A Novel Conductivity Classification Technique for Non-Magnetic Tilting Metals by Eddy Current Sensors

The classification of conductivity is significant for recycling metallic scraps. The eddy current sensor is distinct from other classification methods by its merits of non-contact, economical set-up, fast measuring, and so forth. By introducing a set-up that could ensure the single-valued mutual inductance trajectory on the complex plane, we propose the circle fitting method to extract the global features of different trajectories. It is subsequently observed that the fitting circle centers-one of the global features-for the same conductivity with various tilting angles are distributed longitudinally close to each other. The feature line, which is parallel to the abscissa axis, is introduced to represent this gathering distribution behavior. The feature lines for different conductivity are distinguishable. Thus, we construct a simple classification method with only two steps. The test results show great fidelity of the proposed classification technique which can successfully classify the tilting metallic samples within 11.3°.