Embedded Ultrasonics NDE with Piezoelectric Wafer Active Sensors

ABSTRACT: The use of piezoelectric wafer active sensors (PWAS) for embedded ultrasonic nondestructive evaluation (NDE) is described. PWAS structure and principle of operation are presented. The interaction between PWAS and ultrasonic Lamb waves is modeled and analyzed, and excitation “sweet spots ” for preferentially exciting certain Lamb wave modes are identified. Recent trends in guided-wave ultrasonic NDE and damage identification are briefly reviewed. Then, the use of PWAS for embedded pulse-echo detection of structural cracks is exemplified. For large area interrogation, PWAS phased arrays are used in conjunction with the embedded ultrasonics structural radar (EUSR) algorithm to create scanning Lamb wave beams. For local area interrogation, the use of PWAS in conjunction with the electromechanical (E/M) impedance method is discussed with examples of local area crack detection in circular plates and aircraft panels. Spectral classification methods based on overall statistics and neural networks are discussed. Passive PWAS usage for acoustic emission and impact detection is presented. The use of PWAS for Rayleigh wave ultrasonics is also illustrated. Finally, we evaluate the role and opportunities of PWAS as the enabling technology for large area structural health monitoring, damage detection, and embedded NDE