What does "lift-off" refer to in the context of Eddy Current Testing?

In the context of Eddy Current Testing, "lift-off" specifically refers to the distance between the surface of the test piece and the probe. This is a critical measurement because it affects the interaction between the probe's electromagnetic field and the conductive material being tested. When there is an increase in lift-off due to the separation between the probe and the test surface, it can diminish the induced eddy currents, leading to variations in the signal received by the testing device.

Understanding lift-off is essential for accurate measurements, as it can lead to misleading indications if not taken into account. In practice, maintaining a consistent lift-off is important for minimizing signal variation and ensuring reliable assessment of the material's properties, such as thickness, conductivity, and the presence of defects.