Generation of selective single-mode guided waves by d₃₆ type piezoelectric wafer

In general, mixed modes and dispersion of guided wave occur at any excitation frequency, while single modes are needed for effective nondestructive evaluation of structures. In this work, we present an approach to generate a selective single-mode guided wave in plate-like structures by exploiting the unique directionality of the d₃₆ type piezoelectric wafer and the symmetry of fundamental guided wave modes. Specifically, we devise a unified fundamental shear horizontal (SH₀) wave/fundamental antisymmetric mode (A₀) wave directional transducer pair by attaching the d₃₆ type piezoelectric wafers back to back on the opposite sides of the plate to provide selective, directional single-mode guided waves for actuation and sensing. Originally, the d₃₆-type piezoelectric wafer, poled and cut from the lead magnesium niobate-lead titanate crystal, produces a mixture of the in-plane SH₀ (symmetric) mode and out-of-plane A₀ (asymmetric) and S₀ (symmetric) modes. By applying the in-phase or out-of-phase applied electrical field to the coupled d₃₆-type piezoelectric wafer pair, our devised approach generates selective single modes, SH₀ or A₀, respectively, to propagate in the structure. We describe the theoretical development of our approach and conduct both numerical simulations and laboratory experiments for validations.