Generating defect modes in resonator-based metamaterial using piezoelectric wafers

Introducing designed defect(s) in locally resonant elastic metamaterials would break the periodicity and enable energy trapping in the proximity of the defect location when subjected to acoustic or vibrational excitations. In this study, a two-dimensional (2D) resonator-based defective elastic metamaterial with a hexagonal stub-plate lattice is developed to support multiple band gaps and host defect modes. Both the d ₃₁ and d ₃₆ type piezoelectric wafers are installed at the defect site to study the excitability of a variety of defect modes via modal analysis on a finite lattice. The results demonstrate that both the d ₃₁ and d ₃₆ type piezoelectric wafers can induce localized defect modes, and the d ₃₆ type piezoelectric wafer can generate a shear-dominant defect mode, which remains inaccessible with the d ₃₁ type wafer, by prioritizing face-shear deformations. All the defect modes demonstrate strong localized energy trapping to the defect site, as observed in numerical simulation and full-field dynamic response scanning experiments. Overall, this work establishes a new approach to tailor and excite defect modes in 2D vibro-elastic metamaterials, enabling opportunities in structural health monitoring and nondestructive evaluation.