Imaging of Permeability Change of Steel Plate Using Rectangular Wave Eddy Current Testing

Abstract

Magnetic materials are used for the iron cores of transformers, reactors, and rotating machines. The reduction of the iron loss of the iron core can reduce the loss of these electrical equipment and contribute to energy saving. Therefore, it is important to quantitatively evaluate the magnetic properties of magnetic materials. On the other hand, the eddy current test is widely used to detect changes in electromagnetic characteristics such as conductivity and magnetic permeability without the specimen contacting the sensor. In this paper, we image and quantitatively evaluate changes in the magnetic properties of steel sheets using rectangular wave eddy current testing (RECT). First, we basically verify whether RECT can detect the spatial magnetic property change of the steel sheet due to the magnetization of the permanent magnet. The result demonstrates that RECT is useful image and quantify the spatial magnetic property change. Second, the effect of magnetization on the signal obtained by RECT is examined by changing the intensity of DC magnetic field, and electromagnetic field simulation based on the finite element method is also conducted to calculate the magnetic permeability distribution inside the steel sheet when a DC magnetic field is applied and validate the experimental results. The experimental result demonstrates that the signal depends on the intensity of the DC magnetic field, and the simulation result supports the experimental result.