In systems using encircling coils, coupling efficiency is referred to as what?

In systems that utilize encircling coils, coupling efficiency is specifically referred to as the fill factor. The fill factor represents the ratio of the area of the coil that is filled with the test material to the overall area of the coil. It takes into account how effectively the coil interacts with the material being tested and is crucial for determining the sensitivity and performance of the electromagnetic testing system. A higher fill factor implies better coupling between the coil and the test material, leading to more reliable measurement results.

Lift-off primarily describes the distance between the coil and the surface of the material, affecting the measurement but not directly defining coupling efficiency. Edge effect refers to the phenomenon where the response of a test material is influenced by its physical edges, which does not pertain directly to the coupling efficiency of the coil. Phase differentiation deals more with the analysis of signal phases and is not directly related to the efficiency of coupling in encircling coil systems.