Metamaterials made of exclusively metallic cut wire pairs have been experimentally demonstrated to exhibit a negative refractive index at optical frequencies. However, other related works on slightly different wire and plate pairs have not shown a negative index. In this paper, we present the analogy between previously reported S-shaped metamaterials and asymmetric cut wire pairs by a simple unifying approach. These two structures present a negative index for some geometrical configurations. Using simulations and experimental measurements in the microwave domain, we investigate the material properties of the last structure. Applying the inversion method from transmission and reflection responses, we show that a negative index is exhibited due to simultaneous negative permittivity ε and permeability μ. A negative index n is experimentally verified in a bulk prism engineered by stacking several layers of the metamaterial.
