BASICS ON MAGNETICS

Engineering Fundamentals

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INTRODUCTION

Magnetism is a physical phenomenon on which many applications rely. It is the basis of not only electric motors and actuators, but also plays an important role in electrical circuits.

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Magnetic Field

The magnetic field B describes the total magnetic field within a material. It is a function of the materials permeability, which is analog to a material’s conductivity for electrical circuits. A magnetic field can be produced by either “free” currents or “bound” currents denoted by H and M, respectively. “Bound” currents implies that the electrons are bound to their corresponding atoms but orbit in the same direction, producing microscopic currents, as it occurs in permanent magnets (PM). Similarly to current in electrical circuits, the magnetic field always forms a closed loop path and cannot dissipate.

Hopkinson’s Law

The reluctance is the magnetic analog to resistance in electrical circuits. The only difference is that a resistance dissipates energy, while reluctance stores it. The magnetomotive force (MMF), Reluctance and the Flux relate through Hopkinson’s law:

F=R\Phi

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Magnetic Circuit

Similarly to electrical circuits, a magnetic circuit can be created with Reluctances Flux and MMF sources. The following figures illustrate a setup with a PM, a coil and a Load Reluctance and its corresponding magnetic circuit. A PM can be modelled as a constant flux source with parallel internal reluctance. The coil is modelled as a constant MMF source. Applying Kirchhoff’s circuit laws, all quantities in the magnetic circuit can be solved.

Basics on magnetics

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