The objective of this research program is to study and develop an improved guided wave phase tuning technique and its practical applications to nondestructive evaluation (NOE) for inspecting thin and slender members in civil, mechanical and aerospace structures. An extended study of a novel method referred to as "synthetic phase tuning" (SPT) is being developed through this project, which could resolve many critical problems associated with guided waves by eliminating the complexities due to their multimodal and dispersive nature. The innovative concept of the SPT is to reinforce a specific wave mode of interest while suppressing or squelching undesired wave modes by constructing a phase-tuned wave in a virtual domain. This operational scheme may allow for extremely flexible guided wave pulse-echo operations with excellent spatial and temporal resolutions. The program is to understand the phase-tuning mechanisms and to study the wave-material (structure) interactions using various analytical and numerical methods. Various influencing factors such as the characteristics of spatio-temporalloading and transducer parameters, e.g., element width, number of elements, inter-element spacing, operating frequency, are investigated both theoretically and experimentally. In addition, the SPT scheme is extended using the laser- ultrasound techniques in order to relax the current limitations of narrow signal bandwidth. The concept of SPT may have a substantial and direct impact not only on scientific and technological advancements in the field of NOE, condition assessment, and health monitoring, but also on the industrial sectors in NOE manufacturing and services. Although the focus is specifically on NOE, the method does not preclude extensions to a broad spectrum of disciplinary fields such as communication, geophysical explorations, structural control, and MEMS.
