Mohammed Nadzri, N. I., K. A. Sidek, and A. F. Ismail. “Biometric Recognition for Twins Inconsideration of Age Variability Using PPG Signals”. Journal of Telecommunication, Electronic and Computer Engineering (JTEC), vol. 10, no. 1-5, Feb. 2018, pp. 97-100, https://jtec.utem.edu.my/jtec/article/view/3638.