Evaluation Method for Electromagnetic Induction Testing of Dielectrics Using Impedance Plane Diagrams Drawn Using Ampère-Maxwell Equation and Simple Electrical Circuit Model

Abstract

EIT was found recently that it can also be applied to dielectrics under a high-frequency AC voltage. However, the EIT evaluation method for dielectrics has not been established sufficiently; in particular, there are no example studies of the drawing of impedance plane diagrams, which is widely used as an evaluation method for eddy current testing (ECT). Therefore, we have attempted to draw an impedance plane diagram based on the Ampère-Maxwell equation and a simple electrical circuit, as performed in ECT. First, a theoretical solution for the impedance based on the Ampère-Maxwell equation that considers eddy and displacement currents was derived, and impedance plane diagrams were then drawn. From the impedance plane diagrams obtained, it was shown that the same trends can be drawn for the diagrams for both conductors and dielectrics. Next, an electrical circuit model for EIT was proposed that takes into account both the conductivity and the permittivity. Using this model, impedance plane diagrams for conductors and dielectrics were drawn, and for dielectrics in particular, it was shown that the diagrams can be drawn by considering the conductivity. In addition, similar to the impedance plane diagrams drawn from the electrical circuit model and derived from the Ampère-Maxwell equation, the change behavior in the diagrams clearly differs between the cases where the conductivity and permittivity change and the case where the lift-off changes. This demonstrates the effectiveness of the electrical circuit model in providing a qualitative understanding of the effects of the dielectric conditions and measurement conditions on EIT.