Non-destructive inspection
If the magnetized specimen has any defect blocking magnetic flux found in its surface or surface area, a magnetic field leaks from the point. Both sides of the defected part have poles, and the defected part seems to be a small magnet, generating a magnetic field in the space. When magnetic particles are sprayed to the space, they are magnetized to have poles, and are attached to the defected part. By looking at the dense pattern of the magnetic particles, it is possible to measure the defected part and size of the specimen.
