Non-Destructive Testing of Metal Backed Materials Using Reflection Mode Terahertz Spectroscopy

In this paper, we propose and demonstrate an accurate, fast and thickness independent reflection mode terahertz spectroscopy technique to determine the material parameters of the test specimen. A generalized closed form expression is derived to extract the index of refraction and thickness of the material under test. The proposed method removes the most influential error introduced in the determined index of refraction because of the mechanical measurement of the sample thickness. The method is numerically tested for two configurations, viz. metal backed specimen and air backed specimen. The extracted material parameters for both configurations are in good agreement with the reference data. The proposed technique is fast, non-destructive and self-calibrated; therefore it can find applications in automobile and aviation industries, where the materials are tested with metal at the backside of the specimen.