Coating Thickness Characterization of Composite Materials Using Terahertz Waves

Recently, terahertz ray imaging has emerged as one of the most promising new powerful nondestructive evaluation (NDE) techniques for the area applications. In this study, a new time-domain spectroscopy system was utilized for measuring the coating thickness on CFRP composite laminates. Extensive experimental measurements in reflection mode were made to map out the T-ray images. Also, the refractive index was estimated based on the electromagnetic properties. The CFRP composite laminates were observed in reflection mode and limitations will be discussed in the T-ray processing. By using these characterized material properties, the characteristics was successfully demonstrated for T-ray behavior propagating through the Shim Stock films for acquiring the refractive index. The T-ray technique has been developed for the measurement of the thickness of the Shim Stock films and the coating thickness on CFRP composites. Good results have been obtained in tests made on the thickness of the standard film samples with the coating thickness ranging from around hundreds of μm.