Thickness Measurement of Titanium Alloy Sheet Based on Eddy Current Method With a Novel Simplified Model

This article proposes a novel simplified model that describes the real part (in-phase component) of the difference in pickup coil voltage when an eddy current (EC) sensor consisting of two coils (excitation and pickup coils) is placed above the titanium (Ti) alloy sheet. A parameter that encapsulates the coil geometry factors is integrated into the classical Dodd–Deeds model, and then, the model is simplified by combining with the electromagnetic properties of Ti alloy. The use of the simplified model provides a thickness measurement method for Ti alloy sheets. The measured thickness can be calculated directly from the calibration signal by using the model, without the need to predict response by solving the forward model in advance. Experimental measurements were conducted on TC4 (Ti-6Al-4V) Ti alloy sheets of different thicknesses with a developed EC sensor and measurement system. The experiment verified the proposed model and measurement method. The experimental results shown that the maximum measurement error is less than 2.86%, which is greatly lower than the permissible error of the current industry standard. This study provides a theoretical basis and a fast method for EC thickness measurement of Ti alloy.