Simple examples of perfectly invisible and trapped modes in waveguides

Summary We consider the propagation of waves in a waveguide with Neumann boundary conditions. We work at low wavenumber with only one propagating mode in the leads, all the other modes being evanescent. We assume that the waveguide is symmetric with respect to an axis orthogonal to the longitudinal...

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Bibliographic Details
Published in:Quarterly journal of mechanics and applied mathematics 2018-08, Vol.71 (3), p.297-315
Main Authors: Chesnel, L, Pagneux, V
Format: Article
Language:English
Subjects:
Analysis of PDEs
Mathematics
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Summary:Summary We consider the propagation of waves in a waveguide with Neumann boundary conditions. We work at low wavenumber with only one propagating mode in the leads, all the other modes being evanescent. We assume that the waveguide is symmetric with respect to an axis orthogonal to the longitudinal direction and is endowed with a branch of height $L$ whose width coincides with the wavelength of the propagating modes. In this setting, tuning the parameter $L$, we prove the existence of simple geometries where the transmission coefficient is equal to one (perfect invisibility). We also show that these geometries, for possibly different values of $L$, support so-called trapped modes (non-zero solutions of finite energy of the homogeneous problem) associated with eigenvalues embedded in the continuous spectrum.
ISSN:0033-5614
1464-3855
DOI:10.1093/qjmam/hby006