How is the impedance related to the position of the pickup coil during eddy current testing?

In eddy current testing, the impedance of the pickup coil is influenced significantly by the properties of the test material and its specific position relative to the coil. As the coil moves across various regions of the test material, the impedance changes due to several factors such as conductivity, magnetic permeability, and the presence of defects or variations in the material.

When the pickup coil is placed over a conductive material, eddy currents are induced, which in turn create their own magnetic fields that interact with the coil. This interaction is affected by the material's electrical properties, which means that the impedance will vary with different test materials, as each material will have a distinct level of conductivity and permeability. Therefore, the choice indicating that impedance varies with the test material accurately captures the relationship between the position of the pickup coil and the response of the impedance during testing processes.

Understanding this relationship is crucial for technicians since variations in impedance can indicate different characteristics or conditions of the material being tested, including potential defects or variations in thickness.