Electromagnetic Testing Eddy Current in Brief

How far do the eddy currents penetrate into a test piece?
The strength of the response from a flaw is greatest at the surface of the
material being tested, and decreases with depth into the material. The
"Standard depth of penetration" is mathematically defined as the point when
the eddy current is 1/e or 37% of its surface value. The "effective depth of
penetration" is defined as three times the standard depth of penetration,
where the eddy current has fallen to about 3% of its surface value. At this
depth there is no effective impact on the eddy current and a valid inspection is
not feasible.
Penetration depth will:
- Decrease with an increase in conductivity
- Decrease with an increase in permeability
- Decrease with an increase in frequency
Charlie Chong/ Fion Zhang