抄録
Terahertz waves are effective for detection of delamination of dielectric coatings applied onto a metal surface. In most cases, the thickness of the air gap which results from delamination is much smaller than the spatial width of the terahertz pulse, so the reflections from the upper and lower boundaries of the air gap, and the multiple reflections within the air gap are not temporally resolved. The reflection of the terahertz pulse was calculated based on an impulse response model, which included the effects of multiple reflection. The calculation results were compared with the experimental results in the case of reflection from a three-layer structure consisting of a polyethylene plate, air gap, and metal plate. The results showed that an air gap with a thickness of about 30 µm can detected, even when the lower limit of the time-resolved measurement was 120 µm.
