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THE FORCE OF ATTRACTION

Where comes from the force of attraction between 2 magnets and some tracks to follow to optimize your application.

The force of attraction between 2 magnets depends, in a simple way, on 3 elements: the permeability of the air gap, the section of the air gap and the induction. Let's take these 3 terms in order.

1. Permeability

If the permeability of the air gap are air or the wood, then this factor will have no influence in your application.

2. Section

The force of attraction between 2 magnets (all other parameters remain identical) is directly proportional to the cross-section of the air gap.

If you have a magnet who has 5 mm long, 5 mm wide and 5 mm high, it will have a certain strength. If you use a 10 mm long magnet, and the other dimensions remain unchanged, the strength will almost double. We say "almost" because for small dimensions the effect of the extremities may not be totally negligible... only by using finite element calculations can give an exact result. In a simplified way, the force is proportional to the length of the magnet (in the case of do not change the other dimensions or the grade of the magnet).

3. Induction in the air gap

The force of attraction will vary with the square of the induction and it is therefore a very important factor. The induction itself depends on the grade of the magnet (N35 à N55), the thickness of the magnet and the distance between the magnets. If the distance is given, it is therefore an invariant for us. On the other hand, by increasing the thickness of the magnet, we increase the induction for a given air gap. Doubling the thickness of the magnet will not double the induction, but will increase it by a certain factor. This factor is difficult to calculate and requires a finite element simulation.