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Influence of External Excitation on Electromechanical Impedance Signatures



The using of electromechanical impedance (EMI) technique have been increasingly leading piezoelectric-ceramic (PZT) transducers to be applied to structural health monitoring (SHM) of real structures such as bridges, buildings, and airplanes. The PZT transducers are usually bonded on the structural surface and subjected to actuation so as to detect the damages in structures at the desired frequency range. The interrogation results in the electromechanical impedance signatures that will be changed by the presence of damage in structures which can be used to estimate the structural health or integrity according to the changes of the signatures. However, in fact most of the structures are in the vibration environment, and the effects of vibration on EMI signature may lead to erroneous diagnostic results of the structural integrity. So far there have yet been few investigations which take into account the effects on impedance signature. In order to obtain reasonable results, the effects of external vibration need to be considered when the electromechanical impedance technique is used to detect the damage of the structure. In this paper, three-dimensional finite element simulation of a simply supported plate with one PZT transducer bonded on surface is carried out to study the effect of external vibration on the PZT admittance signature. During the process of PZT scanning frequency, different frequencies of external vibration are imposed on the plate. Furthermore, experiments using a beam specimen mounted on a shaker which generate the external excitation are also conducted to demonstrate the effects. The results of the numerical simulation and the experiment demonstrate that different frequencies of the external excitation produce different degrees of effects on signatures.

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