Electromagnetic wave in terahertz frequency range (THz wave) is getting an increasing attention in many engineering applications, since THz wave has following characteristics. (1) THz wave has outstanding transmittance for many kinds of materials except for metals and water, (2) THz wave is safe for human body, and (3) THz wave can be used for material identification utilizing its fingerprint absorption spectrum. In this paper, a nondestructive evaluation technique based on THz wave imaging is developed for coating materials. Terahertz time-domain spectroscopy (THz-TDS) system is employed for evaluating transmittance of corrosion protection coating and reflectance of underneath substrate material, to investigate the feasibility of proposed nondestructive evaluation technique.
