Robust low-frequency elastic wave transport in lightweight hexagonal lattice metamaterials

Abstract Lightweight structures with efficient vibration and noise attenuation capabilities are of great significance for modern engineering applications. Recent advancements have significantly expanded the working frequency range of topological phononic crystal plates. Nevertheless, the design of topological microstructures that enable larger areas for wave transport remains a critical challenge. This study proposes a lightweight hexagonal lattice elastic metamaterial that enables topologically protected transport of low-frequency elastic waves while maintaining structural efficiency. By tuning the geometric parameters of the composite unit cell, a double Dirac degeneracy is formed at the Γ point of the Brillouin zone, leading to a controllable topological phase transition. The band inversion between p - and d -state modes is achieved by breaking the spatial symmetry of the system, resulting in the opening of a nontrivial bandgap. A supercell composed of topologically trivial and nontrivial domains is further constructed to reveal the robust interface state in the bandgap. Further, a finite-sized metamaterial specimen was fabricated, and vibration transmission tests were also conducted to validate the numerical model. The experimental results confirm the existence of low-loss, unidirectional elastic wave propagation along the designed interface, in excellent agreement with the simulated field distributions. This study provides a new strategy for realizing lightweight and low-frequency broadband vibration isolation, while also offering a promising pathway for efficient energy harvesting.