Proposal of inspection method for rear side defect in steel plate using electromagnetic force vibration

It is important to detect the rear side corrosion and defect of steel plates used in large structures, etc. Generally, the radiation transmission inspection method or the ultrasonic flaw detection tests are widely used for the detection of a defect in steel. However, the former inspection method is required a long inspection time and a lot of cost for equipment. In the latter method, the contact catalysts such as water or grease are required and the surface of the steel plate needs to be polished. In this research, the detection method of the rear side defect in the steel plate by applying vibration due to electromagnetic force and measuring its vibration is proposed. The proposed inspection sensor consists of a permanent magnet, an alternating excitation coil using a steady exciting frequency, and a vibration sensor. The rear side defect in the steel plate is evaluated by the excitation frequency component of the measured vibration intensity using the vibration sensor. The vibration distribution by the electromagnetic force in the steel plate with and without the defect is evaluated by the electromagnetic 3D-FEM analysis considering the non-linearity of the magnetic characteristics and the displacement 3D-FEM analysis.