Thickness and Conductivity Measurement of Multilayered Electricity-Conducting Coating by Pulsed Eddy Current Technique: Experimental Investigation

Abstract

Electricity-conducting coatings are widely applied in industries, such as thermal barrier coating in the aerospace field. Therefore, it is necessary to detect the thickness and the conductivity of the coatings to ensure the quality of the coating. Extended on the existing work on the coating and conductivity detection by the traditional eddy current (EC) technique, this paper investigates the feasibility of the pulsed EC (PEC) technique in coating conductivity and thickness detection. For the single-layered electricity-conducting coating, the coupled influence of the coating conductivity on the relationship between the coating thickness and the PEC detection signal is deeply analyzed, and the approach to detect the coating thickness and conductivity for single conductivity coating is proposed; for the multiple-layered coating, the coupled influence of the coating thickness on the relationship between the other coating thickness and the PEC detection signal is analyzed, and the approach to detect the two-layered electricity-conducting coating thickness is proposed. Finally, a decoupling inversely detection method is proposed to obtain the coating thickness and conductivity, which overcome the singularity of the equation solving method. The results show that the average relative errors of the inverse detection are within 7%. Therefore, the PEC technique can be readily applied to detect the thickness and conductivity of the multiple-layered electricity-conducting coating in spacecraft, pipeline, and high-speed cutting tools.