Electromechanical impedance modeling for adhesively bonded piezo-transducers

The electromechanical impedance (EMI) technique for structural health monitoring (SHM) and nondestructive evaluation (NDE) employs piezoelectric-ceramic (PZT) patches, which are surface bonded to the monitored structures using adhesives. The adhesive forms a finitely thick, permanent interfacial layer between the host structure and the patch. Hence, the force transmission between the structure and the patch occurs through the bond layer, via shear mechanism, invariably causing shear lag. However, the impedance models developed so far ignore the associated shear lag and idealize the force transfer to occur at the ends of the patch. This paper analyses the mechanism of force transfer through the bond layer and presents a step-by-step derivation to integrate the shear lag effect into impedance formulations, both one-dimensional and two-dimensional. Further, using the integrated model, the influence of various parameters (associated with the bond layer) on the electromechanical admittance response is studied by means of a parametric study. It is found that the bond layer can significantly modify the measured electromechanical admittance if not carefully controlled during the installation of the PZT patch.