Terahertz spectroscopic study of aeronautical composite matrix resins with different dielectric properties

This study was to investigate the spectral characteristics of aeronautical composite matrix resins (ACMRs) that differ in dielectric properties in terahertz frequency range. Terahertz time-domain spectroscopy was employed to examine the spectral absorption and dielectric dispersion characteristics of five ACMRs of three major types, namely, epoxy resins 3238A and BA9916, cyanate ester (CE) resin 9915, and bismaleimide (BMI) resins QY8911 and QY9611, between 0.2 THz to 1.6 THz. The refractive index n, the absorption coefficient α and the real part ε′ and imaginary part ε″ of the dielectric constant of each resin were calculated. On this basis, the relaxation process of dipoles was theoretically analyzed using the Debye model. The results showed that, ε″ of each epoxy resin was higher than that of each BMI resin, while ε″ of the CE resin was the lowest. The CE resins had the lowest ε′ and exhibited the highest and most stable dielectric performance, followed by the BMI resins, whereas the epoxy resins exhibited fluctuating and slightly less stable dielectric performance. This study gives, for the first time, the basic parameters of five ACMRs (epoxy, CE and BMI resins) in terahertz frequency range, and provides an important reference for THz nondestructive testing of aeronautical composites.