The term 'fill factor' is associated with which type of coil?

The term 'fill factor' primarily refers to encircling coils used in Eddy Current Testing. The fill factor is a measure of how well the coil occupies the space within the test object, which is crucial for ensuring that the maximum amount of eddy currents can be induced in the material being tested. An encircling coil surrounds the test specimen, and a higher fill factor indicates that a larger volume of the specimen is being tested, enhancing the coil's sensitivity and efficiency in detecting flaws.

Surface coils and coaxial cables may involve different design considerations and parameters that do not directly relate to the fill factor in the context of eddy current testing. Therefore, while those may be relevant in other applications, they do not apply to the concept of fill factor in the same way encircling coils do. Thus, focusing on encircling coils provides a clear understanding of how coil design impacts the effectiveness of the testing procedure.