Study of permanent-magnet couplings with progressive magnetization using an analytical formulation

Nonclassical structures of permanent-magnet cylindrical air-gap couplings with progressive magnetization are studied. In these couplings, parallelepiped magnets with nonclassical magnetization direction are used and stuck in ironless cores. The magnetization direction of each magnet is chosen to provide an optimal repartition of the induction in the air gap. This progressive magnetization allows very high values of pullout torque. The use of this type of structure with ironless cores and very high pull-out torque seems to be an advantageous way to minimize the inertia and maximize the pullout torque of a magnetic coupling. An efficient method to calculate the torque of such a coupling is presented, based on analytical formulas for forces between magnets. It allows the exact evaluation of the performance of the studied couplings when the main dimensions of the coupling are varying with small calculation time. In this paper the influence of the number of pole pairs, the influence of the number of magnets per pole, the influence of the magnets' thickness, the influence of the air-gap radius, and the influence of the length of the structure are studied and discussed. Then some general rules are presented for efficient design of such a coupling.