Eddy Current Array Tutorial
Depth of Penetration

Depth of penetration

Eddy current density does not remain constant across the depth of a material. The density is greatest at the surface and decreases exponentially with depth (the "skin effect"). The standard depth of penetration equation (shown to the right) is used to explain the penetration capability of eddy current testing, which decreases with increasing frequency, conductivity, or permeability. For a material that is both thick and uniform, the standard depth of penetration is the depth at which the eddy current density is 37% of the material surface value. To detect very shallow defects in a material, and also to measure the thickness of thin sheets, very high frequencies are used. Similarly, in order to detect subsurface defects, and to test highly conductive, magnetic, or thick materials, lower frequencies must be used.

equation

Where:
d= Standard depth of penetration (mm)
f= Test frequency (Hz)
mr= Relative magnetic permeability (dimensionless)
s= Electrical conductivity (% IACS)

Multiplexing  Flaw Detection Tutorial Next Chapter
Sorry, this page is not available in your country
Let us know what you're looking for by filling out the form below.

This site uses cookies to enhance performance, analyze traffic, and for ads measurement purposes. If you do not change your web settings, cookies will continue to be used on this website. To learn more about how we use cookies on this website, and how you can restrict our use of cookies, please review our Cookie Policy.

OK