In situ PZT diagnostics using linear reciprocity under environmental and structural variations

Guided waves generated by a spatially distributed array of piezoelectric are being evaluated by many researchers for structural health monitoring applications. These surface-mounted transducers, which are typically Lead Zirconate Titanate (PZT), 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 conditions. Existing transducer diagnosis techniques often identify PZT defects by comparing current data to baseline data previously measured from the pristine condition of the bonded transducers. This baseline-dependent approach can result in false alarms because of its susceptibility to operational, structural and environmental variations. In this study, a methodology for PZT transducer diagnosis is developed to identify damaged or poorly bonded transducers by quantifying the degree of linear reciprocity for waves propagating between pairs of surface-mounted transducers on metallic structures. The proposed method does not require direct comparisons of signals to baselines, and also is independent of wave mode(s), excitation signal, structural complexity and edge reflections. The efficacy of the proposed diagnostic technique is evaluated via experiments with PZT transducers instrumented on an aluminum plate under varying environmental and structural conditions and also on a complex structure.