Measurement of the Thickness and Conductivity of Nonmagnetic Material Using the Phase Feature of the Eddy Current Technique

The conductivity and thickness of metallic materials are crucial parameters for evaluating performance and quality. However, the eddy current (EC) method for measuring conductivity and thickness faces challenges, such as the need for multiple calibrations and complex inversion calculations. In this paper, a new simplified model and measurement method are proposed. First, according to the electromagnetic properties of non-magnetic materials at low and high frequencies, the classical Dodd-Deeds analytical model is simplified and analyzed. This derivation establishes a relationship between the phase feature of the impedance variation of the EC sensor and both conductivity and thickness, while also providing a basis for frequency selection. Additionally, a measurement method based on the simplified model is designed, which enables the simultaneous measurement of both conductivity and thickness in a single test. Finally, experiments verify the effectiveness of the proposed model and measurement method. The experimental results indicate that the relative errors in measuring conductivity and thickness are within 2.57% and 2.8%, respectively. The method directly calculates conductivity and thickness from the measured phase of the coil impedance variation, without the need for calibration or complex inversion processes, making the calculations simple, fast and accurate. These qualities make it ideal for online measurements or the design of portable measuring instruments.