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Piezoelectric ceramic-polymer composites for weigh-in-motion sensors

Piezoelectric materials produce a voltage proportional to an applied pressure. Using this phenomenon, piezoelectric polymer sensors are already being used for collecting traffic data including weight-in-motion, measuring speeds and counting axles. The polymer sensors are usually in the form of a long tape or cable embedded within long blocks of elastomeric material. These sensor assemblies are then installed into grooves, which are cut into roads perpendicular to the traffic flow. The biggest disadvantage of these sensors is that the piezoelectric output is not uniform with temperature, thus leading to large uncertainty in the data collected. Piezoelectric ceramics have a much more stable response over a large temperature range. However, until now they have not been used for traffic data sensors because of their inherent brittleness. In this research project flexible ceramic/polymer composite strips have been fabricated for use as piezoelectric sensors for measuring large vehicle loads. Here, the ceramic is the active piezoelectric material that is embedded in a flexible non-piezoelectric polymer. After encapsulating these sensors in elastomeric blocks in aluminum channels, the voltage output of the composite for different loads have been determined. Also, these composite sensor assemblies are being installed on a test road in order to perform actual measurements.