The paper investigates the existence of interfacial (Stoneley-type) acoustic waves localised at the internal boundary between two semi-infinite superlattices which are adjoined with each other to form one-dimensional phononic bicrystal. Each superlattice is a periodic sequence of perfectly bonded homogeneous and/or functionally graded layers of general anisotropy. Given any asymmetric arrangement of unit cells (periods) of superlattices, it is found that the maximum number of interfacial waves, which can emerge at a fixed tangential wavenumber for the frequency varying within a stopband, is three for the lowest stopband and six for any upper stopband. Moreover, we show that this number of three or six waves in the lowest or upper stopband, is actually the maximum for the number of waves occurring per stopband in a given bicrystal plus their number in the "complementary" bicrystal, which is obtained by swapping upper and lower superlattices of the initial one (so that both bicrystals have the same band structure). An example is provided demonstrating attainability of this upper bound, i.e. the existence of six interfacial waves in a stopband. The results obtained under no assumptions regarding the material anisotropy are also specified to the case of monoclinic symmetry leading to acoustic mode decoupling.

中文翻译：

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各向异性周期超晶格中的斯通利型波

该论文研究了位于两个半无限超晶格之间的内部边界处的界面（Stoneley 型）声波的存在，这些超晶格彼此相邻以形成一维声子双晶。每个超晶格是具有一般各向异性的完美结合的均匀和/或功能梯度层的周期性序列。给定超晶格的晶胞（周期）的任何不对称排列，发现在阻带内变化的频率的固定切向波数处可以出现的界面波的最大数量对于最低阻带为三个，对于任何阻带为六个上阻带。此外，我们表明在最低或最高阻带中的三个或六个波的数量，实际上是给定双晶中每个阻带出现的波数的最大值加上它们在“互补”双晶中的数量，这是通过交换初始双晶的上下超晶格获得的（这样两个双晶都具有相同的能带结构） . 提供了一个示例来证明该上限的可达性，即阻带中存在六个界面波。在不考虑材料各向异性的情况下获得的结果也适用于导致声模式解耦的单斜对称情况。阻带中存在六个界面波。在不考虑材料各向异性的情况下获得的结果也适用于导致声模式解耦的单斜对称情况。阻带中存在六个界面波。在不考虑材料各向异性的情况下获得的结果也适用于导致声模式解耦的单斜对称情况。