Over several decades, electromechanical impedance (EMI) measurements have been employed as a basis for structural health monitoring and damage detection. Traditionally, Root-mean-squared-deviation (RMSD) and Cross-correlation (XCORR) based metrics have been used to interpret EMI measurements for damage assessment. These tools, although helpful and widely used, were not designed with the idea to assess changes in EMI to underlying physical changes incurred by damage. The authors propose leveraging vector fitting (VF), a rational function approximation technique, to estimate the poles of the underlying system, and consequently, the modal parameters which have a physical connection to the underlying model of a system. Shifts in natural frequencies, as an effect of changes in the pole location, can be attributed to changes in a structure undergoing damage. With VF, tracking changes between measurements of damaged and pristine structures is physically more intuitive unlike when using traditional metrics, making it ideal for informed post-processing. Alternative methods to VF exist in the literature (e.g., Least Square Complex Frequency-domain (LSCF) estimation, adaptive Antoulas--Anderson (AAA), Rational Krylov Fitting (RKFIT)). The authors demonstrate that VF is better suited for EMI-based structural health monitoring for the following reasons: 1. VF is more accurate at high frequency, 2. VF estimates complex conjugate stable pole pairs, close to the actual poles of the system, and 3. VF can capture critical information missed by other approaches and present it in a condensed form. Thus, using the selected technique for interpreting high-frequency EMI measurements for structural health monitoring is proposed. A set of representative case studies is presented to show the benefits of VF for damage detection and diagnosis.

翻译：数十年来，机电阻抗（EMI）测量一直被用作结构健康监测和损伤检测的基础。传统上，基于均方根偏差（RMSD）和互相关（XCORR）的度量指标被用于解释EMI测量以进行损伤评估。这些工具虽然有用且被广泛使用，但其设计初衷并非用于评估EMI变化与损伤引起的底层物理变化之间的关联。作者提出利用矢量拟合（VF）——一种有理函数逼近技术——来估计底层系统的极点，进而获得与系统底层模型具有物理关联的模态参数。作为极点位置变化的结果，固有频率的偏移可归因于结构损伤引起的变化。与使用传统度量指标相比，通过VF追踪损伤结构与完好结构测量值之间的变化在物理意义上更为直观，这使其成为理想的信息化后处理工具。文献中虽存在VF的替代方法（例如最小二乘复频域（LSCF）估计、自适应Antoulas--Anderson（AAA）算法、有理Krylov拟合（RKFIT）），但作者证明VF更适合基于EMI的结构健康监测，原因如下：1. VF在高频下更精确；2. VF能估计接近系统实际极点的复共轭稳定极点对；3. VF能以凝练形式捕捉其他方法遗漏的关键信息。因此，本文建议采用该选定技术来解释用于结构健康监测的高频EMI测量。通过一组代表性案例研究，展示了VF在损伤检测与诊断方面的优势。