A Subregion Fusion Method for Guided Waves and Electromechanical Impedance-Based Damage Imaging

Structural health monitoring (SHM) is critical for ensuring the long-term, high-reliability service of aircraft structures and systems. Accurate damage localization is a key aspect of SHM technique development. Guided wave (GW) and electromechanical impedance (EMI) are two widely used SHM techniques. GW is effective for large-area damage detection, while EMI offers high damage monitoring sensitivity near sensors. However, both traditional GW and EMI methods suffer from regions of reduced damage monitoring sensitivity, which may result in regions of low detectability and undermine reliable damage detection. Missed detections may allow minor damage to grow rapidly, potentially leading to catastrophic structural failure. To address this issue, this article proposes a subregion fusion strategy that leverages the complementary strengths of GW and EMI. The monitoring area is divided into near and far subregions based on the damage monitoring sensitivity range of the EMI damage index (DI). In the near subregion, GW and EMI probabilistic imaging results are fused to eliminate regions of low detectability. In the far subregion, GW probabilistic imaging is enhanced using a distribution coefficient derived from the EMI DI. Experiments on aluminum and composite plates show that the newly proposed fusion method reduces average localization errors by 32% and 39% compared to traditional GW probabilistic imaging, and by 53% and 54% compared to EMI probabilistic imaging, respectively. These results demonstrate that the proposed fusion strategy effectively eliminates regions of low detectability and improves damage localization accuracy across the entire monitoring area. With its strong extendibility and potential for continuous improvement, the proposed subregion fusion imaging method is expected to serve as a valuable tool for long-term structural integrity assurance in complex and mission-critical systems, including thin-walled aerospace components such as reusable spacecraft, rocket fuel tanks, and engine shells, as well as thin-walled civil and industrial structures such as pressure vessels, large oil and chemical storage tanks, and thin-walled steel structural elements.