Resonant-type Luneburg lens for broadband low-frequency focusing Liuxian Zhao, Xuxu Zhuang, Hao Guo, Chuanxing Bi and Zhaoyong Sun EPL, 145 4 (2024) 40001 Published online: 14 March 2024 DOI: 10.1209/0295-5075/ad2871