An a priori error estimate for the finite element modelling of electromagnetic waves interacting with a periodic diffraction grating

Natacha Lord, Anthony Mulholland

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An a priori error estimate using a so called α,β- periodic transformation to study electromagnetic waves in a periodic diffraction grating is derived. It has been reported for single scattering that there is an instability in numerical methods for high wavenumbers. To address this problem, the analytical solution of the scattering problem when the domain is scatterer free and an unknown function called the α,β-quasi periodic solution are used to transform the associated Helmholtz problem. The well-posedness of the resulting continuous problem is analysed before approximating its solution using a finite element discretization. To guarantee the uniqueness of this approximate solution, an a priori error estimate is derived. Finally, numerical results are presented that suggest that the α,β-quasi periodic method converges at a far lower number of degrees of freedom than the α,0-quasi periodic method reported previously; especially for high wavenumbers. This is particularly true when the incident wave only undergoes a small perturbation because of the presence of the scatterer.
Original languageEnglish
Pages (from-to)1187–1205
Number of pages19
JournalMathematical Methods in the Applied Sciences
Issue number10
Early online date13 Sep 2012
Publication statusPublished - 15 Jul 2013


  • periodic diffraction grating;
  • helmholtz
  • scattering
  • finite element
  • priori error estimate
  • electromagnetic waves

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