Driven by global green and low-carbon development goals, the industry of scrap metal recycling is entering a critical period for robust growth. Compared with other sorting technologies, eddy current testing (ECT) has garnered significant attention due to its advantages of high speed, non-contact operation and low cost. However, current research primarily focuses on non-magnetic metals with pronounced conductivity differences, and considerable improvements are still needed in terms of classification accuracy and detection range. To address this problem, this paper proposes a non-magnetic metal classification method using a dual-excitation array sensor. By superimposing two excitation signals, the method enhances the sensitivity of sensors and achieves metal classification through variations in the phase value of the receiving coil. This work systematically investigates the classification performance of conventional dual-coil sensors and array sensors for metals with different conductivity differences, as well as the detection range of sensors at varying lift-off heights. Experimental results demonstrate that the proposed method effectively differentiates aluminium alloys with subtle conductivity differences, significantly expanding the effective detection range compared to dual-coil sensors. Moreover, within the effective detection range, the classification accuracy for aluminium alloys reaches 97.2%.
Zhang et al. (Sun,) studied this question.