United States Department of Transportation
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Implementation of advanced fiber optic and piezoelectric sensors : fabrication and laboratory testing of piezoelectric ceramic-polymer composite sensors for weigh-in-motion systems.
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1999-02-01
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[PDF-1.67 MB]
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Edition:Final report; Oct. 1996-Sept. 1998.
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Abstract:Weigh-in-motion (WIM) systems might soon replace the conventional techniques used to enforce
weight restrictions for large vehicles on highways. Currently WIM systems use a piezoelectric
polymer sensor that produces a voltage proportional to an applied pressure or load. Using this
phenomenon, these systems are already being tested for collecting traffic data, including weigh-inmotion,
measuring vehicle speeds, classifying vehicles by category and counting axles etc. The
polymer sensors are usually in the form of a long tape or cable embedded within a long block of
elastomeric material. These blocks are installed into grooves, which are cut into roads perpendicular
to the traffic flow. The biggest disadvantage of the present sensor technology is that the piezoelectric
output is not uniform with temperature and time, thus leading to large uncertainty in the data
collected. On the other hand, piezoelectric ceramic materials have a much more stable response
over a large temperature range. However, they are not used for traffic data sensors because of their
inherent brittleness. Piezoelectric ceramic/polymer composites are made with an active piezoelectric
ceramic embedded in a flexible non-active epoxy polymer. They hold a lot of promise for WIM
applications because of their flexibility and excellent piezoelectric properties similar to that observed
in bulk ceramics. In this research project, ceramic/polymer composite strips have been fabricated for
use as piezoelectric sensors for measuring large loads. After encapsulating the polymer and
composite sensors in elastomeric blocks in aluminum channels, the voltage outputs for different
loads, loading rates and temperature conditions have been determined. Also, the composite and
polymer sensor assemblies are being installed on a test road in order to perform actual
measurements.
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