Rotational scanning–based observation augmentation for overdetermined reconstruction of the CCSI inverse problem

Coplanar Capacitive Scanning Imaging (CCSI) is a promising nondestructive testing (NDT) technique. However, due to the open diffusion characteristic of the fringe electric field and the limited measurement information, its inverse problem is usually severely ill-posed, which affects the quality of defect image reconstruction. To address this issue, this study proposes a measurement and linear system augmentation method based on single-electrode-pair rotational scanning, building upon the previously established forward and inverse problem model of CCSI. Under the assumption that the unknown medium distribution remains unchanged, the scanning observations obtained at different rotation angles are incorporated into a unified inverse problem framework, thereby augmenting the observation equations of the original linear system and providing additional independent constraints for image reconstruction. Simulation and experimental results demonstrate that the proposed rotational scanning augmentation method can improve the rank characteristics and numerical stability of the system matrix, while enhancing the reconstruction quality, structural consistency, and artifact suppression capability for irregular defect distributions. With the increase in angular information involved in reconstruction, the recovered defect images show an overall continuous improvement trend. This study provides a new modeling and measurement strategy for alleviating the ill-posedness of the CCSI inverse problem and improving the imaging performance of coplanar capacitive NDT.