Finite Difference Time Domain Modeling and Inversion of Internal Delamination Defects in Vehicle Cable Terminal in Terahertz Band

To address the gap in simulating internal defects within composite insulation structures in the terahertz domain for vehicle cable terminals, this article proposes a finite difference time domain (FDTD) modeling and inversion method based on terahertz time-domain measurement results. First, based on the actual structure of the vehicle cable terminal and simplified equivalents, a three-layer composite insulation structure was constructed, and a prefabricated 1.35 mm delamination defect sample between the stress tube and the ethylene propylene rubber (EPR) layer was prepared. Then, the time-domain characteristics of the sample were tested and analyzed using a terahertz time-domain spectroscopy (THz-TDS) system. Based on this, the optical parameters of insulating materials within the terahertz frequency range of the model are extracted using a transmission THz-TDS system, and the Debye model is employed to fit and optimize the measured parameters. Finally, FDTD simulations and inversions for internal delamination defects in vehicle cable terminals were conducted within the terahertz frequency range. The results demonstrate a high agreement between the proposed FDTD-based defect modeling and inversion method and actual experimental results. Under unknown optical parameters of the test sample, combining THz-TDS experimental results with FDTD numerical modeling enables the inversion and quantitative characterization of internal delamination defects in vehicle cable terminals.