Terahertz spectroscopy on adhesive bonds

Especially in the aerospace and automotive industries, adhesive joints continually gain importance. They hold the potential to replace conventional fastening methods by offering distinctive advantages over competing techniques, such as being cost-effective and very flexible in terms of material compatibility and surface conditions. Due to the strong demand for adhesive bonding, many technologies have been applied to study the characteristics and, especially, the integrity of adhesive bonds. If non-destructive testing is required, the choice of measuring tools narrows down considerably. In this paper, we propose terahertz time-domain spectroscopy as a non-destructive tool for the analysis of adhesive layers. We demonstrate that specialized data extraction schemes enable the contact-free determination of the adhesive layer thickness, the refractive index and the absorption coefficient from THz measurements, and show experimentally obtained data on three different material systems.