What does "particle mobility" refer to in MPT?

In Magnetic Particle Testing (MPT), "particle mobility" specifically refers to the ability of magnetic particles to move freely in a magnetic field and respond to magnetic forces. This concept is crucial because the effectiveness of MPT relies on the particles being able to appropriately distribute themselves around any discontinuities or defects in a material. When the magnetic field is applied, particles that are highly mobile will be able to align themselves with the magnetic flux lines and accumulate at areas of flux leakage, indicating a defect, whereas particles that are less mobile may not respond as effectively, leading to missed indications.

This ability to move and redistribute is fundamental for achieving reliable and accurate testing results. Factors such as particle size, shape, and material composition can influence particle mobility, but it fundamentally pertains to how freely the particles can move in the presence of a magnetic field.