Linear phased arrays with selectable shear and lamb wave modes for damage detection in metallic structures

Piezoelectric phased arrays (PA) are an attractive approach for damage detection in metallic plate structures due to their ability to steer and focus guided waves to accurately detect structural damage. In this paper, a PA is designed using lead magnesium niobate-lead titanate (PMN-PT) piezoelectric transducer elements. PMN-PT is a d 36 piezoelectric that can generate symmetric (S), anti-symmetric (A), and planar shear (SH) Lamb waves in thin-walled structures. Unlike conventional phased arrays based on d 31 piezoelectric transducers (e.g., lead zirconate titanate) that generate multiple mixed wave modes, a PMN-PT phased array with array elements collocated on both sides of the plate can selectively generate individual wave modes in the structure. Selected single mode simplifies the interpretation of received waveforms, which is promising for faster damage identification. After designing the PMN-PT phased array based on element collocation, experimental validation is performed with a 14-element phased array attached to a thin aluminum plate. Laboratory experiments are executed using a high-speed data acquisition system that can command the phased array elements in parallel while triggering a laser Doppler vibrometer that synchronously measures out-of-plane wave fields in the plate. The experiments validate the ability of the phased array to selectively generate, steer, and focus A 0 , S 0 , and SH 0 wave modes to localize and characterize damage introduced in the plate. Numerical simulations by the local interaction simulation approach are adopted to complement the laboratory experiments and to explore cracks in the aluminum plate to illustrate the detection capability of the proposed approach.