NDT of the Shape of a Thin 3D Slit on the Metal Surface by Millimeter Waves

As the basis of the evaluation of nature cracks, a millimeter wave method to evaluate the shape of a thin 3D slit on the metal surface is demonstrated. An open-ended coaxial line sensor was proposed to improve the spatial resolution of the measurement. The amplitude of the reflection coefficient that is associated with the dimensions of the slit is measured by scanning the specimen in the direction perpendicular to the detected slit. A characteristic signal corresponding to the detected slit was obtained and, was used to evaluate the depth of the slit.