The embedded ultrasonic structural radar (EUSR) was developed based on phased array technology. It can interrogate large structural areas from a single location using ultrasonic guided Lamb and Rayleigh waves generated by tuned piezoelectric wafer active sensors (PWAS) that are permanently attached to the structure. This paper brings together several aspects of the implementation and application of EUSR to structural damage detection: (a) improving the near field damage detection; (b) designing optimized phased-array patterns; (c) designing a mini phased array for compact structures with complicated geometries and multiple boundaries. Firstly, we deduced a generic formulation for phased array directional beamforming using the exact traveling waves formulation without the limiting parallel-rays assumption used by other investigators. This algorithm has been implemented in the EUSR LabVIEW program and its performance has been verified through simulation and experimental tests. Secondly, we studied the beamforming and lobe steering characteristics of a 1-D linear array design. The influence of several geometry parameters was discussed in order to achieve the optimal directionality, including the number of sensors in the phased array, the spacing between adjacent sensors, and the steering direction angles. Extensive simulation studies have shown that the well-behaved directional beamforming can be achieved with judicious array design. Proof-of-concept experiments for testing these results have also been set up and the preliminary results are confirming the effectiveness of our approach. Thirdly, we investigated the possibility of applying the EUSR phased array method to compact specimens and proposed the design of a mini phased array. Laboratory experiments have been carried out to prove the successful implementation of this concept. Finally, the paper ends up with discussions and conclusions regarding the beamforming, optimization and implementation of the PWAS phased arrays, as well as suggestions for further work.

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