Design, implementation, and comparison of guided wave phased arrays using embedded piezoelectric wafer active sensors for structural health monitoring

Phased array can interrogate large structural areas from a single location using ultrasonic guided waves generated by tuned piezoelectric wafer active sensors that are permanently attached (embedded) to the structure. Various array parameters determine the array beamforming and steering characteristics. This paper aims to bring up several one or two dimension array designs and research on their beamforming properties and damage detection performance through both analytical simulation and laboratory experiments. The paper will firstly present the generic guided wave phased array beamforming formulation and explain how the beamforming characteristics are affected by the array parameters such as number of elements, element spacing, and steering angle. Preliminary work of implementing a one dimensional linear phase array is then followed to exemplify how our embedded ultrasonic structural radar (EUSR) scans and detects damage on the plate structures. However, such a linear array has the limitations that it has limited scanning range due to the beamforming directionality deficiency and it can only scan the 0o~180o range either in front of or behind it, i.e., it can not tell if the damage is in the positive or negative direction in the polar coordinates. Hence, we proposed several improved array designs including: (1) a miniaturized array using smaller PWAS; (2) an array using rectangular PWAS; (3) a cross-shaped two dimensional array; (4) a L-shaped two dimensional array. Extensive simulation work has been done to explore the beamforming and beamsteering properties of those arrays. Laboratory experiments have also been conducted to testify the arrays damage detection abilities. The results show that the miniaturized array can look into larger area and be used for damage detection of compact specimen with complicated geometry. Signal rectangular PWAS has directional rather than omnidirectional beamforming which resulting in improved beamforming of the phased array using such PWAS. Two dimensional arrays show directional beamforming within full range of 0o ~ 360o degrees though having limited working steering angles. We finally end up with discussion and conclusion of the arrays and some expectations for future work.