Permanent magnets - Magnetic circuits functioning

Magnetic circuits, assemblies of magnetic materials, are at the heart of electrical energy. Without them, it would have been impossible to envisage the progress we have made in electricity. The mastery of these magnetic circuits was made possible by the mastery of the laws of electromagnetism and the various research projects undertaken on magnetic materials.

Today, the materials used are few in number and are divided into two families: soft materials and hard materials. Soft materials are used to channel the flux created by electrical sources or hard materials, typically permanent magnets.

Today, permanent magnets have become commonplace, found in many everyday appliances (household appliances, computers, fans, etc.) and "invading" fields of application where, until now, it was impossible to replace traditional systems.

Permanent magnets are never used on their own; on the contrary, they are used in conjunction with a circuit made of soft materials to create interaction forces at a distance. The combination of permanent magnets and soft magnetic materials is commonly referred to as a magnetic circuit.

The permanent magnet synchronous machine is a commonly encountered electromechanical actuator using permanent magnets, which is currently enjoying a boom. This actuator is not the only one to feature a permanent-magnet magnetic circuit, as today there are a multitude of applications.

A permanent magnet magnetic circuit requires careful study in order to exploit the permanent magnet correctly and, consequently, obtain optimum performance for the system in which it is integrated. In this dossier, we cover the operating principles of permanent magnets, so that every reader can analyze a permanent magnet magnetic circuit.

In this issue, we take a closer look at :

• the laws of electromagnetism, with a quick reminder of Maxwell's laws;

• operation of magnetic circuits with magnets, in particular the principles of magnet operation (hysteresis cycle, load line, etc.) and the evolution of magnet performance as a function of the environment;

• the operating principle of a permanent magnet ;

• magnetic circuit sizing, with the main aim of reducing costs.