A Dual Mode Nondestructive Evaluation Sensor With Simultaneous Inductive and Capacitive Outputs

Abstract

Conventional electromagnetic Non-Destructive Evaluation (NDE) techniques are usually sensitive to either conductors or insulators. The emerging non-destructive assessment of "insulator-conductor" composite structures is thus faced with cost and efficiency problems due to this limitation. In this paper, a novel detection technique that combines inductive and capacitive methods is proposed for the inspection of "insulator-conductor" composite structures. A new structure of a planar inductive-capacitive dual-mode sensor in which the inductive and capacitive modes can be excited simultaneously with a single excitation signal without the need for mode switching is developed. The output signal of this sensor is analyzed in relation to the spatial electromagnetic field using equivalent circuit analysis and finite element (FE) simulation. A signal conditioning module for the proposed sensor is designed and a dual-mode test system that simultaneously detects signals from both modes is built. Experimental results from the test system show that the proposed detection method is sensitive to defects in both the insulating and conducting layers of the "insulator-conductor" composite structure and thus can detect corrosion under the insulation, surface cracks on the conductor and interface debonding with the detected signals able to reflect the size of the defects. The detection information of the two modes is complementary, proving that the method is able to comprehensively evaluate "insulator-conductor" composite structures.