Ag Area of the air gap,or the cross sectional area of the air gap perpendicular to the flux path, is the average cross sectional area of that portion of the air gap within which the application interaction occurs. Area is measured in sq. cm. in a plane

normal to the central flux line of the air gap.

Am Area of the magnet,is the cross sectional area of the magnet perpendicular to the central flux line, measured in sq. cm. at any point along its length. In design, Am is usually

considered the area at the neutral section of the magnet.

B Magnetic induction,is the magnetic field induced by a field strength, H, at a given point. It is the vector sum, at each point within the substance, of the magnetic field strength and resultant intrinsic induction. Magnetic induction is the flux per

unit area normal to the direction of the magnetic path.

Bd Remanent induction,is any magnetic induction that remains in a magnetic material after removal of an applied saturating magnetic field, Hs. (Bd is the magnetic induction at any point on the demagnetization curve; measured in gauss.)

Bd/Hd Slope of the operating line,is the ratio of the remanent induction, Bd, to a demagnetizing force, Hd. It is also referred to as the permeance coefficient, shear line, load line and unit permeance.

BdHd Energy product,indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at any point on its demagnetization curve; measured in megagauss-oersteds.

(BH)max Maximum energy product,is the maximum product of (BdHd) which can be obtained on the demagnetization curve.

Bi (or J) Intrinsic induction,is the contribution of the magnetic material to the total magnetic induction, B. It is the vector difference between the magnetic induction in the material and the magnetic induction that would exist in a

vacuum under the same field strength, H. This relation is expressed by the equation:

Bi = B –H

where: Bi = intrinsic induction in gauss; B = magnetic induction

in gauss; H = field strength in oersteds.

Bm Recoil induction,is the magnetic induction that remains in a magnetic material after magnetizing and conditioning for final use; measured in gauss.

Bo Magnetic induction,at the point of the maxi-mum energy product (BH)max; measured in gauss.

Br Residual induction (or flux density),is the magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss.

f Reluctance factor,accounts for the apparent magnetic circuit reluctance. This factor is required due to the treatment of Hm and Hg as constants.

F Leakage factor,accounts for flux leakage from the magnetic circuit. It is the ratio between the magnetic flux at the magnet neutral section and the average flux present in the air gap. F = (Bm Am)/(B Ag).

F Magnetomotive force,(magnetic potential difference), is the line integral of the field strength, H, between any two points, p1 and p2.

p2

F = ∫ H dl

p1

F = magnetomotive force in gilberts

H = field strength in oersteds

dl = an element of length between the two points, in centimeters.

H Magnetic field strength,(magnetizing or demagnetizing force), is the measure of the vector magnetic quantity that determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point; measured in oersteds.

Hc Coercive forceof a material, is equal to the de magnetizing force required to reduce residual induction, Br, to zero in a magnetic field after magnetizing to saturation; measured in oersteds.

Hci Intrinsic coercive forceof a material indicates its resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in oersteds.

Hdis that value of H corresponding to the remanent induction, Bd; measured in oersteds.

Hmis that value of H corresponding to the recoil induction, Bm; measured in oersteds.

HOis the magnetic field strength at the point of the maximum energy product (BH)max; measured in oersteds.

Hs Net effective magnetizing force,is the magnetizing force required in the material, to magnetize to saturation measured in oersteds.

ℓg Length of the air gap,is the length of the path of the central flux line of the air gap; measured in centimeters.

ℓm Length of the magnet,is the total length of magnet material traversed in one complete revolution of the center- line of the magnetic circuit; measured in centimeters.

ℓm/D Dimension ratio,is the ratio of the length of a magnet to its diameter, or the diameter of a circle of equivalent crosssectional area. For simple geometries, such as bars and rods, the dimension ratio is related to the slope of the operating line of the magnet, Bd/Ha.

P Permeance,is the reciprocal of the reluctance, R, measured in maxwells per gilbert.

R Reluctance,is somewhat analogous to electrical resistance. It is the quantity that determines the magnetic flux, ¿, resulting from a given magnetomotive force, F.

where: R = F/¿

R = reluctance, in gilberts per maxwell

F = magnetomotive force, in gilberts

¿ = flux, in maxwells

Tc Curie temperature,is the transition temperature above which a material loses its magnet properties.

