N. T. Tung, P. V. Hoai, N. T. Binh, L. V. Hong, V. D. Lam and Y. P. Lee, {Demonstrate the Double Negative Behavior of Metamaterial Using the Effective Medium Theory, Comm. Phys. 20 (2012) 83. DOI: https://doi.org/10.15625/0868-3166/20/1/2009.