arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.15162math.APcs.NAmath.NA
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周期介质中Dirichlet或Neumann不相容波的谱渐近性

On the spectral asymptotics of waves in periodic media with Dirichlet or Neumann exclusions

Othman Oudghiri-Idrissi, Bojan B. Guzina, Shixu Meng

摘要:

我们考虑均匀化的标量波动方程在周期性介质中在有限的波数和频率,重点是连续的特点是:(a)任意布拉维格$\mathbb{R}^d$,$d\!\geqslant\!2$,和(b)排除,即“空隙”,受到同质(诺依曼或狄利克雷)边界条件。利用布洛赫波展开,我们追求这一目标,通过渐近分析具有“光谱距离”从一个给定的波数本征频率对(在第一布里渊区)作为扰动参数。然后,我们通过标量波场到周期性晶胞的布洛赫本征函数上的投影引入有效波动,在谱邻域的原点处进行评估。一般来说,我们占的波动方程中的源项的存在下,我们认为-在一个给定的波数-孤立的,重复的,和附近的特征值的一般情况下。通过这种方式,我们得到了一个调色板的有效模型,具有波和Dirac型的行为,其适用性是由本地带结构和本征函数的基础。在所有的频谱制度,我们追求的均匀化描述至少一阶的扩展,具有渐近校正的均匀化布洛赫波算子和均匀化源项。本质上,这样的框架提供了一个方便的平台,在超材料和声子晶体中的各种波动现象的综合。所提出的均匀化框架,说明了渐近近似的色散关系的(i)Kagome晶格具有六角诺依曼排除,和(ii)“钉扎”正方形晶格与圆形Dirichlet排除。我们完成的数值描绘的分析发展,通过研究由于一个偶极类源项附近的带隙的边缘作用的可果美晶格的响应。

英文摘要:

We consider homogenization of the scalar wave equation in periodic media at finite wavenumbers and frequencies, with the focus on continua characterized by: (a) arbitrary Bravais lattice in $\mathbb{R}^d$, $d\!\geqslant\!2$, and (b) exclusions i.e. "voids" that are subject to homogenous (Neumann or Dirichlet) boundary conditions. Making use of the Bloch wave expansion, we pursue this goal via asymptotic ansatz featuring the "spectral distance" from a given wavenumber-eigenfrequency pair (within the first Brillouin zone) as the perturbation parameter. We then introduce the effective wave motion via projection(s) of the scalar wavefield onto the Bloch eigenfunction(s) for the unit cell of periodicity, evaluated at the origin of a spectral neighborhood. For generality, we account for the presence of the source term in the wave equation and we consider -- at a given wavenumber -- generic cases of isolated, repeated, and nearby eigenvalues. In this way we obtain a palette of effective models, featuring both wave- and Dirac-type behaviors, whose applicability is controlled by the local band structure and eigenfunction basis. In all spectral regimes, we pursue the homogenized description up to at least first order of expansion, featuring asymptotic corrections of the homogenized Bloch-wave operator and the homogenized source term. Inherently, such framework provides a convenient platform for the synthesis of a wide range of wave phenomena in metamaterials and phononic crystals. The proposed homogenization framework is illustrated by approximating asymptotically the dispersion relationships for (i) Kagome lattice featuring hexagonal Neumann exclusions, and (ii) "pinned" square lattice with circular Dirichlet exclusions. We complete the numerical portrayal of analytical developments by studying the response of a Kagome lattice due to a dipole-like source term acting near the edge of a band gap.

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