What term describes the effect of changing electromagnetic coupling between a test specimen and a probe coil?

The term that describes the effect of changing electromagnetic coupling between a test specimen and a probe coil is "Lift off." Lift off refers to the distance between the probe coil and the test specimen. As this distance changes, the strength of the electromagnetic coupling also varies. For instance, when the probe is closer to the specimen, stronger eddy currents are induced, resulting in a greater signal response. Conversely, as the lift-off increases, the coupling weakens, leading to a reduced signal. This phenomenon is critical in Eddy Current Testing because it helps in identifying surface conditions and material properties, as variations in lift-off can influence the readings significantly.

Understanding lift off is essential for effectively interpreting the results of Eddy Current tests, especially in applications where the probe may not remain consistently positioned over the specimen. Other terms like fill factor, edge effect, and end effect pertain to different aspects of electromagnetic testing, but they do not specifically define the change in coupling caused by variations in distance between the probe and the test material in the context described.