This paper presents the embedding of calibrated fiber optic cables into a simplified concrete structure to obtain spatially dense internal strain measurements under a 3-point bending load. Taking advantage of the millimeter-level spatial resolution of the measurement system, it is possible to identify the onset of cracking within the concrete and compare the behavior of both unreinforced and steel rebar-reinforced structures. Integrating these sensors during new construction, or retrofitting into existing structures, will enable the rapid and cost-efficient inspection and lifetime monitoring, identifying impending failure before a catastrophic event occurs. This is exemplified by two applications in France: instrumenting a tower’s foundation and measuring settlement of a pillar built using a new design.
Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic
sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. We examine
aerospace applications that benefit from HD-FOS, such as for defect detection, FEA model verification, and structural
health monitoring. We describe how HD-FOS is used in applications spanning the full design chain, review progress
with sensor response calibration and certification, and examine the challenges of data management through the use of
event triggering, synchronizing data acquisition with control signals, and integrating the data output with established
industry protocols and acquisition systems.
Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. OFDR employs swept laser interferometry to produce strain or temperature vs. sensor length with fiber Bragg gratings (FBGs) or Rayleigh scatter as the source signal. We look at the influence of HD-FOS on design and test of new, lighter weight, stronger and more fuel efficient vehicles. Examples include defect detection, model verification and structural health monitoring of composites, and temperature distribution monitoring of battery packs and inverters in hybrid and electric powertrains.
Luna recently demonstrated a novel optical phase-based algorithm for removing the adverse effects of fiber motion at frequencies far above the scan rate on high-resolution measurements of Rayleigh scatter using Optical Frequency Domain Reflectometry (OFDR) for static strain and temperature measurements. By comparing dynamic OFDR Rayleigh scatter measurements to a static reference, it is possible to extract the time-varying phase signal in real time. The same algorithm, applied to successive segments along an unbonded single mode fiber, is an effective means of monitoring the spatial distribution of high frequency optical phase perturbations caused by vibration and acoustic wave propagation in the fiber. We will discuss tradeoffs between scan speed, scan duration, range, spatial resolution, vibration sensitivity and vibration frequency range, provide measurement examples, predict limiting specifications for practical system performance based on current commercial OFDR products, and compare these limits to those of distributed acoustic sensing techniques based on Optical Time Doman Reflectometry.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.