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Localization of high-frequency waves propagating in a locally periodic medium

Published online by Cambridge University Press:  01 October 2010

G. Allaire
Affiliation:
Centre de Mathématiques Appliquées, École Polytechnique, 91128 Palaiseau, France (gregoire.allaire@polytechnique.fr)
L. Friz
Affiliation:
Departamento de Ciencias Básicas, Facultad de Ciencias, Universidad del Bío-Bío, Avenida Andrés Bello s/n, Casilla 447, Chillán, Chile (lfriz@roble.fdo-may.ubiobio.cl)

Abstract

We study the homogenization and localization of high-frequency waves in a locally periodic media with period ε. We consider initial data that are localized Bloch-wave packets, i.e. that are the product of a fast oscillating Bloch wave at a given frequency ξ and of a smooth envelope function whose support is concentrated at a point x with length scale . We assume that (ξ, x) is a stationary point in the phase space of the Hamiltonian λ(ξ, x), i.e. of the corresponding Bloch eigenvalue. Upon rescaling at size we prove that the solution of the wave equation is approximately the sum of two terms with opposite phases which are the product of the oscillating Bloch wave and of two limit envelope functions which are the solution of two Schrödinger type equations with quadratic potential. Furthermore, if the full Hessian of the Hamiltonian λ(ξ, x) is positive definite, then localization takes place in the sense that the spectrum of each homogenized Schrödinger equation is made of a countable sequence of finite multiplicity eigenvalues with exponentially decaying eigenfunctions.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2010

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