inductance for Loop..
                   R
                 ------->
             _________
            /         \
           /           \
          /             \
         |               \
         |               |
         |               |
          \             /
           \           /
            \_________/


   L_H = Num^2*R_m*ur*uo*(ln(8*R_m/a_m)-2.0)
   mu_0 = 4*pi*1E-7_H/m