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GLOSSARY OF MAGNETIC TERMINOLOGY
Anisotropic-They are magnets that have an easy axis of magnetization, so that the magnetic characteristics are optimal in one direction.
Air Gap-the air or nonmagnetic material between magnetic poles.
B (Magnetic Induction)-is the magnetic flux per unit area normal to the direction of the magnetic path. It is measured in Gauss, in the cgs system of units.
Bd (Remnant Induction)-magnetic induction that remains in a magnetic material after removal of an applied magnetic force.
BHmax (Maximum Energy Product)-the point on the demagnetization curve where the values of B & H are maximized. Measured in MGOe.
Bi (Intrinsic Induction)-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: Bi=B-H
Br (Residual induction)-also the flux density, it represents the maximum flux output from the given magnetic material.
Closed Circuit-exists when the external flux path of a permanent magnet is confined with high permeability materials.
Curie Temperature (Tc)-The temperature at which the magnetic alloy completely loses it's characteristics, and the material is no longer able to hold magnetization.
Demagnetization Curve-Also known as the BH Curve, it is the second/fourth quadrant of a hysteresis loop.
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 dampening of movement), or may be unwanted consequences of certain designs, which should be accounted for of minimized.
F (Magneto Motive Force)-the magnetic potential difference between any two points.
Ferromagnetic Material-material whose permeability is very much larger than 1 (from 60 to several thousands times 1), and which exhibits hysteresis phenomena.
Flux-condition existing in a medium subjected to a magnetizing force. This quantity is characterized by the fact 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.
Fringing Fields-leakage flux particularly associated with edge effects in a magnetic circuit.
Gauss-unit of magnetic induction (B), in the cgs unit of flux density. One gauss is equal to one maxwell per square centimeter, equivalent to lines per square inch, and Webers per square meter or Tesla.
Gauss Meter-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 Force)-is the magnetizing/demagnetizing force per unit length at any point in a magnetic circuit. Measured in Oersteds.
Hc (Coercive Force)-is the demagnetizing force needed to reduce residual induction, B to zero, after magnetizing to saturation. Measured in oersteds.
Hci (Intrinsic Coercive Force)-measurement (in Oersteds) of its resistance to demagnetization. It is the demagnetizing force related in the material to zero after magnetizing to saturation.
Hysteresis Loop-is a closed curve obtained for a material by plotting corresponding values of magnetic induction(B), and magnetizing force(H), for ordinates & abscissa.
Irreversible Loss-a partial demagnetization of the magnet, caused by exposure to external fields(such as high/low temperatures), or other factors. These losses are recoverable by remagnetization, & they can be stabilized by partial demagnetization induced by temperature cycles or by external magnetic fields.
Isotropic-magnetic material with magnetic properties that are the same in any direction, resulting in the ability to be magnetized in any direction.
Keeper-is a piece(s)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. They are usually installed to resist demagnetization for Alnico magnets/assemblies.
Knee of the Demagnetization Curve-the point at which the BH 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 re-magnetization.
Leakage Factor (F)-the ratio between the magnetic flux at the magnet neutral section and the average flux present in the air gap.
F=(B mA m)/(B, A g).
Leakage Flux-is the flux that is lost/leaked in the intended magnetic circuit.
Length of the Air Gap (Lg)-the length of the path of the central flux line of the air gap.
Load Line-the 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 Circuit-an assembly consisting of some or all of the following: permanent magnets, ferromagnetic conduction elements, air gaps, and electrical currents.
Magnetic Flux(?)-the magnetic induction(B) over an area(A), when it is uniformly distributed and is normal to the area.
Magnetic Flux, or ? = BA.
Magnetic Length, The physical length of the magnet dimension which corresponds to the direction the magnet is magnetized. This may or may not be the magnet's orientation direction.
Maxwell-the unit of magnetic flux in the cgs electromagnetic system.
North Pole-the pole 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 the best to clarify by using "north seeking pole" instead of "north pole" in specifications.
Oersted (Oe)-the unit of magnetic force, H, in the cgs electromagnetic system. One oersted (Oe) equals a magneto motive force (F) of one gilbert per cm of flux path.
Open Circuit Condition-when a magnetized magnet is by itself with no external flux path of high permeability material.
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."
Paramagnetic Material-material having a permeability slightly greater than 1.
Permeance(P)-the inverse of reluctance (R).
Permeability (μ )-term used to express vast relationships between magnetic induction (B), and the field strength (H).
Pole Pieces-ferromagnetic materials placed on magnetic poles used to shape and alter the effect of lines of flux.
Reluctance (R)-analogous to electrical resistance in a circuit. It is the quantity that determines the magnetic flux (?), resulting from a given magneto motive force (F). The relation as below:
R=F/?
R=reluctance
F=magneto motive force
?=magnetic flux
Return Path-conduction elements in a magnetic circuit, which provide a low reluctance path for the magnetic flux.
Reversible Temperature Coefficient-The changes in flux caused by tempersture changes that is reversible.
Saturation-The condition where the increase in the magnetic force yields no increase in induction, & all of the elementary magnetic moments are oriented in one direction.
Search Coil-a coiled conductor, usually of known area and number of turns, that is used with a flux meter to measure the change of flux linkage with the coil.
Sintered Magnets-this magnet is produced from a compacted powder, which is then subjected to a heat operation where the full density and magnetic orientation is achieved.
Stabilization-is the 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.
Temperature Coefficients-is a factor which describes the reversible change in a magnetic property with a change in temperature. When the temperature returns to its original point, the magnetic properties return spontaneously. It usually is expressed as the percentage change per unit of temperature.
Weber-the practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric current during an interval of 1 second, will induce in this circuit an electromotive of force of 1 volt.
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