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**Electromagnetic wave scattering from locally perturbed periodic inhomogeneous layers.**
*(English)*
Zbl 1479.35851

Summary: We consider the scattering problem for locally perturbed periodic penetrable dielectric layers, which is formulated in terms of the full vector-valued time-harmonic Maxwell’s equations. By assuming a non-periodic right-hand side, or, a perturbation in the permittivity, one cannot reduce the problem to one periodic cell in the classical way. In this article we present a method to solve such scattering problems. For that, we apply the Floquet-Bloch transform to derive a coupled family of quasi-periodic problems and solve the individual quasi-periodic problems by combining some standard methods with technical calculations. This approach works as long as we stay away from the singularities in the quasi-periodicity of the Calderon operator, which we use for the boundary condition. The challenge is to prove the unique existence of the solutions for the quasi-periodicities inside the one-dimensional set for which the quasi-periodic differential operator is singular. The idea to tackle this problem is to construct a limit solution by letting the quasi-periodicity converge to a singularity while decomposing the quasi-periodic differential operator using the Sherman-Morrison-Woodbury formula. Additionally, we show regularity results of the Floquet-Bloch transformed solution to the perturbed problem on the unbounded domain with respect to the quasi-periodicity mode. These results, i.e., contribute to a numerical method to approximate the solution to the unbounded domain problem, which we will describe in a forthcoming work.

### MSC:

35Q61 | Maxwell equations |

35A01 | Existence problems for PDEs: global existence, local existence, non-existence |

35A02 | Uniqueness problems for PDEs: global uniqueness, local uniqueness, non-uniqueness |

35A22 | Transform methods (e.g., integral transforms) applied to PDEs |

35B65 | Smoothness and regularity of solutions to PDEs |

35B20 | Perturbations in context of PDEs |

78A45 | Diffraction, scattering |

78A48 | Composite media; random media in optics and electromagnetic theory |