Spectroscopic study of terahertz reflection and transmission properties of carbon-fiber-reinforced plastic composites

Carbon-fiber-reinforced plastic (CFRP) composites are widely used in aerospace and concrete structure reinforcement due to their high strength and light weight. Terahertz (THz) time-domain spectroscopy is an attractive tool for defect inspection in CFRP composites. In order to improve THz nondestructive testing of CFRP composites, we have carried out systematic investigations of THz reflection and transmission properties of CFRP. Unidirectional CFRP composites with different thicknesses are measured with polarization directions 0 deg to 90 deg with respect to the fiber direction, in both reflection and transmission modes. As shown in the experiments, CFRP composites are electrically conducting and therefore exhibit a high THz reflectivity. In addition, CFRP composites have polarization-dependent reflectivity and transmissivity for THz radiation. The reflected THz power in the case of parallel polarization is nearly 1.8 times higher than for perpendicular polarization. At the same time, in the transmission of THz wave, a CFRP acts as a Fabry-Perot cavity resulting from multiple internal reflections from the CFRP-air interfaces. Moreover, from the measured data, we extract the refractive index and absorption coefficient of CFRP composites in the THz frequency range. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.