Piezoelectric Transducer Diagnostics via Linear Reciprocity for Guided Wave Structural Health Monitoring

Guided waves using spatially distributed piezoelectric transducers are being applied to many structural health monitoring applications. These surface-mounted transducers, which are typically lead zirconate titanate, are generally assumed to be both undamaged and properly bonded to the host structure during usage. However, this assumption may not be valid, particularly after long-term operation under realistic environmental conditions. The transducer integrity becomes even more critical for aerospace applications because of the inevitably harsh operational conditions. In this study, a methodology for piezoelectric transducer diagnosis is developed to identify both damaged and poorly bonded transducers by quantifying the degree of signal reciprocity for guided waves propagating between pairs of surface-mounted transducers. The proposed method does not require direct comparison of signals to baselines, and it is independent of structural complexities such as geometrical features and boundaries. The method is also insensitive to environmental and operational conditions, such as temperature and applied loads, and is therefore not susceptible to false alarms caused by such variations. The efficacy of the proposed diagnostic technique is evaluated via two-dimensional simulations followed by experiments under varying environmental and operational conditions for piezoelectric transducers mounted on an aluminum plate.