Air Gap:
Alow permeability gap in the flux path of a magnetic circuit. Oftenair, but inclusive of other materials such as paint, aluminum,etc.
AnisotropicMagnet:
Amagnet having a preferred direction of magnetic orientation, sothat the magnetic characteristics are optimum in one preferreddirection.
ClosedCircuit:
Thisexists when the flux path external to a permanent magnet isconfined within high permeability materials that compose the magnetcircuit.
CoerciveForce, Hc:
Thedemagnetizing force, measured in Oersteds, necessary to reduceobserved induction, B, to zero after the magnet has previously beenbrought to saturation.
Curie Temperature,Tc:
Thetemperature at which the parallel alignment of elementary magneticmoments completely disappears, and the material is no longer ableto hold magnetization.
DemagnetizationCurve:
Thesecond quadrant of the hysteresis loop, generally describing thebehavior of magnetic characteristics in actual use. Also known asthe B-H Curve.
EddyCurrents:
Circulating electrical currents that are induced inelectrically conductive elements when exposed to changing magneticfields, creating an opposing force to the magnetic flux. Eddycurrents can be harnessed to perform useful work (such as dampingof movement), or may be unwanted consequences of certain designs,which should be accounted for or minimized.
Electromagnet:
Amagnet, consisting of a solenoid with an iron core, which has amagnetic field existing only during the time of current flowthrough the coil.
EnergyProduct:
Indicates the energy that a magnetic material can supply to anexternal magnetic circuit when operating at any point on itsdemagnetization curve. Calculated as Bd x Hd,and measured in Mega Gauss Oersteds, MGOe.
FerromagneticMaterial:
Amaterial whose permeability is very much larger than 1 (from 60 toseveral thousand times 1), and which exhibits hysteresisphenomena.
Flux
The condition existing in a medium subjected to amagnetizing force. This quantity is characterized by the fact thatan electromotive force is induced in a conductor surrounding theflux at any time the flux changes in magnitude. The cgs unit offlux is the Maxwell.
Fluxmeter:
Aninstrument that measures the change of flux linkage with a searchcoil.
FringingFields:
Leakage flux particularly associated with edge effects in amagnetic circuit.
Gauss:
Lines of magnetic flux per square centimeter, cgs unit of fluxdensity, equivalent to lines per square inch in the English system,and Webers per square meter or Tesla in the SI system.
Gaussmeter:
Aninstrument that measures the instantaneous value of magneticinduction, B. Its principle of operation is usually based on one ofthe following: the Hall effect, nuclear magnetic resonance (NMR),or the rotating coil principle.
HysteresisLoop:
Aclosed curve obtained for a material by plotting correspondingvalues of magnetic induction, B, (on the abscissa) againstmagnetizing force, H, (on the ordinate).
Induction,B:
Themagnetic flux per unit area of a section normal to the direction offlux. Measured in Gauss, in the cgs system of units.
Intrinsic Coercive Force,Hci:
Measured in Oersteds in the cgs system, this is a measure ofthe materialيs inherent ability to resist demagnetization. It isthe demagnetization force corresponding to zero intrinsic inductionin the magnetic material after saturation. Practical consequencesof high Hci values are seen in greater temperature stability for agiven class of material, and greater stability in dynamic operatingconditions.
Intrinsic Induction, Bi:
Thecontribution of the magnetic material to the total magneticinduction, B. It is the vector difference between the magneticinduction in the material and the magnetic induction that wouldexist in a vacuum under the same field strength, H. Thisrelationship is expressed as: Bi = B-H.
Irreversible Loss:
Defined as the partial demagnetization of a magnet caused byexternal fields or other factors. These losses are only recoverableby re-magnetization. Magnets can be stabilized to prevent thevariation of performance caused by irreversible losses.
Isotropic Magnet:
Amagnet material whose magnetic properties are the same in anydirection, and which can therefore be magnetized in any directionwithout loss of magnetic characteristics.
Keeper:
Apiece of soft iron that is placed on or between the poles of amagnet, decreasing the reluctance of the air gap and therebyreducing the flux leakage from the magnet.
Knee of the DemagnetizationCurve:
Thepoint at which the B-H curve ceases to be linear. All magnetmaterials, even if their second quadrant curves are straight lineat room temperature, develop a knee at some temperature. Alnico 5exhibits a knee at room temperature. If the operating point of amagnet falls below the knee, small changes in H produce largechanges in B, and the magnet will not be able to recover itsoriginal flux output without re-magnetization.
Leakage Flux:
Thatportion of the magnetic flux that is lost through leakage in themagnetic circuit due to saturation or air-gaps, and is thereforeunable to be used.
