What is the relationship between the dimension and shape of a magnet’s keeper and the shape and strength of the field?
As an example, for a “U” magnet lying on a table, the keeper should be as “deep” as the magnet depth (toward the table) and the keeper thickness should be about 2/3 of the magnet pole width. This is based on the fact that the Br value of the best magnet materials is about 2/3 of the Bs of the best steel. For lower grades of material (lower Br) the keeper thickness should be (Br / 18000) x Wp (magnet pole width). For Alnico 2 this would be 7500 / 18000 x Wp, or 0.42″ for a Wp of 1.0″.
