Terahertz Characterization of Cable Terminal: A Debye-PSO Modeling and Inversion Approach

Terahertz (THz) wave propagation in insulation materials of cable terminal is governed by their optical and dielectric properties. This study investigated these properties in cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) cable terminal materials using THz time-domain spectroscopy (THz-TDS) in the 0.2–1.5 THz range. We measured and analyzed four key parameters: refractive index n₁(ω), absorption coefficient α₁(ω), and the real and imaginary parts of the dielectric constant [ϵ₁′(ω) and ϵ₁′′(ω)] across six insulation materials, including XLPE, EPR, stress tube, and umbrella skirt. The Debye model was employed to theoretically analyze dipole relaxation processes, with particle swarm optimization (PSO) applied to overcome the limitations of traditional nonlinear fitting methods in the dispersion model. Our comprehensive approach combined experimental measurements, theoretical modeling, and optimization techniques to establish the fundamental THz band parameters for these materials. The results revealed distinct correlations between the materials' microstructure and their electromagnetic properties. This article provides essential theoretical foundations and reference data for THz-based detection of internal defects in cable terminals. Additionally, the microstructural-level analysis of electromagnetic property variations offers new insights into evaluating cable terminal aging states using THz technology.