic technologies, since 1976. In the reports, market forecast data refers to consumption for a particular calendar year; therefore the data figures are not cumulative.
Fiber sensors in stress analysis
Fiber optic sensing techniques make the task of measuring multiple sensing points over large intricate surfaces easier by combining many sensors on a single fiber. A fresh example of fiber optic sensors increasingly finding applications in stress measurement is exemplified by the launch of FBGS’s All Grating Fiber.
The company says that this development enables the positioning of sensors adjacent to one another, making it possible to monitor changes throughout a substantial entire structure [such as an aircraft’s wings and fuselage] to observe how mechanical influences at one point can affect another.
The DTG-LBL-1550-AGF is a low bend-loss fiber with densely spaced Draw Tower Gratings over the full length of the fiber. It is designed to be used with an OFDR (optical frequency domain reflectometry) system that allows rapid and precise measurements over a wide strain or temperature range with spatial resolution down to a few mm over the entire fiber length.
The chain can be configured such that more than 95% of the fiber contains gratings and the wavelength can be adjusted between 1510nm and 1590nm - and can vary within the array. The fiber is produced using a process that combines the drawing of the optical fiber with the writing of a Bragg grating. This process of simultaneously drawing the fiber and writing the grating results in spliceless, high strength FBG chains. The fiber coating is applied directly after the grating inscription so pristine fiber strength is maintained throughout the DTG manufacturing process.
The ability to build a high density of FBGs into a single fiber with high mechanical strength compared to conventional gratings, means sensing in harsh environments over large areas with a high resolution of measurement is now possible. With a breaking strength of >5% strain and a temperature operating range from -180°C to 200°C and although originally developed for use in the aerospace industry, the capabilities of the DTG fiber are also suited for structural testing within composites, automotive and the wind power industry.
About the Author
Matthew Peach is a contributing editor to optics.org.