Non-destructive measurement of thickness and refractive index of multilayer coating on metal substrate

Automotive coating plays an important role in car industry. They protect the car bodies from various aggressive weathering and mechanical deformations. Although many techniques have been developed for car coating, there is still a demand for non-destructive characterization of multilayer coatings. Therefore, research on new measurement methods is still ongoing. In this paper, we investigate thin coating layers on metal substrate using THz time-domain spectroscopy (THz-TDS). We are able to apply existing algorithm but in reflection method using THz-TDS to distinguish the thickness as thin as 20mm of individual layers.