The change in impedance of an eddy current test coil due to variations in test part characteristics is usually analyzed as a change in:

In eddy current testing, the analysis typically revolves around how changes in the characteristics of the test part, such as conductivity, permeability, and thickness, affect the response of the eddy current test system. This response is fundamentally characterized by variations in both the signal's amplitude and phase.

When an eddy current flows through a coil positioned near a conductive material, any variations in the material's properties lead to changes in the impedance of the coil. This impedance is not constant and depends on how the eddy currents induced by the probe interact with the test material.

The change in signal amplitude is indicative of the strength of the eddy currents generated, which directly relates to the conductive properties of the test part. As conductivity increases, for instance, the amplitude of the detected signal increases, while changes in material thickness can affect both amplitude and phase delay.

The phase shift is another key aspect because it reflects the relative changes in the reactance and resistance within the system due to the material's properties. Hence, tracking both the amplitude and the phase provides comprehensive insight into the anomalies or characteristics of the material being tested.

This approach is central to the analysis of eddy current testing and allows testers to identify defects, changes in material properties, and other relevant information