Defect sensitivity of piezoelectric strip transducers based on planar Lamb waves

Long narrow piezoelectric fiber composite transducers that can generate planar ultrasonic guided waves are investigated for damage detection in plates. These strip transducers function well as actuators because the ultrasonic energy does not spread out and the signal remains strong. However, their suitability as sensors must be investigated because the received signal is integrated over the entire length of the transducer, potentially making them less sensitive to localized damage since the voltage is averaged over the length of the sensor. A segmented sensing scheme is introduced here and studied both numerically and experimentally. The strip transducer is subdivided into n segments, where n varies from 1 to 11, and the sensitivity to a through-thickness slot is assessed. The results indicate that there is a considerable improvement in defect sensitivity provided by segmented sensing. For a 130-mm-long strip transducer and a 15-mm-long slot, the transmission coefficient decreased from 0.86 to 0.70 to 0.59, while the reflection factor increased from 0.05 to 0.30 to 0.36 for the full 130-mm strip, a 31-mm-long segment, and a 7-mm-long segment, respectively.