Magnetic Field Simulator beta

The origin is at the centre of the magnet and positive Y points towards the north pole. The point is marked in the drawing.

Read the values on the surface of the magnet itself with care. On the pole face B is continuous and the value holds on both sides. On the side face B jumps by μ₀M — the value is given both outside and inside. On an edge the field of a perfectly sharp body grows beyond all bounds, so no number is printed there at all.

Magnetisation direction. A block can be magnetised along its height or along its length — the body keeps the same orientation in the drawing, only the faces the poles sit on change. A disc and a ring have one option only, axial, that is along the height.

Field lines inside the magnet as well. Inside the body it is B that is followed, not H — which is why the field line runs there from the south pole to the north pole and the loop closes.

Map inside the magnet as well. Inside the body B = μ₀(H + M), and how much that is depends on the shape. A slender magnet reaches about half of Br at the pole face and nearly the whole of Br at its centre (a 20 × 20 × 60 mm block: 0.49 and 0.94 Br). A flat one reaches far less — a 20 × 20 × 3 mm block holds barely a tenth of Br inside.

Colour bands. The ladder is fixed and the same for every magnet, so two products can be compared at a glance. The steps are uneven, fine at the bottom and coarse at the top, so that ferrite gets ten bands as well. The ceiling is 750 mT — everything above it shares one colour, so the picture does not show how much stronger the field is in the hottest places.

On the surface of the magnet. On a pole face B is continuous and the value holds on both sides. On a side face B jumps by μ₀M. On an edge the field of a perfectly sharp body grows beyond all bounds, so no number exists there — the hottest colours exactly at the corners are a property of the idealised geometry.