| Negative refractive index material (NIM) is usually treated as a homogeneous medium characterized by a negative permittivity and a negative permeability. They are in fact derived from resonances and as such, their physical properties cannot be exactly identical to an effective homogeneous medium. To understand the importance of the underlying resonances, I constructed models in which negative permittivity and negative permeability can be derived in the long wavelength limit as accurate as one likes within the framework, and then I examined the slab focusing effect to unveil the subtle difference between a truly homogenous left-handed medium and that an effective medium carrying an underlying sub-wavelength structure. I showed that an effective medium that carries hidden microstructures can still serve as a "superlens", but the divergences disappeared and there will also be a natural limit of resolution, as dictated by the details of the underlying resonances (i.e. perfect lens is not possible). The superlens effect is also shown to be a near-field effect. I also showed for the first time that it is possible to have a "double negative" acoustic medium, which is the analog of left-handed electromagnetic medium. The generalization from EM wave to acoustic wave is in fact non-trivial. Such a medium is a composite which has negative mass density and negative bulk modulus, or in other words, it moves to the right when you push to the left and expands when it is compressed. We will see that the double negative acoustic medium may also be realized in practice. I also showed that by mixing NIM with ordinary materials, we can get a new type of photonic band gap which is scale-invariant and insensitive to disorder. Results are presented for 1D and generalized to 3D. |
