A rational framework for dynamic homogenization at finite wavelengths and frequencies

Bojan B. Guzina, Shixu Meng, Othman Oudghiri-Idrissi

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Abstract

In this study, we establish an inclusive paradigm for the homogenization of scalar wave motion in periodic media (including the source term) at finite frequencies and wavenumbers spanning the first Brillouin zone. We take the eigenvalue problem for the unit cell of periodicity as a point of departure, and we consider the projection of germane Bloch wave function onto a suitable eigenfunction as descriptor of effective wave motion. For generality the finite wavenumber, finite frequency homogenization is pursued in Rd via second-order asymptotic expansion about the apexes of 'wavenumber quadrants' comprising the first Brillouin zone, at frequencies near given (acoustic or optical) dispersion branch. We also consider the junctures of dispersion branches and 'dense' clusters thereof, where the asymptotic analysis reveals several distinct regimes driven by the parity and symmetries of the germane eigenfunction basis. In the case of junctures, one of these asymptotic regimes is shown to describe the so-called Dirac points that are relevant to the phenomenon of topological insulation. On the other hand, the effective model for nearby solution branches is found to invariably entail a Dirac-like system of equations that describes the interacting dispersion surfaces as 'blunted cones'. For all cases considered, the effective description turns out to admit the same general framework, with differences largely being limited to (i) the eigenfunction basis, (ii) the reference cell of medium periodicity, and (iii) the wavenumber-frequency scaling law underpinning the asymptotic expansion. We illustrate the analytical developments by several examples, including Green's function near the edge of a band gap and clusters of nearby dispersion surfaces.

Original languageEnglish (US)
Article number20180547
JournalProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume475
Issue number2223
DOIs
StatePublished - Mar 1 2019

Bibliographical note

Funding Information:
This study was partially supported through the endowed Shimizu Professorship. S.M. was partially supported by NSF grant no. DMS-1439786 while in residence at ICERM Brown University during autumn 2017 and AFOSR award no. FA9550-18-1-0131.

Publisher Copyright:
© 2019 The Authors.

Keywords

  • Dirac points
  • Dynamic homogenization
  • Finite frequency
  • Finite wavenumber
  • Nearby eigenvalues
  • Waves in periodic media

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