Method Using Square-Pulse Excitation for High-Impedance Spectroscopy of Anticorrosion Coatings

This paper presents a method of impedance spectroscopy designed for diagnostics of anticorrosion coatings on objects directly in the field. To shorten the time of impedance spectrum estimation (in the range from 1 mHz to 1 MHz) to a few minutes, harmonic signals were used to determine the spectrum above 10 Hz and a square pulse in the low-frequency range. To determine the impedance spectrum, digital signal processing algorithms adequate to the excitation signal were used. In the high-frequency range, discrete Fourier transform was used, but in the low-frequency range, continuous Fourier transformation was used, calculated in eight segments of acquisition which are dependent on pulse duration time. Experimental verification of the method was performed using four-element two-terminal RC network. The structure and component values of the test object represent the typical equivalent circuit of the anticorrosion coating in the early stage of undercoating rusting. The relative error of identification of component values does not exceed 2%-5%, depending on the placement of the component in the structure of the two-terminal network.