Terahertz time domain characterization method of the adhesive layer uniformity in multiple bonding structures

Multilayer bonding structure is widely used in aerospace field, and its bonding strength is the key factor to ensure engineering safety. Different terahertz time-domain spectroscopy parameters such as time-of-flight, energy and amplitude were used to characterize the uniformity of the adhesive layer of multilayer bonding structure, and then evaluate the bonding quality of multilayer bonding structure materials. The uniformity of the adhesive layer was qualitatively analyzed by the terahertz time-domain spectroscopy time-of-flight imaging method. The relative standard deviations of flight time of four experimental samples are 8.78%, 8.09%, 7.30% and 9.57% respectively; Using the energy integration information of terahertz time-domain spectroscopy, the kurtosis and skewness of the energy integration curve were used to qualitatively analyze the uniformity of the adhesive layer. The energy standard deviations of four experimental samples were 0.95, 0.9, 0.71 and 1.01, respectively; In addition, according to the amplitude characteristic information of terahertz time-domain spectroscopy, the uniformity of adhesive layer was quantitatively characterized by amplitude dispersion coefficient. The results show that the time-of-flight, energy integral and amplitude of terahertz time-domain spectroscopy can be use to quantitatively evaluate the adhesive layer uniformity of multi-layer adhesive structures. This method can provide a reliable means for evaluating the adhesive strength of multi-layer adhesive structures.