Nonlinear guided waves (NGWs) exhibit extraordinary sensitivity to microstructural changes in materials which are often considered as damage precursors in many structural health monitoring (SHM) applications. However, these changes are usually very small at the microstructural level, thus generating weak nonlinear wave components which are prone to or even overwhelmed by other deceptive and non-damage-related nonlinear sources present in a monitoring system. This may jeopardize the practical implementation of the NGW-based SHM methodology. To tackle this problem, this paper proposes a metamaterial filter (meta-filter (MF)), in the form of a patch to be surface-mounted over the structure under inspection. The MF is designed to purify the probing waves during propagation before reaching the inspection area through tactical elimination of non-damage-related nonlinear components from the actuation. Considering different bonding conditions and the lattice symmetry of the MF, two types of bandgaps, corresponding to Bragg scattering and local resonances, alongside their respective band properties are analyzed. Time-domain finite element simulations are carried out to assess the efficacy of the MF in terms of wave purification in the context of SHM, supported by experimental validations. The designed MF is deployed in an aluminum strip to detect the material microstructural changes induced by a thermal ageing treatment. Results demonstrate the designed MF significantly enhances the detection ability of NGW-based SHM system. Both locally resonant and Bragg bandgaps can, in principle, be used for wave purification. While the former requires precise control of the bonding quality of the MF, the latter relies on symmetrical installation of the MF to ensure a reasonably wide wave filtering range. Considering variability factors in the implementation of the MF and better immunity to the nonlinearity of the bonding layers, preference is given to Bragg bandgap for NGW-based SHM applications.

非线性导波 (NGW) 对材料的微观结构变化表现出非凡的敏感性，这些变化通常被视为许多结构健康监测 (SHM) 应用中的损伤前兆。然而，这些变化在微观结构层面通常非常小，因此会产生微弱的非线性波分量，这些分量很容易受到监控系统中存在的其他欺骗性和非损坏相关非线性源的影响，甚至被淹没。这可能会危及基于 NGW 的 SHM 方法的实际实施。为了解决这个问题，本文提出了一种超材料过滤器（元过滤器（MF）），以贴片的形式安装在被检查的结构上。MF 设计用于在传播过程中净化探测波，然后再到达检测区域，通过策略性地消除驱动中与损坏无关的非线性分量。考虑到不同的键合条件和 MF 的晶格对称性，分析了两种类型的带隙，对应于布拉格散射和局部共振，以及它们各自的带特性。在实验验证的支持下，进行了时域有限元模拟，以评估 MF 在 SHM 背景下的波浪净化效果。设计的 MF 部署在铝带中，以检测由热老化处理引起的材料微观结构变化。结果表明，所设计的 MF 显着增强了基于 NGW 的 SHM 系统的检测能力。原则上，局部共振带隙和布拉格带隙都可用于波净化。前者需要精确控制中频的接合质量，后者则依靠中频的对称安装来确保合理宽的滤波范围。考虑到 MF 实施中的可变因素以及对键合层非线性的更好免疫力，基于 NGW 的 SHM 应用优先使用布拉格带隙。