What does a shift in impedance during an ET inspection indicate?

In an eddy current inspection, a shift in impedance typically indicates a change in the electrical properties of the material being tested. This shift can occur due to various factors, one of the most significant being the presence of a defect within the specimen. When a defect, such as a crack or inclusions, alters the material's conductivity or permeability, it affects how the eddy currents flow, thereby changing the impedance measured by the inspection setup.

This change is critical to identifying potential flaws within the material, as it provides insight into the integrity and quality of the specimen. The inspection relies on the relationship between the impedance response and the structural variations in the material, helping inspectors to locate and characterize any defects present. Recognizing these impedance shifts is a key aspect of interpreting eddy current data and confirming the condition of the inspected object.