In eddy current testing using the ellipse method, what variable may be indicated by the size of the ellipse opening?

In eddy current testing, the ellipse method visualizes the relationship between the magnitude and phase of the eddy current signals. The size of the ellipse opening is significant because it directly represents the impedance changes in the test material.

A larger ellipse indicates that there are greater variations in the eddy current flow, which may be caused by factors such as defects, changes in material properties, or variations in thickness. Conversely, a smaller ellipse opening usually suggests that the material properties are more uniform, which is characteristic of undamaged or consistent materials.

This relationship highlights the importance of the size of the ellipse opening as a key indicator of the condition of the material being tested. Therefore, the correct option reflects the crucial role that the ellipse's size plays in assessing material integrity through eddy current testing.