Khaeruddin, “Boundary Element Analysis of Acoustic Wave Problems in Functionally Graded Materials”, IJIE, vol. 18, no. 4, pp. 139–156, Jun. 2026, Accessed: Jul. 23, 2026. [Online]. Available: https://penerbit.uthm.edu.my/ojs/index.php/ijie/article/view/23170