Radial seismic metamaterials with ultra-low fre-quency broadband characteristics
The metamaterials applications for protecting buildings by manipulating seismic waves, such as nuclear power plants and ancient buildings protection, have garnered considerable attention. A new type of ultra-low frequency broadband radial seismic metamaterial (RSM) has been proposed in this paper. Contrary to traditional seismic metamaterials(SM), the proposed RSMs are arranged with radially periodic steel rings embedded in the soil. The propagation characteristics of seismic Lamb waves and surface waves in RSM are investigated. Additionally, the dispersion relations and displacement vector fields are determined by using the finite element method. As the numerical discussion, lower and wider bandgap characteristics for seismic Lamb waves and surface waves are shown in RSM in contrast to the SM. For seismic Lamb waves, the RSM with rectangular cross-section exhibits the beginning frequency of bandgaps as low as 1.6 Hz, with a bandwidth ratio of 81.27% increased by 65.33% relative to the SM in the range of 0.1-50 Hz, which is produced by the coupling between the seismic Lamb modes and local resonance; for surface waves, RSM also has a low-frequency broadband and larger NRBW(57.5%) than the SM with the same lattice constant and filling fraction, which is caused by coupling of the overall axial resonance and Rayleigh waves mode. Furthermore, the influence of geometric parameters and material properties of RSM on bandgap characteristics is obtained. Finally, a 3D full-scale finite period model, which involves in-plane and out-of-plane modes, is designed to demonstrate the earthquake shielding performance of RSM. The proposed shielding approach could provide a better alternative in the field of seismology and related areas of ultra-low frequency vibration damping or blast protection.