A Novel Rectangular Vertical Probe With A Conductive Shell For Eddy Current Testing

Eddy current testing is one of electromagnetic methods that are suitable for the inspection of conductive materials. Compared to regular flat coil, rectangular vertical coil can induce a more uniform eddy current distribution in the plate. With other advantages such as directional properties and less sensitive to lift-off variations, the rectangular vertical coil is considered superior to the flat one in certain applications. However, the eddy current of the conventional rectangular vertical coil is comparatively low as the weak coupling between the coil and the conducting plate. It is challenging to achieve high sensitivity and accuracy for the detective sensor such as GMR or pickup coil. To increase the coupling, a novel probe with a conductive shell is proposed in this study. With the proposed probe, a conductive loop can be formed by the test plate and shell when the shell is in good contact with the test plate during the test. And the conductive loop can effectively increase the coupling and the induced current in the test plate. A simulation model is set up with the finite element method to verify the performance of the designed probe. The results show that the eddy current density in the plate is improved by the proposed probe. When a defect is present, the change of the magnetic flux density and equivalent reactance of the proposed probe are more obvious than the conventional rectangular vertical coil. This improvement is also validated by the experiment of equivalent reactance measurement.