Abstract-Nondestructive imaging of hidden defects in aircraft sandwich composites using terahertz time-domain spectroscopy

Qiang Wang, Xinyi Li, Tianying Chang, Jin Zhang, Lingyu Liu, Hongbin Zhou, Jinpeng Bai,



https://www.sciencedirect.com/science/article/pii/S1350449518306091

Aircraft sandwich composites are superior to ordinary composites and have been largely used in the manufacture of military aircraft. This study attempts to investigate the efficacy of terahertz (THz) time-domain spectroscopy (TDS) imaging technology in detecting hidden defects in aircraft glass fiber (GF) sandwich composites. The defects of various sizes, such as debonding, delamination, and multi-delamination, at different depths in GF A-sandwich structure composites with foam core, C-sandwich structure composites with honeycomb core, and sheet-to-sheet cementing structure composites were evaluated. The THz frequency-domain amplitude and time-domain amplitude imaging algorithms were used to visualize the defects simulated by ultrathin double-layer Teflon inserts. And the suitable image processing methods which include wavelet-based fusion and multiscale edge representation were employed. With a combination of high-resolution THz C-scan and B-scan imaging, both the horizontal size and location, and the vertical depth and thickness of the defects were obtained in three dimensions. This study experimentally demonstrated that THz imaging technology can clearly detect various hidden defects in aircraft GF sandwich composites through reflection or transmission imaging mode.

Abstract-Efficient Terahertz Wide-Angle NUFFT-Based Inverse Synthetic Aperture Imaging Considering Spherical Wavefront

Jingkun Gao, Bin Deng, Yuliang Qin, Hongqiang Wang, Xiang Li

http://www.mdpi.com/1424-8220/16/12/2120

An efficient wide-angle inverse synthetic aperture imaging method considering the spherical wavefront effects and suitable for the terahertz band is presented. Firstly, the echo signal model under spherical wave assumption is established, and the detailed wavefront curvature compensation method accelerated by 1D fast Fourier transform (FFT) is discussed. Then, to speed up the reconstruction procedure, the fast Gaussian gridding (FGG)-based nonuniform FFT (NUFFT) is employed to focus the image. Finally, proof-of-principle experiments are carried out and the results are compared with the ones obtained by the convolution back-projection (CBP) algorithm. The results demonstrate the effectiveness and the efficiency of the presented method. This imaging method can be directly used in the field of nondestructive detection and can also be used to provide a solution for the calculation of the far-field RCSs (Radar Cross Section) of targets in the terahertz regime.