Non-destructive Inspection Method for Defects in Epoxy Resin by using THz Wave

In this paper, a non-destructive inspection method by using THz waves will be discussed to detect defects in epoxy resin, which is widely used as an insulating material in power equipment. Fundamental data were obtained, such as the absorption rate of THz waves in epoxy resin. We tested epoxy resin samples with different kinds of internal defects: voids, metallic fragments, resin burrs. Sample thicknesses were also varied. Defect imaging of these samples showed that the reflection intensity of THz waves greatly differed depending on defect type. This suggests that THz intensity is useful for distinguishing defect types.