A Non-destructive Metal Classification System Based on Magnetic Induction and Mutual Impedance Measurement

This paper presents a non-destructive metal classification system, which is based on magnetic induction and mutual impedance measurement technology. The detection system mainly consists of a signal source, a power amplifier, an ADC acquisition module and a dual-coil sensor. In the dual-coil sensor, the primary coil is excited by low-frequency current, and it then produce a changing magnetic field. In the secondary coil, electromotive force is induced. The current and induced electromotive force are measured through ADC acquisition. And then, mutual impedance of the dual-coil sensor can be obtained by signal processing. The metal material, which is placed between the dual-coil sensor, can influence the measured mutual impedance, and this can be utilized in classification. A prototype was manufactured, and the measured and simulated results are also provided to demonstrate the validity of this non-destructive metal classification system. Additionally, for enhancing the robustness of the system, an RNN model is investigated to alleviate the influence of variations in metal material size.