Exceptional points (EPs) are degeneracies of two or more natural modes of open systems, which lead to unusual wave phenomena. Despite the robustness against imperfections of spatial EPs, they are less studied relative to temporal EPs, particularly in elastodynamics. However, elastic waves exhibit features not found in sound and light, which have proven useful for forming spatial EPs. Here, we harness these features to tune the coalescence of three eigenmodes in the Bloch spectrum of planar elastic laminates. We show that these third-order EPs give rise to : anomalous transmitted waves with zero axial group velocity and finite transmittance. These modes, which were first reported in optics and required three-dimensional laminates, are achieved here in a planar setting thanks to elastodynamics tensorial structure, and expand the toolbox for elastic wave shaping.

中文翻译：

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平面弹性层合板中的三阶异常点和冻结模式

例外点（EP）是开放系统的两个或多个自然模式的简并，这会导致不寻常的波动现象。尽管空间 EP 具有针对缺陷的鲁棒性，但相对于时间 EP，它们的研究较少，特别是在弹性动力学方面。然而，弹性波表现出声音和光中没有的特征，这些特征已被证明对于形成空间 EP 很有用。在这里，我们利用这些特征来调整平面弹性层压板的布洛赫谱中三种本征模的合并。我们证明这些三阶 EP 会产生：具有零轴向群速度和有限透射率的反常透射波。这些模式首次在光学领域报道并需要三维层压板，借助弹性动力学张量结构在平面设置中实现，并扩展了弹性波整形的工具箱。