Influence of electric field direction of terahertz radiation on composite materials

Terahertz waves (T-ray) for the non-destructive evaluation were investigated on composite materials. The modalities of the T-ray radiation used were time domain spectroscopy and continuous wave for composites. The composite materials are composed of non-conducting polymeric composites and carbon fiber composites. T-ray signals in the time domain spectroscopy mode resembles that of ultrasound; however, unlike ultrasound, T-ray pulse can detect a crack hidden behind a larger crack (shadow effect). Thick glass fiber reinforced polymer laminates containing double-saw slots was demonstrated. Also, in carbon composites the penetration of T-ray waves was investigated in order to detect flaws is strongly affected by the angle between the electric field vector of the terahertz waves and the intervening fiber directions. Other composites tested in this study include both solid laminates and honeycomb sandwiches. The defects and anomalies investigated by T-ray were foreign material inclusions, simulated disbond and delamination, mechanical impact damage, heat damage, and water or hydraulic fluid ingression. The intensive characterization of T-ray for the non-destructive evaluation of composites are being discussed.