Magnetic Non-destructive Testing

The technology operating principle is shown in Figure 1. The magnetic field source is a permanent magnet and generates magnetic flux in the test object. In the absence of flaws, magnetic field is almost completely inside the ferromagnetic test object and the magnetic field sensor (Hall sensor in Figure 1) detects absence of magnetic field. In the presence of flaws, a local change in the test object magnetic properties occurs; magnetic field tries to go round the area with a low magnetic permeability, and therefore partly comes to the surface, generating dispersion fields. The magnetic field sensor registers these fields. Thus, information about the presence of magnetic field in the sensor indicates the presence of a flaw under the sensor.