Description
Anti-resonant guidance has become an important concept for understanding and engineering wave confinement in structured media. In acoustics, recent work has begun to explore antiresonant confinement in cylindrical waveguides in Brillouin scattering experiments, but existing treatments have thus far focused on single-layer structures. In this work, we provide a general method for analysing elastic leakage in multilayer cylindrical anti-resonant waveguides. We formulate a transfer-matrix method for concentric multilayer elastic cylinders in which the mode is described by a complex effective index that arises as a parameter in a nonlinear eigenvalue problem. We compute elastic leaky modes in multilayer cylindrical waveguides and use the developed method to investigate both modal dispersion and radiative leakage of these structures. We find that there are two mechanisms for guidance in these leaky structures: first, the mode can be guided via strong reflections at particular angles from a double elastic layer, in an analogous way to the Brewster angle in electromagnetism. Second, acoustic guidance can arise from multiple Bragg reflections from the layers. We treated outgoing radiation conditions analytically via a nonlinear eigenvalue formulation. We find that Bragg-guided modes exhibit exponentially reduced leakage with increasing layer number. We demonstrate the method for each of these types of leaky modes and compute the dependence of leakage loss on the number of layers and on the geometry of the guiding structure.
| I am the presenting author | No |
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| If you are not the presenting author, please give the presenting author's name: | Chris G. Poulton |