Lu Wang, Mengjun Wang, Kanglong Zhang, Wenjie Cui, Hongxing Zheng, and Erping Li. “Three-Dimensional Spherical-Shaped UPML for FDTD With Cubic Lattices”. Applied Computational Electromagnetics Society Journal (ACES), vol. 34, no. 03, Mar. 2019, pp. 475-82, https://journals.riverpublishers.com/index.php/ACES/article/view/8573.