Lamb Wave Tuning for Piezoelectric Wafer Active Sensor Applications in In-situ Structural Health Monitoring

An analytical and experimental investigation of the Lamb wave mode tuning with piezoelectric wafer active sensors (PWAS) is presented. The analytical investigation assumes shear lag transfer of tractions and strains. Analytical solution using the space-wise Fourier transform is reviewed and closed form solutions are presented for the case of ideal bonding (i.e., load transfer mechanism localized at the PWAS boundary). Experimental tests are run to verify the predicted tuning curves. The concept of “effective PWAS dimension” is introduced to account for the discrepancies between the ideal bonding hypothesis and the actual shear-lag load transfer mechanism. Two applications of PWAS transducers are presented to illustrate that the capability to excite only one desired Lamb wave mode is critical for practical structural health monitoring applications, including PWAS phased array technique (e.g., the embedded ultrasonics structural radar, EUSR) and the baseline-free time reversal process (TRP).