Figure 4-5. Relative Magnitude and Distribution of Eddy Currents in
Conductive Material of High and Low Permeabilities.
In a part, such as sheet material, in which the thickness is less than the effective depth of penetration, the overall
electromagnetic field is not zero at the back surface. As the back surface gets closer to the front surface, the overall
field at the back surface increases; and as the back surface gets further from the front surface the overall field decreases.
This provides a mechanism for thickness gauging of thin materials. Furthermore, a material of either lower or higher
conductivity at the far side will change the magnitude and distribution of the eddy currents as shown in Figure 4-6.
This provides a means for thickness gauging of thin, conductive coatings on substrates that are either more or less
conductive than the coating.
Figure 4-6. Distribution of Eddy Currents in Thin Conductors Backed by
Materials of Different Conductivitys.