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Definitions & Glossary of Terms

  

   Item Description
Air Gap A low permeability gap in the flux path of a magnetic circuit. Often air, but inclusive of other materials such as paint, aluminum, etc.
Area of the air gap, Ag 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.
Anisotropic Material that have a "preferred" magnetization direction. These materials are typically manufactured in the influence of strong magnetic fields, and can only be magnetized through the preferred axis.
Area of the magnet, Am The cross sectional area of the magnet perpendicular to the central flux lne, measured in sq. cm. at any point along its length. In design, Am is usually considered the area at neutral section of the magnet.
Br, Magnetic induction 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 the 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 lien, load line and unit permeance.
Bd/Hd 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.
Bg magnetic induction in the air gap Is the average value of magnetic induction over tha area of the air gap, Ag; or it is the magnetic induction measured at a specific point within the air gap; measured in gauss
BH curve See Demagnetization Curve
(BH)max, Maximum energy products is the maximum product of (BdHd) which can be obtained on the demagnetization curve.
Bi or Bj 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.

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, shown in data as "Br".
Closed circuit condition A condition that exists when the external flux path of a permanent magnet is confined with high permeability material.
Coercive Force, Hcb The demagnetizing force, measured in Oersteds, necessary to reduce observed induction, B, to zero after the magnet has previously been brought to saturation.
Demagnetization Curve Is the second (or fourth) quadrant of  a major hysteresis loop. Points on this curve are designated by the coordinates Bd and Hd. This curve is also referred to as the Second Quadrant Curve, BH Curve, or abbreviated to "curve".
Eddy Currents Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. eddy currents can be harnessed to perform useful work (such as damping of movement), or may be unwanted consequences of certain designs which should be accounted for or minimized.
Ferromagnetic material A material whose permeability is very much larger than 1 (from 60 to several thousand times 1), and which exhibits hysteresis phenomena.
Flux, The condition existing in a medium subjected ot magnetizing force. This quantity is characterized by the face that an electromotive force is induced in a conductor surrounding the flux at any time the flux changes in magnitude. The cgs  unit of flux is the maxwell.
Fluxmeter Is an instrument that measures the change of flux linkage with a search coil.
Gauss Unit of magnetic induction, B, in the cgs electromagnetic system. One gauss is equal to one maxwell per square centimeter.
Gaussmeter Is an instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following; the Hall-effect, nuclear magnetic resonance (NMR), or the rotating coil principle.
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 force Of a material, is equal to the demagnetizing force required to reduce residual induction, Br, to zero in a magnetic field after magnetizing to saturation; measured in oersteds.
Hci Intrinsic coercive force Of 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 go saturation; measured in oersteds.
Hd Is that value of H corresponding to the remanent induction, Bd; measured in oersteds.
Hk Coercive force-k The value of Hcj at 0.9Br. This value gives an indication of the "squareness" of the intrinsic curve. The more square the intrinsic curve, the closer the material is to being ideal. Hk values that approach the Hci values are considered extremely good materials.
Hysteresis Loop The 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.
Induction, B The magnetic flux per unit area of a section normal to the direction of flux. Measured in gauss, in the cgs system of units.
Irreversible Losses Partial demagnetization of the magnet, caused by exposure o 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.
Isotropic A magnetic material that has the "same" properties in all directions. Such a material may be magnetized in any direction since it does not have a "preferred" alignment direction.
Knee of the Demagnetization Curve The point at which the B-H curve ceases to be linear. All magnet materials, even if their second quadrant curves are straight line at room temperature, develop a knee at some temperature. Alnico 5 exhibits a knee at room temperature. If the operating point of a magnet falls below the knee, small changes in H produce large changes in B, and the magnet will not be able to recover its original flux output without remagnetization.
Leakage flux that portion of the magnetic flux that is lost through leakage in the magnetic circuit due to saturation or air-gaps, and is therefore unable to be used.
