Magnetic flux leakage measurement setup for defect detection

AbstractThis paper describes a potential technique to detect medium size defects in ferromagnetic specimen by using rather inexpensive but highly sensitive sensors based on the giant magneto resistive effect (GMR) [1]. The sensor effect is used very effectively in ultra high density magnetic recording devices and might thus prove effective in the material testing business, too. These sensors measure the magnetic flux leakage near the surface of a magneto-conductive object. In order to test their potential initial tests were performed and their results evaluated. For this survey some test specimen were made by intentionally causing some imperfections (actually small drilled holes, or some surface scratches, etc.) in an otherwise homogeneous and isotropic ferromagnetic specimen. In order to obtain the distribution of the magnetic flux leakage, the surface of the test specimen was mechanically scanned. Preliminary results are very encouraging since we could show that even small blemishes can easily be detected this way