What does a change in impedance indicate during Eddy Current Testing?

A change in impedance during Eddy Current Testing indicates a variation in the material's properties. Impedance in this context is a measure of how much the material resists or impedes the flow of alternating current (AC) created by the test probe. When the properties of the material change—such as its conductivity, permeability, or thickness—this will affect the way the eddy currents behave, resulting in a change in impedance.

For instance, if there is a flaw, such as a crack or corrosion, or if the material is composed of a different alloy, the interaction between the magnetic field generated by the probe and the material will alter. As this occurs, the eddy currents will either be enhanced or diminished, which leads to a measurable change in impedance. This is a critical aspect of Eddy Current Testing, as it allows testers to identify inconsistencies and potential defects within the material, ensuring safety and reliability in various applications.