Tunable acoustic absorbers with periodical micro-perforations having varying pore shapesShuwei Ren, Xuewei Liu, Junqing Gong, Yufan Tang, Fengxian Xin, Lixi Huang and Tian Jian LuEPL, 120 4 (2017) 44001DOI: https://doi.org/10.1209/0295-5075/120/44001