What Quantity of Dielectric Constant in Photonic Crystals is Equivalent to that in Phononic Crystals

What quantity in a photonic crystal is equivalent to the dielectric constant in a phononic crystal

Materials or structures that have a periodic distribution of elastic constants and densities are called Phononic Crystals. Phononic crystals are a new type of functional material formed by the periodic arrangement of an elastic solid in another solid or fluid medium. By analogy with photonic crystals, it has been found that elastic waves propagating in a periodic elastic composite medium also produce an elastic wave bandgap similar to the photonic bandgap, leading to the concept of Phononic Crystals.

Elastic waves propagating in phononic crystals are prevented from propagating in a certain frequency range (bandgap) by their internal structure, while they can propagate without loss in other frequency ranges (passband). It is believed that there are two mechanisms for the generation of the bandgap in phononic crystals: the Bragg scattering type and the local **** vibration type. In the former case, the periodicity of the structure plays a dominant role, and when the wavelength of the incident elastic wave is similar to the characteristic length (lattice constant) of the structure, it will be strongly scattered by the structure. The latter is mainly dominated by the *** vibrational properties of the individual scatterers.