A fully coupled model for actuation of higher order modes of Lamb waves

Abstract

Lamb waves have proven to be a valuable tool for structural health monitoring (SHM) of plate-like structures susceptible to degradation and failure. It is well-known that their multi-modal propagation characteristic could be both a challenge and an opportunity. Piezoelectric transducers are widely used in SHM applications because of their low cost, small profile and high electromechanical coupling. Properly designing a piezoelectric transducer to excite a particular mode is of great importance to successful SHM practice. Mode tuning capability of piezoelectric transducers has been studied both theoretically and experimentally in the literature for exciting A0 and S0 modes. However, the higher order Lamb waves are not fully studied for their tuning capability. Also, the transducer is usually modeled separately from the waveguide and their coupling is through the in-plane surface traction. This assumption may induce inaccuracy if the dynamics of the actuator are not negligible. Additionally, the driving circuit is not usually included in the current actuator-waveguide models such that the power of excited wave could not be evaluated. In this work, a fully coupled finite element model created for general Lamb wave excitation using piezoelectric transducers is developed. The model comprises three components, electrical driving circuit, piezoelectric element and linear elastic waveguide. The preferential excitation of higher order Lamb wave modes using a single piezoelectric element has been studied and demonstrated experimentally on aluminum plates.