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Encyclopedia > Reluctance

Magnetic reluctance is the resistance of a material to a magnetic field. It is defined as the ratio of magnetomotive force to magnetic flux. The term was coined in May 1888 by Oliver Heaviside. Current flowing through a wire produces a magnetic field (M) around the wire. ... In physics, the magnetomotive force produces magnetic flux. ... Magnetic flux, is a measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. ... 1888 is a leap year starting on Sunday (click on link for calendar). ... Oliver Heaviside (May 18, 1850 â€“ February 3, 1925) was a self-taught English engineer, mathematician and physicist who adapted complex numbers to the study of electrical circuits, developed techniques for applying Laplace transforms to the solution of differential equations, reformulated Maxwells field equations in terms of electric and magnetic...

The definition can be expressed as:

$S=frac{F}{Phi}$

where

S is the reluctance in ampere-turns per weber (a unit that is equivalent to turns per henry)
F is the magnetomotive force in ampere-turns
Φ is the magnetic flux in weber

The reluctance of a uniform magnetic circuit can be calculated as: The ampere (symbol: A) is the SI base unit of electrical current equal to one coulomb per second. ... In physics, the weber (symbol: Wb) is the SI unit of magnetic flux. ... Henry is a male given name. ...

$S = frac{l}{mu_0 mu_r A}$

where

l is the length of the circuit in metres
μ0 is the permeability of free space, equal to $4 pi times 10^{-7}$ henry per metre
μr is the relative magnetic permeability of the material (dimensionless)
A is the cross-sectional area of the circuit in square metres

The inverse of reluctance is called permeance. The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ... This article is in need of attention. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... Permeance is inverse of reluctance. ...

## Applications GA_googleFillSlot("encyclopedia_square");

The variation in the reluctance of a magnetic circuit, in which part of the circuit is moving, is used in measuring instruments called reluctance sensors. One of the major applications is in magnetic pickups for electric guitars. A pickup device acts as a transducer that captures mechanical vibrations (usually from suitably equipped stringed instruments such as the electric guitar, electric bass guitar or violin) and converts them to an electronic signal which can be amplified and recorded. ... An electric guitar is a type of guitar with a solid or semi-solid body that utilizes electronic pickups to convert the vibration of the steel-cored strings into electrical current. ...

Increasing the reluctance of a magnetic circuit enables it to store more energy before core saturation. This effect is used in the flyback transformer. A flyback transformer or line output transformer (LOPT) is a type of transformer used to generate the high voltage needed for driving a cathode ray tube or picture tube. It converts the input voltage, usually mains voltage in the range 120 to 240 volts, to an output voltage in the...

## References

Chambers Science and Technology Dictionary, "permeance".

Results from FactBites:

 reluctance: Definition, Synonyms and Much More from Answers.com (504 words) Magnetic reluctance is the resistance of a material to a magnetic field. Variation of reluctance is the principle behind the variable reluctance generator and the Alexanderson alternator. The variation in the reluctance of a magnetic circuit, in which part of the circuit is moving, is used in measuring instruments called reluctance sensors.
 Control for variable reluctance motors - Patent 4143308 (5094 words) A control for a variable reluctance motor according to claim 1, in which the diodes in the free-wheel branches are each polarized to oppose flow of current through the associated main control switch in the direction of normal energization for the associated winding. A control for a variable reluctance motor, according to claim 6, in which the charge registering device comprises detection transformers for producing at least one charge registering signal, means for creating a window for eliminating parasitic signals, and a bi-stable trigger circuit for registering the direction of a voltage surge. A control for a variable reluctance motor, according to claim 6, in which the variable device for advance preparation for commutation comprises a memory store for registering the duration of the charging of a capacitor in the turn-off circuit, a ramp generator with a variable threshold, and three registers and three subtractors per channel.
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