In Eddy Current Testing, what does an increased signal strength generally indicate?

In Eddy Current Testing (ECT), an increased signal strength typically indicates a possible surface or near-surface defect. The underlying principle of ECT is that when an alternating current flows through a coil, it generates a magnetic field that induces eddy currents in the conductive material being tested. If there are defects such as cracks, pits, or other imperfections near the surface, these can disrupt the flow of the eddy currents, causing changes in the measured signal’s amplitude or phase.

When the signal strength increases, it typically suggests that the eddy currents are flowing more freely without significant disruptions. This can often mean that the test is detecting features or conditions that are indicative of a shallow defect. Consequently, a stronger signal may be associated with the presence of surface or near-surface defects that affect the electromagnetic field's distribution, leading to notable variations in the signal received by the testing equipment.

While other options describe conditions that could be observed in ECT, they do not align with the interpretation of increased signal strength in the way that surface defects do. For instance, minor defects may not necessarily produce a strong signal change, excessively heated materials could lead to other response issues unrelated to signal strength, and non-conductive materials would not generate eddy currents at