Issues in design of one-dimensional metamaterials for seismic protection

Metamaterials provide an unprecedented solution for seismic hazard mitigation by blocking seismic wave transmission. This paper investigates the wave attenuation capability of one-dimensional binary seismic metamaterials. Variations in the bandgaps of metamaterials are studied analytically with different material combinations. Results indicate that large contrasts in mass densities and wave velocities between the two constituent materials are desirable in consideration of gap width and central frequency, and increasing the contrast in mass density is relatively more effective. Reducing the filling ratio of the soft and light material is also beneficial to seismic wave attenuation. However, several practical challenges are also highlighted. For example, attenuation of low frequency waves inevitably leads to low global stiffness of seismic metamaterials because the use of soft constituent material is indispensable. Despite enhancement of the attenuation effect in the whole frequency range, material damping weakens the band structure. In addition, the vibration in front of the metamaterial is amplified to a certain degree due to wave reflections. These may present several practical conundrums in the application of seismic metamaterials.