Thursday, 29 December 2005

Phononic Crystals

Phononic Crystal

I found an interesting article in Physics Web by Gorishnyy et al. named Sound ideas (the beautiful picture above was taken from this article). The article talks about a kind of crystal, named a phononic crystal, that can be constructed in such a way to create specific "band gaps" for waves travelling in this solid. This means that you can control which frequency cannot propagate in the crystal, creating, for example, materials that become isolators for particular sounds or mechanical waves.

The band gaps are created by carefull design of the crystals allowing a control of the dispersion relation, the relation between frequency and wave number, in phonons, which are quantized modes of vibration in a solid. This quantization of vibrational modes comes from a treatment using the machinery of quantum mechanics and is a very important mechanism that, among other things, influence the heat condictivity of materials. For a short introduction to the theory of elementary excitations in solids see Elementary Excitations in Solids : Lectures on Phonons, Electrons, and Plasmons by David Pines.

Phononic crystals may have a lot of interesting technological applications described in detail inside the article, in the words of the authors

"Phononic crystals will provide researchers in acoustics and ultrasonics with new components that offer the same level of control over sound that mirrors and lenses provide over light."

Over my desk:

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