2018 Volume 104 Issue 12 Pages 784-790
The signal of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, ultrasonic and electromagnetic techniques are used. Magnetization is modulated with the radio frequency (RF) of irradiated ultrasonic waves through magnetomechanical coupling. The signal amplitude of ASEM waves is determined by the magnitude of piezomagnetic phenomenon which is acoustically excited locally. The induced RF magnetic fields are detected by a resonant coil antenna. Here, we applied the ASEM method to detect defects on thin steel sheets. If there is a defect in a steel sheet at a constant magnetization, magnetic flux density distribution around the defect is different from that of sound area. This difference can be detected through the ASEM method. Using a small antenna, 5 mm in diameter and 10 mm at liftoff, we can detect a 0.1 mm through hole in a steel sheet at 0.16 mm in thickness.