Measurement of permeability and radius for asymmetric cylinders with double coils using a simplified analytical model of eddy current testing

This paper proposes a simple and efficient calculation method for evaluating a cylinder and pipe eccentrically placed in a coil pair. By introducing different equivalent radii, an approximate analytical model is established by adapting the Dodd and Deeds(DD) model. Numerical simulations using the finite element method (FEM) are conducted to verify the accuracy and reliability of the proposed simplified analytical model, showing a high level of consistency for both inner and outer double coils. Additionally, experiments are carried out, and the experimental results closely matched the calculated values, with the maximum average error rate being only 0.86%, requiring no more than average 0.061 s to obtain results.

This model not only provides a fast approach for calculating the response of asymmetric cylinders and tubes in eddy current testing (ECT), but also demonstrates excellent accuracy. An estimation method for cylinder radius, conductivity, and permeability under varying levels of eccentricity is also proposed. Experimental validation demonstrates that the estimation error remains below 5%, even in the presence of eccentricity. The method has potential for testing of cylinder or tube in industrial applications using ECT where eccentricity is usually encountered.