Tmax Maximum service temperature,is the maximum temperature to which the magnet may be exposed with no significant long range instability or structural changes.

Vg Air gap volume,is the useful volume of air or nonmagnetic material between magnetic poles; measured in cubic centimeters.

μ permeability,is the general term used to express various relationships between magnetic induction, B, and the field strength, H.

μre recoil permeability,is the average slope of the recoil hysteresis loop. Also known as a minor loop.

ø magnetic flux,is a contrived but measurable concept that has evolved in an attempt to describe the “flow” of a magnetic field. Mathematically, it is the surface integral of the normal component of the magnetic induction, B, over an area, A.

ø = ∫ ∫ B • dA

where:

ø = magnetic flux, in maxwells

B = magnetic induction, in gauss

dA = an element of area, in square centimeters

When the magnetic induction, B, is uniformly distributed and

is normal to the area, A, the flux, ø = BA.

A closed circuit conditionexists when the external flux path of a permanent magnet is confined with high permeability material.

The demagnetization curveis the second (or fourth) quadrant of a major hysteresis loop. Points on this curve are designated by the coordinates Bd and Hd.

A fluxmeteris an instrument that measures the change of flux linkage with a search coil.

The gaussis the unit of magnetic induction, B, in the cgs electromagnetic system. One gauss is equal to one maxwell per square centimeter.

A gaussmeteris an instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following: the Halleffect, nuclear magnetic resonance (NMR), or the rotating coil principle.

The gilbertis the unit of magnetomotive force, F, in the cgs electromagnetic system.

A hysteresis loopis a closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction, B, for ordinates and magnetizing force, H, for abscissa when the material is passing through a

complete cycle between definite limits of either magnetizing force, H, or magnetic induction, B.

Irreversible lossesare defined as partial demagnetization of the magnet, caused by exposure to high or low temperatures external fields or other factors. These losses are recoverable by remagnetization. Magnets can be stabilized against irreversible losses by partial demagnetization induced by temperature cycles or by external magnetic fields

A keeperis a piece (or pieces) of soft iron that is placed on or between the pole faces of a permanent magnet to decrease the reluctance of the air gap and thereby reduce the flux leakage from the magnet. It also makes the magnet less susceptible to demagnetizing influences.

Leakage fluxis flux, ø, whose path is outside the useful or intended magnetic circuit: measured in maxwells.

The major hysteresis loopof a material is the closed loop obtained when the material is cycled between positive and negative saturation.

The maxwellis the unit of magnetic flux in the cgs electromagnetic system. One maxwell is one line of magnetic flux.

The neutral sectionof a permanent magnet is defined by a plane passing through the magnet perpendicular to its central flux line at the point of maximum flux.

The oerstedis the unit of magnetic field strength, H, in the cgs electromagnetic system. One oersted equals a magnetomotive force of one gilbert per centimeter of flux path.

An open circuit conditionexists when a magnetized magnet is by itself with no external flux path of high permeability material.

The operating linefor a given permanent magnet circuit is a straight line passing through the origin of the demagnetization curve with a slope of negative Bd/Hd. (Also known as permeance coefficient line.)

The operating pointof a permanent magnet is that point on a demagnetization curve defined by the coordinates (BdHd) or that point within the demagnetization curve defined by the coordinates (BmHm).

An oriented (anisotropic) materialis one that has better magnetic properties in a given direction.

A permeameteris an instrument that can measure, and often record, the magnetic characteristics of a specimen.

Reversible temperature coefficientsare changes in flux which occur with temperature change. These are spontaneously regained when the temperature is returned to its original point.

Magnetic saturationof a material exists when an increase in magnetizing force produces no increase in intrinsic induction.

A search coilis a coiled conductor, usually of known area and number of turns, that is used with a fluxmeter to measure the change of flux linkage with the coil.

The temperature coefficientis a factor which describes the reversible change in a magnetic property with a change in temperature. The magnetic property spontaneously returns when the temperature is cycled to its original point. It usually is expressed as the percentage change per unit of temperature.

An unoriented (isotropic) materialhas equal magnetic properties in all directions.