Evaluation of uncertainty in handheld terahertz spectroscopy

Abstract

Advances in terahertz spectroscopy have shown it to be an effective tool for the inspection of polymers and ceramics in laboratory environments. Furthermore, recent work has shown promise that terahertz reflectance spectroscopy may be effectively applied to surface characterization of CMCs and PMCs to investigate chemical changes resulting from thermal degradation. However, even under tightly controlled laboratory conditions, various sources of uncertainty such as surface variability, ambient atmospheric conditions, as well as measurement errors within the system will be present. The analysis of measurement uncertainty is further complicated by the fact that reflectance spectra are constituted by the nonlinear relationship between the dielectric spectra and the reflectance spectra, thereby making model calibration more difficult as compared to transmission and absorbance spectroscopy. As inspections transition from laboratory to field-level applications sources of uncertainty must be considered to properly assess the health of a material with any means of statistical significance. In this study, spectra from terahertz spectroscopy systems are investigated to assess the variation in measurement uncertainty. By characterizing the uncertainty variation, recommendations are proposed for improving inspection procedures in both laboratory and field-level NDE.