Haroun, K. M., A. A. M. Yagob, and M. D. Abd Allah. “Derivation of Klein – Gordon Equation for Frictional Medium”. American Scientific Research Journal for Engineering, Technology, and Sciences, vol. 38, no. 1, Nov. 2017, pp. 1-6, https://asrjetsjournal.org/index.php/American_Scientific_Journal/article/view/3526.