Experimental study on NDT method using electromagnetic waves

The NDT method using electromagnetic waves has strong possibility to detect defects in large structures, or large pipes. The purpose of this study is to control the electromagnetic waves of circular TM₀₁-mode near the cut-off frequency for detecting defects inside the pipes, and to obtain the information in order to develop the device for the defect detection with high speed and high accuracy. The experiment is carried out with mode converter, which can convert the rectangular TE₀₁-mode to circular TM ₀₁-mode microwaves. It is confirmed that the circular TM ₀₁-mode is converted from the rectangular TE₀₁-mode, and is generated inside the circular waveguide on some optimum conditions. It also becomes clear that the reflected wave carries a lot of information on crack width, since the obtained signal of reflected wave depends on the crack width. Experimental results strongly suggest that it is useful to apply electromagnetic waves to NDT technique.