Three-dimensional imaging technique based on multi-channel spectral amplitude superposition in the impact-echo method: Methodology and engineering application

Most imaging techniques based on the Impact-Echo (IE) method remain limited to two-dimensional (2D) imaging, which can only characterize defect distribution along a single plane and often fail to accurately identify complex defects. To identify defects inside concrete structures more accurately and intuitively using the impact echo method, this study proposes a three-dimensional (3D) imaging approach based on the superposition of spectral amplitudes from multi-channel IE signals. By acquiring data from multiple spatial positions and summing the frequency-domain amplitudes, the proposed method significantly reduces the interference caused by the “spherical effect” commonly observed in conventional IE imaging. The effects of defect size and embedment depth on imaging accuracy of the proposed method were investigated through numerical simulations and validated via in-situ tests on a real structure. Results indicate that the proposed method performs optimally in constructing images with large, shallow defects, while its accuracy decreases for small defects located at greater depths. The findings provide both theoretical insight and practical reference for the advancement of 3D visualization techniques in the nondestructive evaluation of concrete structures. • Enables high-resolution 3D visualization of internal voids in concrete using impact-echo data fusion. • The dimensionality of traditional 2D impact-echo imaging is extended to 3D for volumetric defect reconstruction. • The proposed method effectively suppresses the ring/spherical artifact common in conventional SIBIE imaging. • The effect of defect size and embedment depth on 3D imaging accuracy is systematically analyzed. • Multiple 2D slices are extracted from reconstructed volumes to validate spatial localization precision.