Lamb wave excitation and detection with piezoelectric elements: Essential aspects for a reliable numerical simulation

Lamb waves are guided elastic waves in thin walled structures. Studies show that Lamb waves in form of wave packets are useful for application of structural health monitoring (SHM) of thin walled structures as e.g. aircraft panels. By using piezoelectric elements it is possible to generate as well as to receive Lamb waves in a simple manner. If there is a damage in a thin walled structure, e.g. a plate, the traveling Lamb waves are reflected at this damage and a change in mode shape may happen. With a well designed actuator-sensor system the detection and even the localization of the damage is possible. However, experiments reveal that the analytically calculated response functions for in-plain strain curves of a thin aluminum plate, which is excited with a square-shaped piezoelectric transducer, does not agree satisfactory with measurement results. Particularly the amplitude of the experiment signal is much lower than predicted by analysis. This can lead to the problem that in an unfavourable configuration of the whole measurement setup (size of the transducers, excitation signal, test equipment, etc.) the signal is too weak to be measured. Here the questions arise about the reason for this effect and how the amplitude of the sensor signal can be improved. Another challenge is the numerical analysis of the Lamb wave propagation, especially the Lamb wave generation and detection in Finite Element models. There are several effects, like material damping, coupling between the piezoelectric element and the structure or the measurement principle of piezoelectric transducers, which influence the Lamb wave behaviour in the simulation. These effects must be considered in numerical models to receive realistic simulation results. This article gives an overview on such effects, on their origin and how adverse influences can be reduced.