Electronic – Magnetic equivalent circuit with permanent magnets


I am fighting to understand how permanent magnets are inserted in magnetic equivalent circuits. In the image below is an example, at the left, the physical representation of an Iron core with a permanent magnet and air gap, at the right, the supposedly magnetic equivalent circuit of a permanent magnet.

Now, when I apply the kirchoff voltage law I know I have to get

H_Fe L_Fe + H_g L_g + H_m L_m = 0

but then why doesn't the magnetic reluctance R_m appear in the voltage law? For me, it would be

H_Fe L_Fe + H_g L_g + H_m L_m + R_m FI = 0

why doesn't the last term appear on the voltage law?

Thank you!

Best Answer

Magnetic field strength, H is measured in ampere-turns per metre and to convert these to the equivalent of voltages in an electric circuit you multiply by the path length - OK this produces a quantity with the units of amperes (actually magneto motive force and equivalent to emf in e-circuits) and that might confuse the innocent but, it is strictly correct - why then do you consider bringing relutance into the equation as being relevant. (By the way it isn't).