Non-axisymmetric Lamb wave excitation by piezoelectric wafer active sensors

A Lamb wave-based structural health monitoring system requires the exact knowledge of the dynamical behavior of piezoelectric actuators. Since piezoelectric wafer active sensors (PWASs) with a disk-wrapped electrode are used in many practical applications, a detailed description of the radiation field is essential to enhance the damage detection sensitivity. It has been shown in the literature that the radiation pattern is often directional and frequency-dependent. While a uniform radiation occurs at low excitation frequencies of several tens of kilohertz, the radiation pattern becomes strongly non-axisymmetric when the excitation frequency increases. The theoretical considerations and experimental studies in this paper show that this effect can be attributed to the influence of the complex actuator shape with disk-wrapped electrode. Therefore, simulation procedures based on an integral approach and a pin-force model are compared with experimental measurements with a laser-Doppler vibrometer (LDV).