Locally resonant metamaterials utilizing dynamic directional amplification: An application for seismic mitigation

Locally resonant metamaterials (LRMs), with unit-cells exhibiting local resonance, pre-sent unique wave propagation properties as a result of their spatial periodicity. However, these structures present certain limitations in designing systems with wide bandgaps in the low-frequency range. Aiming to confront the main practical challenges encountered in such cases, including heavy parasitic oscillating masses, a simple dynamic directional amplification (DDA) mechanism is proposed. This amplifier is designed to comprise the same mass and use the same damping element of a reference two-dimensional (2D) mass-in-mass metamaterial. Thus, no increase in the structure's mass or vis-cous damping is required. The proposed DDA can be realized by imposing kinematic constraints to the structure's degrees of freedom (DoFs), hence increasing inertia to the desired direction of motion. A discrete element lattice model based on mass, stiffness, and damping elements, is used to establish dispersion behavior and frequency response. The numerical results of an indicative case study indi-cate significant improvements and advantages over the reference LRM, such as broader bandgaps and increased damping ratio. Finally, a conceptual design of a metabarrier based on this concept indicates the usage of this mechanism in potential applications, such as seismic wave mitigation and protection of structures.