ABSTRACT Title of dissertation: PIEZOELECTRIC PHASED ARRAY ACOUSTO-ULTRASONIC INTERROGATION OF DAMAGE IN THIN PLATES

systems can provide substantial benefits for aging aerospace systems as well as newer systems still in the design process. In aging aerospace systems, a retrofitted SHM system would alert users of incipient damage preventing catastrophic failure. For newer systems, incorporating a SHM approach and using CBM techniques can re-duce life-cycle costs. Central to such SHM and CBM systems is the ability to detect damage in a structure. Traditional approaches to damage detection in structures involve one of two methods. In the modal dynamics approach, the natural frequencies and modeshapes of a structure shift when damage occurs. The location, type, and amount of dam-age is determined by the shifts in the modal properties due to damage. Alternately, in an Ultrasonics approach, the structure is scanned with a specialized transducer which induces high frequency vibrations in the structure. Damage in the struc-ture is inferred when these vibrations are altered. In the same vein as Ultrasonics, Acoustic Emission based methods listen for energy release in the structure upon defect growth. All of these techniques have limitations which hinder their usage i