Free eddy current testing calculators: standard depth of penetration, phase lag, limit frequency and f/fg normalized frequency, conductivity conversion between %IACS, MS/m and resistivity, and coil fill factor for tube and rod inspection.
Calculates the standard depth of penetration (δ), the depth where eddy current density falls to 37% (1/e) of the surface value, from frequency, resistivity, and relative permeability. Using δ (mm) = 50 √(ρ / f·μr) with ρ in μΩ·cm and f in Hz. Higher frequency, higher conductivity, or higher permeability all reduce penetration. Effective depth of penetration is about three standard depths.
Calculates the limit frequency (fg) for a rod or tube from conductivity, permeability, and diameter using fg = 5066 / (σ·μr·d²), then gives the normalized frequency f/fg for your test frequency. Because every nonmagnetic part plots on the same normalized impedance curve, f/fg tells you where you are operating regardless of material or size. Around f/fg = 6 to 7 conductivity and diameter signals are nearly 90° apart for the best separation; higher f/fg concentrates current at the surface for crack detection.
"I have a 1 cm aluminum rod and a 60 kHz coil" to "I'm at f/fg ≈ 4, so I'm in the conductivity-sorting region, and I should raise frequency if I want surface crack sensitivity."
These calculators or for education purposes only please verify results ans consult with NDT professionals for critical applications.