Broadband seismic cloaks based on gradient index metamaterial Zepei Tang, Yuexin Zhang, Zhiang Linghu, Hongwu Yang, Pai Peng, Fengming Liu and Qiujiao Du EPL, 147 6 (2024) 66001 Published online: 30 September 2024 DOI: 10.1209/0295-5075/ad7057