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# Electromagnetic simulation of Duffing lock

Duffing's electromagnetic lock is a kind of electromagnet used to permanent attraction of magnet keeper and it fast releasing when additional coil will be energized.

A holding coil is constantly supplied with properly chosen current that saturates relatively thin iron core in the surroundings of releasing coil. If additional current flows there, a magnetic field will be significantly reduced. If the force of keeper attraction is comparable with the force of the spring, even small demagnetizing current will release the magnet keeper.

Problem type:
Plane parallel nonlinear magnetostatic.

Geometry of the electromagnetic lock:

Depth of electromagnetic lock: 5 cm.

Given:
Core and keeper material: iron
magnetic permeability: nonlinear
Holding coil total (n*I)h = 100'000 A·turns;
Releasing coil total current (n*I)r = 50'000 A·turns;
Force of stretching spring F = 250 N/m

Results:
When releasing coil is not energized (I=0, edlock_1 case) then the force of keeper attraction is about 295 N/m. Otherwise (I>0, edloc_2 case) the attraction force decreases to 225 N and becomes less then stretching force of the spring, and magnet keeper will be unlocked. The force was calculated by means of "Integral calculator" tools.

 Ih, A·turns Ir, A·turns F, N/m 100000 0 295 100000 50000 225