What does an increase in impedance during Eddy Current Testing usually indicate?

An increase in impedance during Eddy Current Testing typically indicates the presence of a defect or a change in material properties. Eddy Current Testing relies on the principle of electromagnetic induction, where electrical currents are induced into the material being tested and produce a magnetic field. If there is a change in the material, such as a crack, inclusion, or variation in conductivity, it will cause a disruption in the flow of eddy currents. This disruption results in an increase in impedance, which can be detected by the testing equipment.

Understanding the relationship between impedance and material properties is crucial for interpreting testing results. Defects such as cracks or gaps alter both the geometry and the conductivity of the material, leading to a measurable increase in the measured impedance. This characteristic makes Eddy Current Testing a valuable tool for detecting surface and near-surface defects in conductive materials.