Terahertz imaging of iron powder in low density polyethylene sheets

If powder of iron is included in the insulation of a polymer-insulated cable during its manufacturing process, breakdown or a water tree would be triggered from there. In this study, we mixed powder of iron into a sheet of low-density polyethylene and measured spatial distributions of absorption at terahertz (THz) frequencies. As a result, it has become clear that the absorption increases in the whole range from 0.5 to 5.0 THz at the places where the powder exists, even if the sheet is covered with an opaque carbon-black-loaded polyethylene sheet.