Tunable Lamb Wave Bandgap Based on 90° Diffuse Domain Walls in Ferroelectric Thin Films

Ferroelectric and piezoelectric thin films hold significant potential for tunable acoustic devices. While the elastodynamic properties of ferroelectric thin films have been studied for various domain structures, the influence of diffuse domain walls on acoustic waves remains unexplored. In this study, using a phase-field perturbation model, the effect of 90° diffuse domain walls on Lamb wave propagation in ferroelectric thin films is investigated. Modal analysis reveals that the local negative shear modulus induces localized shear vibrations within the diffuse domain walls, disrupting the symmetry of Lamb wave mode in ferroelectric thin films. This disruption further leads to strong coupling between distorted symmetric and antisymmetric Lamb modes, resulting in multiple bandgap formations. The bandgaps can be successfully tuned through changing the spacing of domain walls, which can be easily realized by applying external strains or electric fields. In addition, the nonlinear scaling laws are predicted for the bandgaps, which are in good agreement with previous experimental reports. This work suggests an effective method for designing tunable acoustic metamaterials based on ferroelectric thin films.