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A subwavelength seismic metamaterial (SM) consisting of a three-component SM plate (SMP) and a half space is proposed to attenuate ultra-low frequency seismic surface waves. The design concept and models are verified first by lab-scale experiments on the SM consisting of a two-component SMP and a half space. Then, we calculate the band structures of one-dimensional and two-dimensional subwavelength SMs and evaluate their ability to attenuate Rayleigh waves. A wide ultra-low frequency bandgap can be found, and the Rayleigh waves are deflected by the subwavelength SM and converted into bulk waves in the frequency range of this bandgap. When the number of unit cells of the subwavelength SM is sufficient, the transmission distance and deflection angle of the Rayleigh waves are constant at the same frequency. This discovery is expected to open up the possibility of pragmatic seismic protection for large nuclear power plants, ancient buildings, and metropolitan areas. [ABSTRACT FROM AUTHOR]

A meta-slab composed of subunits with graded thicknesses is proposed for spatially separating the zeroth- and first-order acoustic waveguide modes according to the generalized Snell's law. The phase velocity for the first-order mode depends on the waveguide thickness, whereas that for the zeroth-order mode does not. This enables the required phase-shift gradients of the meta-slab to be obtained for spatially separating the two waveguide modes. To design the meta-slab, analytic solutions are derived for the transmission coefficients and phase shifts of the incident acoustic waves with the two modes propagating through the subunits. Numerical simulations with transient finite-element analyses are implemented to demonstrate the propagation of the two waveguide modes. Sinusoidal signal and tone-burst excitations are applied in the analyses. The latter case shows that the two waveguide modes can be successfully separated in space by the designed meta-slab. [ABSTRACT FROM AUTHOR]

We explore a seismic metasurface (SMS) design to control Rayleigh wave propagation for the earthquake resistance of critical buildings. An SMS is designed by assembling an array of soil mound units with different inclination angles to mold an accurate phase shift of the incoming seismic Rayleigh waves. We propose three SMSs to realize the three effects of forming Rayleigh wave fields: beam splitting, arbitrary convex trajectory bending, and wavefront focusing. The results demonstrate that the designed SMSs can remove more than 90% of the incident wave energy before it reaches the target buildings. Our compact SMSs, which feature low cost and are easy to implement, constitute an active earthquake-resistance method in civil engineering and are potentially useful in applications such as energy collection, nondestructive testing, and signal modulation for surface waves. [ABSTRACT FROM AUTHOR]

A novel seismic metamaterial plate consisting of two common building materials, which has the advantages of simple structure and easy to realize, is proposed. The seismic metamaterial plate creates a wide bandgap with a relative bandwidth of 1. Using numerical simulation, the bandgap properties of the metamaterial plate both in a free space and on a half space are studied and it is found that the wide bandgap of the free plate is kept even if in half space. Using scaled (1:30) experiments under 1 g conditions and simulations, we study the transmission spectrum under the surface waves incident on the seismic metamaterial plate and verify that it has a good attenuation effect in the corresponding frequency range. This work paves the way to the design of seismic metamaterials allowing an unparalleled control of surface wave propagation. [ABSTRACT FROM AUTHOR]