What do the limit frequency equations and impedance diagrams for long solid rods and long thin-walled tubing show?

The limit frequency equations and impedance diagrams for long solid rods and long thin-walled tubing are indeed different due to the distinct physical and electromagnetic characteristics of these geometries. In Eddy Current Testing, the interaction between the eddy currents induced in a conductor and the material's shape and permeability plays a crucial role in determining the response of the system.

For long solid rods, the eddy currents are typically distributed throughout the entire volume of the material, which influences the depth of penetration and the way the impedance responds to variations in frequency. In contrast, long thin-walled tubing presents a different scenario, where the eddy currents primarily flow in the wall of the tube. This discrepancy in how eddy currents behave causes variations in the limit frequency equations, which define the range of frequencies that can be effectively used for testing each type of geometry.

Moreover, the impedance diagrams for these structures will demonstrate different characteristics reflecting the distinct ways that the eddy currents are induced and interact with defects or material properties. Therefore, choosing the option that depicts these differences is pivotal in understanding the application and effectiveness of Eddy Current Testing techniques for various material forms.