Parametric analysis of an orthogonal eddy current transducer for measuring the thickness of dielectric coatings

Yurii  Khomiak; Mykyta  Noskov

doi:10.15222/TKEA2026.1.76

Yurii Khomiak NTU «Kharkiv Polytechnic Institute», Ukraine https://orcid.org/0000-0001-6998-8393
Mykyta Noskov NTU «Kharkiv Polytechnic Institute», Ukraine https://orcid.org/0009-0002-2299-1418

DOI: https://doi.org/10.15222/TKEA2026.1.76

Keywords: eddy current testing, dielectric coating, thickness measurement, orthogonal transducer, lift-off, signal-to-noise ratio (SNR)

Abstract

This paper investigates the parameters of orthogonal eddy current transducers (ECTs) for measuring dielectric coating thickness on electrically conductive substrates—a critical task for ensuring product durability and material savings in mechanical engineering, aerospace, and energy applications. The study aims to determine how transducer geometry, excitation frequency, and lift-off influence the useful signal amplitude and signal-to-noise ratio (SNR). Experiments were performed using three ECT variants of different sizes on brass, aluminum, and steel substrates. The results show that the signal amplitude changes monotonically with lift-off, exhibiting maximum sensitivity at small gaps. Signal normalization reveals that the calibration curves are practically frequency-independent, enabling a common normalized characteristic for transducers of the same type. SNR analysis indicates a maximum near 800 kHz for small-sized ECTs, whereas larger transducers peak within the 200–400 kHz range. Furthermore, the upper limit of measurable coating thickness is determined by the width of the active zone b, requiring larger transducers for thicker coatings. The practical significance of this work lies in optimizing the frequency and geometric parameters of ECTs to improve measurement accuracy, simplify high-frequency circuitry, and reduce material waste during quality control.

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