FDTD-based internal moisture damp inspection for vehicle cable terminal in terahertz domain

The vehicle cable terminal stands as a critical insulation component crucial for the safe functioning of high-speed railways, frequently susceptible to moisture-related issues during operational use. Addressing internal defects within electrical composite insulation structures like vehicle cable terminals, the utilization of terahertz non-destructive testing technology has garnered substantial interest owing to its distinct advantages over conventional detection methodologies, notably in terms of safety, efficiency, non-invasive nature, and its capacity for both quantitative and qualitative defect characterization. This investigation employs the finite difference time domain (FDTD) technique to simulate and assess a pre-moisture-defected model of the vehicle cable terminal, juxtaposed against experimental findings derived from a terahertz time-domain spectroscopy (THz-TDS) apparatus. Initially, the optical parameters essential for the medium are discerned using a THz-TDS system and subsequently integrated into the FDTD system to formulate and analyze the moisture-defected terminal model. Subsequent to this, an experimental specimen is crafted based on the simulation model, and the moisture-defected model is evaluated employing the THz-TDS system to procure both time-domain and frequency-domain spectra of the defective sample. Finally, the characterization of defects within the vehicle cable terminal is executed by juxtaposing and analyzing the time-domain and frequency-domain outcomes obtained from both simulation and experimental methodologies. The outcomes signify a notable concordance between the simulated and experimental spectra, underscoring the efficacy of the FDTD method in effectively assessing internal moisture within vehicle cable terminals.