Lamb wave is a special type of elastic wave that is widely employed in structural health monitoring systems for damage detection. Recently, piezoelectric (piezo) patches are becoming popular for Lamb wave excitation and sensing because it can be utilized as an actuator and a sensor. All published work assumed that the Lamb wave displacement field generated by a piezo patch actuator is axi-symmetric. However, we experimentally observed that the displacement fields excited by the piezo patch actuator are directional and this directionality is frequency dependent. In this paper, we present a simulation model that explains this phenomenon by incorporating the bending deformation of the piezo actuator into the calculations of the Lamb wave generation. The driving forces acting on the host plate are calculated from the out-of-plane deformation of the piezo patch through the deformation of the bonding layer. Treating these forces as tone-burst point loads, the displacement field excited by the piezo patch is constructed from the displacement solutions of time-harmonic point loads. Simulation results confirmed that a piezo patch vibrating at certain vibration mode can result in the directional and frequency dependant displacement fields observed by the experiment.

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