Ahmad, A. ., R. Ruzairi, P. W. Han, A. K. . Ismail, M. S. . Abdul Manaf, N. . Ahmad, E. J. . Mohammad, Y. . Abdul Wahab, Z. . Zakaria, and K. S. Chan. “Gold Purity Determination Using Ultrasonic Wave: A Review”. Journal of Tomography System and Sensor Application, vol. 6, no. 1, June 2023, pp. 52-60, http://tssa.my/index.php/jtssa/article/view/218.