How is the lift-off effect remedied in MPI?

The lift-off effect in Magnetic Particle Inspection (MPI) occurs when there is a separation between the magnetic particles and the surface of the material being inspected, which can lead to an incomplete indication of defects. This effect can obscure the detection of surface and near-surface discontinuities, making it crucial to manage effectively.

Adjusting the magnetic field strength and orientation directly addresses the lift-off effect by ensuring that the magnetic field is strong enough to overcome the distance between the magnetic particles and the defect. By optimizing the magnetic field, it enhances the magnetic particle attraction to the surface, allowing the particles to effectively indicate the presence of any discontinuities without the barrier of lift-off. This strategy is particularly effective during inspections of complex geometries or surfaces with varied profiles, where lift-off may be more pronounced.

In contrast, increasing the contrast of magnetic particles, cleaning the surface, or using different types of magnetic particles may help to some extent with visibility or general effectiveness of the inspection, but these measures do not specifically counteract the lift-off effect itself. Therefore, adjusting the magnetic field strength and orientation remains the most direct and effective method of remedying this issue during MPI.