A new optical system can detect problems
in structures such as natural-gas pipes and concrete
columns more precisely and potentially earlier than before.
University of Ottawa physicists presented the invention this week
Optical Fiber Communication/National Fiber Optical Engineer Conference
(OFC/NFOEC) in Anaheim, Calif.
Already being considered for commercial production, the new system
can catch much earlier signs of costly and dangerous structural
failures than previously possible.
Called the Distributed Brillouin
Sensor (DBS), the system uses fiber optics to detect deformation,
cracks, and bending in two structures under real-world conditions.
In one demonstration, conducted with Edmonton-based engineering firm
C-FER Technologies and TransCanada PipeLines Ltd., the Ottawa
researchers (Xiaoyi Bao, email@example.com) deployed the DBS system on
a section of steel pipe designed to transport natural gas. Laying
10 lines of optical fiber along the axis of the pipe, they created
one pulse of laser light and one continuous light wave, each
traveling in opposite directions in the fiber.
When the researchers
applied tension and compression to the pipe to mimic real-world
disturbances, it produced vibrations (sound waves). Through a
phenomenon called the Brillouin effect, these sound waves then
slightly changed the speed of light in the affected part of the
fiber and consequently altered the frequency difference between the
two propagating light waves, providing precise information on the
mechanical strains that were applied to the pipe.
structural health analysis, which is done on a spot-by-spot basis,
DBS can detect problems over all points in the entire structure and
pinpoint the location of a structural deformation to within 5
centimeters, while measuring mechanical strains as low as 20
microstrains (20 millionths of a strain, a dimensionless property
that generally reflects the structure's change in length over its
original length). This exceeds the 1-meter resolution and 50
microstrains that the construction industry has wanted and expected.
In another demonstration, conducted with civil engineers at the
University of Ottawa, the researchers tested the DBS system on a
concrete column encased with fiber-reinforced rods and sheets.
Subjecting the column to simulated seismic forces such as those that
would occur in an earthquake or tsunami, the researchers could
detect signs of debonding (in which the concrete detached from the
fiber casing) and the cracks (crushing) of concrete as a result of
Unlike competing techniques, the system could
readily tell the difference between debonding and crushing. The
Ottawa researchers say that DBS can prevent potentially
life-threatening and environmentally damaging accidents and
multimillion-dollar repairs. In addition, the technique can improve
the testing of structures and materials by providing valuable
information during the testing process.
Paper OTuL7 at OFC/NFOEC meeting