A novel two electrode surface impedance sensor

Although electrochemical impedance spectroscopy (EIS) has been successfully used in the study of coating degradation and corrosion, its application has mainly been limited to laboratory tests. In this study, a two cell EIS (TCEIS) configuration is proposed by introducing a second cell into the traditional single cell EIS (SCEIS) as a substitute of the working electrode, which in the case of SCEIS is usually an electrical connection to the substrate. Compared to the SCEIS, the TCEIS has the following advantages: 1) the substrate connection required by SCEIS can be eliminated; 2) measurement on nonconductive substrate can be made; 3) defects which are not directly underneath the cell could potentially be detected and located. At the current stage, comparison measurements were carried out between SCEIS and TCEIS on coated panels subjected to ultraviolet (UV), salt spray, and alternating UV/salt spray. Finite element analysis (FEA) was used to simulate the EIS measurements for defects with different sizes and different positions present in the coating system to understand the potential uses and limitation of the TCEIS configuration.