Magnetic reluctance

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Magnetic reluctance can be thought of a having an analogous function to resistance in an electrical circuit except that it cannot consume energy.

It is equal to the ratio of the MMF in a passive magnetic circuit and the magnetic flux in this circuit or to the ratio of their amplitude values for a sinusoidal MMF and magnetic flux. It is a scalar value.

[edit] Explanation

If there is no energy loss in a magnetic circuit, then existence of magnetic reluctance (resistance to magnetic flux) does not consume energy, though the relationship is similar to Ohms law for an electric circuit. So for a uniform path of a magnetic circuit the magnetic reluctance <math>z_\mu</math> is determined by the expression:

<math>z_\mu = \frac{1}{\mu_r\mu_0}\frac{l}{S}</math>

where <math>l</math> , <math>S</math> is the length and cross-section of the part of a magnetic circuit;

<math>\mu_r \mu_0</math> is the magnetic permeability.

The term “reluctance” for a magnetic resistance to a magnetic flux was proposed by O. Heaviside. [1]Idea about an application to a magnetic flux the law, which is similar to Ohm's law for a closed electric circuit, is attributed to H. Rowland [2].

[edit] Terminology

The notion of “magnetic resistance” was first mentioned by James Joule [3] and the term "magnetomotive force” was first named by Bosanquet [4].

[edit] Units

Magnetic reluctance [1-4] is measured in units – [1/H] and determined by the formula:

<math>z_\mu = \frac{H}{\Phi} = \frac{H_m}{\Phi_m}</math>

[edit] Applications

• Reluctance motors
• Variable reluctance (magnetic) pickups

[edit] References

1. Heaviside O., Electrical Papers. Vol.2. – L.; N.Y.: Macmillan, 1892, p. 166.
2. Rowland H., Phil. Mag. (4), vol. 46, 1873, p. 140.
3. Joule J., Scientific Papers, vol. 1. – 1884, p. 36.
4. Bosanquet, Phil. Mag., vol. 15, 1883, p. 205.

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