New Methods for Extraction of VHF Electrical Properties of Conductive Coatings

This paper describes two reflection methods to measure highly conductive coatings at VHF frequencies: 1) a resonant method based on eddy-current sensing at HF and VHF frequencies, and 2) a wideband method at VHF and UHF frequencies, based on a shorted transmission line combined with and computational electromagnetic (CEM) simulations to invert surface impedance. In both cases, the methods are able to determine surface impedances with sensitivities of a small fraction of an ohm. Both methods have strengths and weaknesses with respect to ease of calibration, sensitivity, frequency range, and use on non-flat surfaces. This paper describes both approaches and presents measurements on a variety of conducting materials and coatings. The resulting properties are also compared with DC conductivity measurements collected with a four-point probe system. The predicted accuracy for both methods is presented based on simulated data and empirical measurements.