Load line A line drawn from the origin of the Demagnetization curve with a slope of -B/H, the intersection of which with the B-H curve represents the operating point of the magnet. Also see permeance coefficient.
Magnetic flux, The total magnetic induction over a given area. When the magnetic induction, B, is uniformly distributed over an area A, =BA. The general equation is =ҡBҡdA.
Magnetic Saturation Of a material exists when an increase in magnetizing force, H, does not cause an increase in the intrinsic magnetic induction, B, of the material.
Maxwell Unit of magnetic flux in the cgs electromagnetic system. One maxwell is one line of magnetic flux.
North pole That ole of a magnet which, when freely suspended, would point to the north magnetic pole of the earth. The definition of polarity can be a confusing issue, and it is often best to clarify by using "north seeking pole" instead of "north pole" in specifications.
Oersted, Oe 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.
Open circuit condition Exists when a magnetized magnet is by itself with no external flux path of  high permeability material.
Operating Line For a given permanent magnet circuit is a straight line passing through the origin of the demagnetization curve with a slope of negative Bd/H.  (Also known as permeance coefficient line.)
Operating point Of 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).
Orientation direction The direction in which an anisotropic magnet should be magnetized in order to achieve optimum magnetic properties. Also known as the "axis", "easy axis", or "angle of inclination".
Permeance The inverse of reluctance, analogous to conductance in electrical circuits.
Permeance Coefficient, Pc Ratio of the magnetic induction, Bd, to its self demagnetizing force, Hd. Pc=Bd/Hd. this is also known as the "load line" or operating point of the magnet, and is useful in estimating the flux output of the magnet in various conditions. As a first order approximation, Bd/Hd=Lm/Lg, where Lm is the length of the magnet, anad Lg is the length of an air gap that the magnet is subjected to. Pc is there fore a function of the geometry of the magnetic circuit.
µ permeability Is the general term used to express various relationships between magnetic induction, B, and the field strength, H.
µre recoil permeability The average slope of the recoil hysteresis loop. Also known as a minor loop.
Pole pieces Ferromagnetic materials placed on magnetic poles used to shape and alter the effect of lines of flux.
Permeameter Is an instrument that can measure, and often record, the magnetic characteristics of a specimen.
Permeance coefficient line see operating line.
Polarity The characteristic of a particular pole at a particular location of a permanent magnet. Differentiates the North from the South Pole.
Relative Permeability, µr The ratio permeability of a medium to that of vacuum; µr=µ/µo. In the cgs system, µo=1 in a vacuum by definition. The permeability of air is also for all practical purposed equal to 1 in the cgs system.
R Reluctance Is somewhat analogous to electrical resistance. It is the quantity that determines the magnetic flux, reslting from given magnetomotive force, F where: R=F/. R=reluctance, in gilberts er maxwell, F=magnetomotive force, in gilberts, =flux, in maxwell.
recoil induction, Bm The magnetic induction that remains in a magnetic material after magnetizing and conditioning for final use; measured in gauss
Reversible temperature coefficient Are changes in flux, which occur with temperature change. These are spontaneously regained when the temperature is returned to its original point.
Search Coil 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.
Saturation The condition under which all elementary magnetic moments have become oriented in one direction. A ferromagnetic material is saturated when an increase in the applied magnetizing force produces no increase in induction. saturation flux densities for steels are in the range of 16,000 to 20,000 Gauss.
Stabilization Exposure of a magnet to demagnetizing  influences expected to be encountered in use in order to prevent irreversible losses during actual operation. Demagnetizing influences can be caused by high or low temperatures, or by external magnetic fields.
Tc Curie Temperature Is the transition temperature above which a material loses its magnetic properties.
Temperature coefficient of Br 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.
Tw,  Maximum Operating Temperature The maximum operating temperature, also known as maximum service temperature, is the temperature at which the magnet may be exposed to continuously with no significant long-range instability or structural changes. Note that this temperature is a function of the operating point of the magnet, and not an absolute value.
Vg Air gap volume Is the useful volume of air or non-magnetic material between magnetic pole; measured in cubic centimeters.


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