Effects of evanescent waves in phononic crystals with linear defects
Résumé
Periodic structures with linear defects have been traditionally analyzed with the ω( k) methods with the supercell approximation. The presence of the linear defect introduces guided modes at frequencies in the band gap of the complete structure. This methodology only considers the propagating properties of the periodic system. In this work we report both theoretical predictions and experimental results considering both the evanescent and propagating waves. We obtain the evanescent properties from the complex band structures solving the inverse problem k(ω) with the Extended Plane Wave Expansion (EPWE). From the Fourier transform of the complex eigenvectors we obtain the acoustic field profile inside the system showing both the evanescent and the propagating properties. A good agreement between both the Multiple Scattering predictions and data with the EPWE simulations is obtained. The presence of evanescent waves is of fundamental interest for the design of devices based on periodicity providing a complete picture of the physical properties of the system.
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