Length of air-gap,Lg:
Thelength of the path of the central flux line in the air-gap.
Load Line:
Aline drawn from the origin of the Demagnetization Curve with aslope of -B/H, the intersection of which with the B-H curverepresents the operating point of the magnet. Also see PermeanceCoefficient.
Magnetic Circuit:
Anassembly consisting of some or all of the following: permanentmagnets, ferromagnetic conduction elements, air gaps, electricalcurrents.
Magnetic Flux:
Thetotal magnetic induction over a given area. When the magneticinduction, B, is uniformly distributed over an area A, MagneticFlux = BA.
Magnetizing Force,H:
Themagnetomotive force per unit length at any point in a magneticcircuit. Measured in Oersteds in the cgs system.
Magnetomotive Force, F:
Analogous to voltage in electrical circuits, this is themagnetic potential difference between any two points.
Maximum Energy Product,BHmax:
Thepoint on the Demagnetization Curve where the product of B and H isa maximum and the required volume of magnet material required toproject a given energy into its surroundings is a minimum. Measuredin Mega Gauss Oersteds, MGOe.
NorthPole:
Thatpole of a magnet which, when freely suspended, would point to thenorth magnetic pole of the earth. The definition of polarity can bea confusing issue, and it is often best to clarify by using "northseeking pole" instead of "north pole" in specifications.
Oersted,Oe:
Acgs unit of measure used to describe magnetizing force. The Englishsystem equivalent is Ampere Turns per Inch, and the SI systemيs isAmpere Turns per Meter.
Orientation Direction:
Thedirection in which an anisotropic magnet should be magnetized inorder to achieve optimum magnetic properties. Also known as the"axis", "easy axis", or "angle of inclination".
ParamagneticMaterial:
Amaterial having a permeability slightly greater than 1.
Permeance:
Theinverse of reluctance, analogous to conductance in electricalcircuits.
PermeanceCoefficient,Pc:
Ratio of the magnetic induction, Bd, to its self demagnetizingforce, Hd. Pc = Bd / Hd. This is also known as the "load line","slope of the operating line", or operating point of the magnet,and is useful in estimating the flux output of the magnet invarious conditions. As a first order approximation, Bd / Hd =Lm/Lg, where Lm is the length of the magnet, and Lg is the lengthof an air gap that the magnet is subjected to. Pc is therefore afunction of the geometry of the magnetic circuit.
Pole Pieces:
Ferromagnetic materials placed on magnetic poles used to shapeand alter the effect of lines of flux.
RelativePermeability:
Theratio of permeability of a medium to that of a vacuum. In the cgssystem, the permeability is equal to 1 in a vacuum by definition.The permeability of air is also for all practical purposes equal to1 in the cgs system.
Reluctance, R:
Analogous to resistance in an electrical circuit, reluctance isrelated to the magnetomotive force, F, and the magnetic flux by theequation R = F/(Magnetic Flux), paralleling Ohm's Law where F isthe magnetomotive force (in cgs units).
Remanence, Bd:
Themagnetic induction that remains in a magnetic circuit after theremoval of an applied magnetizing force. If there is an air gap inthe circuit, the remanence will be less than the residualinduction, Br.
Residual Induction,Br:
Thisis the point at which the hysteresis loop crosses the B axis atzero magnetizing force, and represents the maximum flux output fromthe given magnet material. By definition, this point occurs at zeroair gap, and therefore cannot be seen in practical use of magnetmaterials.
Return Path:
Conduction elements in a magnetic circuit which provide a lowreluctance path for the magnetic flux.
Reversible TemperatureCoefficient:
Ameasure of the reversible changes in flux caused by temperaturevariations.
Saturation:
Thecondition under which all elementary magnetic moments have becomeoriented in one direction. A ferromagnetic material is saturatedwhen an increase in the applied magnetizing force produces noincrease in induction. Saturation flux densities for steels are inthe range of 16,000 to 20,000 Gauss.
Search Coil:
Acoil conductor, usually of known area and number of turns that isused with a fluxmeter to measure the change of flux linkage withthe coil.
Stabilization:
Exposure of a magnet to demagnetizing influences expected to beencountered in use in order to prevent irreversible losses duringactual operation. Demagnetizing influences can be caused by high orlow temperatures, or by external magnetic fields.
TemperatureCoefficient:
Afactor, which describes the change in a magnetic property withchange in temperature. Expressed as percent change per unit oftemperature.
Weber:
Thepractical unit of magnetic flux. It is the amount of magnetic fluxwhich, when linked at a uniform rate with a single-turn electriccircuit during an interval of 1 second, will induce in this circuitan electromotive force of 1 volt.