Imaging the solidification of molten metal by eddy currents : I

This paper presents an eddy-current-based technique for imaging the solidification of molten metal inside a metal pipe. This technique is motivated by the fact that the ac (alternating current) impedance seen from a solenoid placed outside the pipe is dependent on the distribution of the solidification inside the pipe provided that the ac frequency is properly chosen and the overall thickness of the pipe and solidification is small. This paper first establishes a simplified mathematical model based on the fundamental electromagnetic theory, which reveals the exact relationship between the solidification inside the pipe and the scattered field outside the pipe. Based on this model, an iterative algorithm for reconstructing the solidification distribution is then developed. (Some figures in this article appear in colour in the electronic version; see www.iop.org)