Joshua M. Kast, and Atef Z. Elsherbeni. “Simulation of a Nonlinear Frequency Multiplier Using the FDTD Technique”. The Applied Computational Electromagnetics Society Journal (ACES), vol. 35, no. 11, Nov. 2020, pp. 1426-7, https://journals.riverpublishers.com/index.php/ACES/article/view/7629.