抄録
Terahertz (THz) waves are electromagnetic waves in the frequency region 100GHz-10THz, and are useful for nondestructive testing of dielectric materials, such as polymers, plastics, and ceramics. In this report, application of THz waves to inspection of thermal barrier coating (TBC), corrosion evaluation and detection of rust under paint, and improvement of spatial resolution in THz imaging is presented. TBC is applied to high temperature components in gas turbines, and consists of a ceramic topcoat and a metallic bondcoat. THz waves were shown to be effective for measuring the topcoat thickness, which is an important factor which determines the thermal resistivity. Early stages of corrosion of metal substrates covered with paint are difficult to detect by visual inspection, but could be visualized using THz waves. In imaging using THz waves, the spatial resolution is mainly limited by the effective spot size. Frequency filtering of THz waves and combination with image processing techniques were found to be effective for improving the spatial resolution. This was demonstrated in THz imaging of an IC card.
