Effectively negatively refractive material made of negative-permittivity and negative-permeability bilayer

Using effective medium approximation (EMA) method, we investigate the effective permittivity and permeability of the bilayer composed of negative-permittivity layer and negative-permeability layer. Analytic expressions of all six elements of the effective permittivity and permeability tensors are derived. It is found that these elements have different signs and values at different frequency regions. To one's interest, negative refraction can be realized in the bilayer, which may provide an easier way to fabricate negatively refractive materials. Moreover, we discuss the EMA method with both small |klz|dl|klz|dl and large |klz|dl|klz|dl. In addition, we also investigate the excitation of the surface polaritons at the interfaces of the bilayer. Like negatively refractive materials, the bilayer can also amplify evanescent waves owing to the excitation of the surface polaritons at the interfaces, which can confirm the equivalence between the bilayer and a slab of negatively refractive material.