Figure 4-10. Relative Intensity of Eddy Currents with Variations in Lift-Off.
When an encircling coil is used to inspect a cylindrically shaped part, the degree of magnetic coupling is dependent
upon the difference between the internal diameter of the coil and the external diameter of the part. This effect is
termed fill-factor (see Figure 4-11) and is designated by the ratio of the squares of the diameters as follows:
Figure 4-11. Fill-Factor.