A Novel Dual-Mode Sensor for the Detection of Interface Flaw in “Insulator-Conductor” Composite Structures

“Insulator-conductor” composite structures have been extensively used in a vast number of fields in recent years. However, due to different factors including but not limited to environmental and adverse working conditions, the interface between the insulator and conductor is prone to flaws. Therefore, non-destructive testing (NDT) techniques are needed to inspect the functionality and integrity of such composite structures. A dual-mode sensor that combines principles of eddy current and capacitive sensing is proposed to detect the interfacial flaws in “insulator-conductor” composite structures. The proposed sensor uses phase switching excitation to switch between inductive and capacitive detection modes, and the feasibility of the method was analyzed by equivalent circuit analysis and Finite Element (FE) simulations. The dual-mode sensor was fabricated on a single Printed Circuit Board (PCB) and used for experimental investigation on specimens of “Perspex-aluminum” composite structures. The experimental results verified the results of equivalent circuit analysis and FE simulation, and showed that the proposed sensor is able to detect corrosion under insulation, surface cracking on the conductor and interface debonding. Results also show that the detected information of the two modes complement each other, proving that the detection method has the ability to evaluate flaws in complex situations at the interface.