Figure 2. two coaxial coils. It is assuming that axes of coils and z axes are matched. z1, z2, z3 and z4 are the top and bottom of the coils

From

Simulation of Magnetic Force between Two Coaxial Coils with Air Core and Uniform Flow in MATLAB

Ali Jebelli, Arezoo Mahabadi, Hicham Chaoui, Mustapha C. E. Yagoub

International Journal of Physics. 2021, 9(4), 186-196 doi:10.12691/ijp-9-4-1