Category: Wave Functional Materials

Evanescent waves can play an important role in meta-materials.  The most famous example is the Perfect Lens invented by J B Pendry. The lens, a flat slab of material with both permittivity and permeability being minus one, can attain a sub-wavelength resolution by amplifying the evanescent wave within the lens. However, for evanescent waves with bigger and bigger transverse wave vectors, it is expected that the microstructure starts to become important so that the physics deviates from the local effective medium description of the meta-material.

In order to investigate the effect of microstructure, a dipolar model is employed to model the metamaterial so that on one hand we can derive the local effective medium directly. On the other hand, a complete ( , ) dispersion diagram can be obtained with microstructure taken into consideration. As a result, the complete dispersion diagram converges to the local effective medium description only near the Brillouin zone center.

Continue reading The effect of microstructure on meta-materials

It has been demonstrated that light bends into the “wrong” quadrant when impinging from a normal medium to a double negative (DNG) medium. A DNG medium in electromagnetism is regarded as an effectively homogeneous medium having both negative permittivity and negative permeability. Here, we prove that such a concept can apply also to other kinds of classical waves. In particular, for acoustic waves, if we want sound to bend into the “wrong” quadrant after hitting an interface between air and the DNG medium, it turns out that we need a double negativity in both density and bulk modulus for the DNG medium.

Continue reading Double negativity in acoustic waves