Terahertz-Based Insulation Delamination Defect Inspection of Vehicle Cable Terminals

Cable terminals of the high-speed electric multiple units (EMUs) are prone to undertake insulation delamination defects due to their special operating conditions. Such a defect is difficult to identify and it may pose a great threat to the safety of the EMUs. To achieve accurate detection of insulation delamination defects, this article proposes a terahertz (THz)-based approach that combines the spectrum of the THz wave and THz imaging techniques. Specifically, a synthetic multilayer composite insulation structure with an air gap is firstly built to simulate the internal delamination defect of the cable terminal. Then THz tests in both time and frequency domains are performed on the synthetic structure. Experimental results show that the delamination defect of the multilayer insulation structure can be quickly detected by observing the absorption spectrum in the THz frequency domain. The location and geometry of the defect can be preliminarily determined by the THz imaging and then further refined through image segmentation. In addition, the thickness of the delamination defect can be quickly calculated by the THz time-domain spectrum (TDS). By combining the THz spectrum and the THz imaging information, the delamination defects are quantitatively detected for the multilayer composite structure or even for the EMU's cable terminals.