Broadband seismic cloaks based on gradient index metamaterial

\n\nIn this work, we propose two gradient index seismic metamaterials (GRIN SMs) for realizing the directional cloaks composed of blind holes with varying radii in a semi-infinite soil substrate for seismic Rayleigh waves. The results demonstrate that the designed cloaks can transfer more than 50% of the incident wave energy before it reaches the target buildings. More importantly, the designed cloaks have the property of wide working bandwidth from 6 Hz to 12 Hz. At certain frequencies, the attenuation of incident waves by the cloak can reach 80%. Moreover, one of cloaks composed of four Luneburg lens can achieve a multi-directional seismic cloak.\n