The local anti-resonance of guided elastic waves: An analytical perspective and application for wave mode tuning

Despite the proven high sensitivity of nonlinear features in guided elastic waves to material degradation and undersized defects, the accurate measurement of defect-induced nonlinear wave features remains challenging primarily due to the pronounced nonlinear waves from disturbing sources. In this investigation, an analytical investigation of the previously un-explored local anti-resonance (LAR) phenomenon induced by guided elastic waves is performed, and the capability of LAR for tuning guided wave mode is identified which enables the suppression of undesired nonlinear waves from the disturbing sources. In the analytical investigation, the normal mode expansion method is adopted to analyze the guided wave reflection at the boundaries of a flat bottom hole, on which basis the generation of local anti-resonance is interpreted from the perspective of destructive interference of trapped waves in the hole. The capability of LAR for guided wave mode tuning is demonstrated, and thus an approach leveraging this capability is developed to suppress the undesired higher harmonics in guided waves, allowing for the precise acquisition of nonlinear waves associated with material defect. Numerical simulations and experimental investigations are performed for the proof-of-concept. This investigation presents a significantly simpler and more implementable design for achieving mode tuning compared to existing solutions. Addressing the critical obstacle for accurate measurement of nonlinear features in guided waves, the proposed method can remarkably enhance the application of structural health monitoring and nondestructive evaluation methods based on nonlinear features in guided waves.