Feasibility study on the detection of corrosion of a cable metal shield using terahertz imaging

Time-domain imaging and spectroscopic measurements were carried out using terahertz (THz) light in order to examine the feasibility of non-destructive corrosion diagnosis of a metallic shielding layer in a power cable. At first, the absorbance of the THz light was measured for various corroded copper, namely copper oxide, basic copper carbonate, and copper chloride. As a result, both basic copper carbonate and copper chloride were found to exhibit absorption clear and strong enough for the imaging. Next, a non-corroded copper plate and one of the corroded plates were placed on a metal plate without making an open interspace, and the THz light was irradiated and scanned in order to get two-dimensional images. When the plate is corroded to form either basic copper carbonate or copper chloride, the intensity of reflected light becomes small compared with the non-corroded copper plate. The reason for this seems that the THz light was scattered more at the surface of the corroded copper plate and was absorbed more by the corrosion. These phenomena indicate that non-destructive diagnosis to detect corrosion of a shield metal is possible.