What is the lift-off effect in MPI?

The lift-off effect in Magnetic Particle Inspection (MPI) refers to the phenomenon where magnetic particles do not effectively cling to the surface of a test object due to a gap or distance between the magnetic field source and the surface being inspected. This can occur when there are rough surfaces, coatings, or other obstructions that prevent the magnetic field from penetrating the surface adequately.

When the lift-off effect is present, it can hinder defect detection because the magnetic particles may not cluster around defects effectively. Instead, they can become misaligned or dispersed, leading to a failure to indicate the presence of flaws that are in close proximity to the surface. As a result, inspectors may overlook critical defects that would otherwise be detected if the particles were properly aligned and concentrated around those areas.

This highlights the importance of understanding the lift-off effect when performing MPI, as it directly impacts the reliability and effectiveness of the inspection results. In contrast, while magnetic alignment, successful inspections, and background noise can all play roles in the MPI process, they do not directly describe the detrimental impact that lift-off can have on detecting surface defects.