Anisotropic-isotropic hybrid metamaterials for low-frequency wave attenuation

Addressing the challenge of low-frequency bandgap initiation in conventional Bragg-scattering metamaterials constrained by lattice size limitations, we present an innovative single-phase mechanical metamaterial (AZM) based on an accordion-inspired zero Poisson's ratio topological configuration. The proposed AZM architecture uniquely integrates anisotropic and isotropic domains within a periodic single-phase system, enabling low-frequency broadband Bragg-scattering bandgap at ‘subwavelength’ scales through synergistic wavelength modulation and impedance matching effects. Theoretical analysis demonstrates that the AZM unit-cell's orthogonal mechanical decoupling creates a 25-fold modulus contrast between principal axes, permitting low-frequency vibration reduction while preserving structural stiffness. The developed non-locality homogenization method reveals the underlying mechanism: anisotropic regions facilitate wavelength conversion while periodic impedance interfaces enhance Bragg-scattering, collectively opening the bandgap in the low-frequency range. Parametric studies establish clear structure-property relationships, showing bandgap initiation frequencies can be tuned to 11 Hz (P-wave) and 5 Hz (S-wave) while maintaining broadband performance across various configurations. Experimental validation confirms exceptional performance, with three-periods AZM achieving >75 % wave attenuation, featuring remarkable relative bandwidth. This work establishes a groundbreaking framework for low-frequency Bragg bandgap mechanism and pioneers a novel design paradigm, fundamentally advancing both the theoretical understanding and practical realization of Bragg metamaterials for low-frequency broadband vibration control.