Highly Sensitive and Robust Eddy Current System for Thickness Measurement of Ceramic Coating Using Near-Resonance Inductance

Eddy current (EC) testing demonstrates engineering value for evaluating quality of thermal barrier coatings (TBCs) in aerospace engines and gas turbines, where top ceramic coating (TC) thickness directly determines thermal protection efficiency and component lifespan. Addressing the dual challenges of impedance coupling in multicoating and low sensitivity caused by low conductivity of bond coating (BC) and substrate, this study proposes a method of TC thickness measurement based on high-frequency excitation and near-resonance inductance. A transformer model of EC axial attenuation in TBCs was established, revealing frequency-dependent EC distribution in both BC and substrate. It was demonstrated that increasing the excitation frequency could effectively reduce the interfacial EC density discrepancy, thereby enabling the isolation of TC thickness from coupled impedance. System sensitivity enhancement was achieved through near-resonance impedance amplification, enabled by an equivalent circuit in a targeted frequency band. A mathematical mapping between resonant impedance and TC thickness was established, validating the efficacy of resonant signal enhancement in EC thickness measurement. The experiment of TC thickness measurement demonstrates a tenfold improvement in sensitivity compared to conventional methods, with measurement errors below 4% . This advancement enables precise quality assessment during TBC manufacturing, addressing critical nondestructive evaluation challenges in multicoating systems.