Asymmetric geometry creates a negative index metamaterial in the microwave regime

A metamaterial, with an asymmetric geometry, characterized simultaneously by a double negative permittivity and permeability is introduced. We show that tuning a left-handed symmetric bilayer metamaterial recently proposed by Ozbay et al. towards an asymmetric monolayer in the microwave regime does not suppress the left-handed behavior at normal incidence. The bilayer structure is transformed step by step firstly into a monolayer symmetric structure which does not exhibit any left-handed behavior and finally into an asymmetric monolayer material where a left-handed behavior reappears at normal incidence.