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In the conventional electromagnetic tube expansion, the end effects generated by the conventional helix coil may lead to inhomogeneous tube deformation in the axial direction. This paper is aimed at overcoming this issue by proposing a new concave coil structure to replace the helix coil currently used by the industry practice to generate a radial electromagnetic force on the tube. The proposed concave coil is expected to reinforce the electromagnetic force distribution profile and, hence, improving the axial inhomogeneous deformation of the tube. In this context, a new R-L criterion of deformation uniformity is first proposed. Second, an electromagnetic-structural coupling finite element model is established to investigate the relationship between the distribution of electromagnetic force generated by the concave coil and the uniformity of the tube under various voltage levels. The effectiveness of the proposed method is validated through a series of experimental and simulation analyses. Furthermore, based on the characteristics of the electromagnetic tube expansion, a modified multilayer concave coil structure is proposed to overcome the axial inhomogeneous deformation of long tubes.