A Novel Conductivity Classification Technique for Nonmagnetic Metal Immune to Tilt Variations Using Eddy Current Testing

The widespread promotion of the concept of circular economy has placed higher demands on the sorting and recycling of metals. Eddy current testing as a non-contact, economical and fast response non-destructive testing technology provides a new development direction for the laborious task of classifying non-magnetic metal. The inevitable inclined surfaces in the metal classification process increase the difficulty of classification. In this paper, we present a novel conductivity classification technique for nonmagnetic metal, which uses the method of minimum error of characteristic slope to identify the metal property. The characteristic slope is extracted by fitting the line obtained from the endpoint of the maximum magnitude of mutual inductance trajectory under different tilt angles. The characteristic slope exists due to the consistency of the phase of the magnitude peak endpoints The test results show that the technique performs accurately in classifying five non-magnetic metals, copper, aluminum, zinc, tin, and titanium, within the tilt angle of 16.7°, and the technique still has good classification performance when the tilt angle is extended to 45°. This method benefits to achieve real-time metal classification.