Structural Health Monitoring of Composite Structures with Piezoelectric-Wafer Active Sensors

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications such as: (a) embedded guided-wave ultrasonics, i.e., pitch-catch, pulseecho, phased arrays; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; (c) passive detection (acoustic emission and impact detection). The focus of this paper will be on the challenges and opportunities posed by the composite structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper discusses damage modes in composites. Then, it reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Finally, the paper presents some experimental results with damage detection in composite specimens. The paper ends with conclusions and suggestions for further work