Generation and Detection of Zero-Group-Velocity Lamb Waves With Direct-Write Piezoelectric Transducers for Nondestructive Evaluation

Zero-group-velocity (ZGV) Lamb waves are usually excited and detected using noncontact laser ultrasonic systems, as contact techniques such as using conventional bulky discrete piezoelectric transducer may cause interferences and errors in identifying the ZGV Lamb waves due to the large mass and stiffness introduced. Nevertheless, contact transducers have many advantages over the laser ultrasonic method, including cost, sensitivity, safety, and efficiency. Here, a contact technique is explored by using a lightweight and low-profile direct-write piezoelectric ultrasonic transducer (DWT) made of piezoelectric polymer coating to generate and detect the ZGV Lamb waves. The frequency shift and wave attenuation of the ZGV Lamb waves and their ability for monitoring adhesive bonded structure are investigated with both numerical modeling and experimental testing, with a comparison between the DWT and discrete piezoelectric transducer. The potential of the DWT for generating and detecting ZGV Lamb waves for ultrasonic nondestructive evaluation (NDE) is demonstrated by overcoming the drawbacks of discrete piezoelectric transducers.