Extracting Non-Propagating Modes in Waveguides via Electro-Mechanical Impedance Techn

Elastic waves in elongated bars exhibit complex dispersion, including propagating and non-propagating modes. We investigated the feasibility of extracting non-propagating modes through the electromechanical impedance (EMI) method in a rectangular bar structure through numerical simulation. First, the dispersion curves and mode shapes were computed to identify non-propagating modes. Second, a finite element model consisting of a piezoelectric lead zirconate titanate (PZT) patch and a rectangular bar was established to understand structural responses in the frequency-wavenumber (f-k) domain and the corresponding conductance spectra from the EMI measurements. Zero-group-velocity (ZGV) and cut-off frequency resonances were identified in both EMI signature and structural responses. The paper demonstrated the potential of the proposed EMI technique to extract non-propagating modes in waveguide structures for quantitative nondestructive evaluation (NDE).