Embedded Ultrasonic Structural Radar With Piezoelectric Wafer Active Sensors for the NDE of Thin-Wall Structures

Embedded-ultrasonics structural radar (EUSR) is a new concept and methodology for in-situ nondestructive evaluation (NDE) and structural health monitoring (SHM) of thin-wall structures. EUSR consists (a) an array of piezoelectric wafer active sensors (PWAS) embedded into the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. EUSR utilizes guided elastic waves (Lamb waves) generated omnidirectionally into the thin-wall structure by surface-mounted permanently-attached PWAS. The paper starts with the general concepts of the EUSR algorithm: transmission beamforming, reception beamforming, and time of fight determination. Next, details of the Lamb wave generation with PWAS, verification of group-velocity dispersion curves, identification of optimal excitation frequency, and confirmation of wave front omnidirectionality are discussed. In the third part of the paper, the actual implementation of the EUSR method in a proof-of-concept demonstration is presented. The construction of the PWAS phased array is described, and detection of cracks located broadside and offside of the PWAS array is illustrated. The method is shown to be easy to use through a visually interactive LabView™ interface. Very good detection accuracy is observed. Though the proof-of-concept experiments presented in this paper were illustrated on metallic structures, the EUSR concept works just as well on composite and hybrid structures.