Double-gradient seismic metamaterials with zero-frequency bandgap characteristic in a layered soil medium

Abstract

Seismic metamaterials (SMs) are an artificially composite material designed within the sub-wavelength range. To attenuate low-frequency seismic surface waves, a metamaterial structural unit composed of a lead core and an auxetic foam coating layer was proposed; the higher impedance ratio results in the creation of a zero-frequency bandgap under layered soil conditions. To broaden the attenuation zone (AZ), double-gradient seismic metamaterials (DGSMs) were designed. The frequency domain analysis indicates that the attenuation area covering the range of 0–10 Hz is 89.8%. Through displacement-field analysis, the attenuation mechanism of DGSM on specific frequency surface waves can be fully explained. Finally, Taft seismic wave excitation is input for time history analysis, and the acceleration amplitude within 0–2 Hz decreases by 58.6%, which verifies the effectiveness of DGSMs in attenuation of low-frequency seismic waves.