Terahertz scanning techniques for paint thickness on CFRP composite solid laminates

Abstract

Terahertz ray (T-ray) scanning applications are promising tools. The use of T-ray for nondestructive evaluation was investigated on composite materials. In this characterization procedure, electromagnetic properties, such as the refractive index, were analyzed. The estimates of properties are in good agreement with known data. We successfully demonstrated the characteristics of T-ray propagating through Carbon fiber-reinforced plastic (CFRP) composites to acquire the refractive index by using the characterized material properties. A T-ray technique was developed for measuring paint thickness on CFRP laminates. Good results were obtained from tests performed on standard paint samples with thickness starting from approximately 100 μm. The method was based on reflection mode measurement with time of flight. Another method developed for measuring paint thickness using resonance frequencies was utilized to determine paint thickness on composite laminates. The paint thickness deduced from resonance frequencies agrees well with the result obtained directly from time-domain echoes.