| INDUSTRIAL MAGNETIC DEVICES |
| PERMANENT MAGNETIC MATERIALS |
|
|
|
| MAGNET TERMINOLOGY GLOSSARY |
<1> <2>
Page |
The terms have been compiled to assist you with sharing information, experience, and knowledge.
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.
Anisotropic Magnet:
A magnet having a preferred direction of magnetic orientation,
so that the magnetic characteristics are optimum in one
preferred direction.
Closed Circuit: This
exists when the flux path external to a permanent magnet
is confined within high permeability materials that compose
the magnet circuit.
Coercive Force, Hc:
The demagnetizing force, measured in Oersteds, necessary
to reduce observed induction, B, to Zero after the magnet
has prviously been brought to saturation.
Curie Temperature, Tc:
The temperature at which the parallel alignment of elementary
magnetic moments completely disappears, and the material
is no longer able to hold magnetization.
Demagnetization Curve:
The second quadrant of the hysteresis loop, generally
describing the behavior of magnetic characteristics in
actual use, Also known as the B-H 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
pemeability is very much larger than 1 (from 60 to several
thousand times 1),and which exhibits hysteresis phenomena.
Flux,O:The 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: Lines of magnetic flux per square
centimeter, cgs unit of flux density, equivalent to lines
per square inch in the English system, and webers per
square meter or Tesla in the SI system.
Hysteresis Loop: A closed curve obtained
for a material by plotting corresponding values of magnetic
induction , B , (on the abscissa) against magnetizing
force, H (on the ordinate).
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.
Intrinsic Coercive force, Hci: Measured
in Oersteds in the cgs system, this is a measure of the
material's inherent ability to resist demagnetiza-tion.
It is the demagnetization force correponding to zero intrinsic
induction in the magnetic material after saturation. Practical
consequences of high Hci values are seen in greater temperature
stability for a given class of material, and greater stability
in dynamic operating conditions.
Irreversible Loss: Defined as the partial
demagnetization of a magnet caused by external fields
of other factors. These losses are only recoverable by
remagnetization. Magnets can be stabilized to prevent
the variation of performance caused by irreversible losses.
Isotropic Magnet: A magnet material whose
magnetic properties are the same in any direction, and
which can therefore be magnetized in any direction without
loss of magnetic characteristics.
Keeper: A piece of soft iron that is placed
on or between the poles of a magnet, decreasing the reluctance
of the air gap and thereby reducing the flux leakage from
the magnet.
Knee of the Demagnetization Curve: The
point at which the B-H curve ceases to be linear. All
magnet materials, even if their second quadrantcurves
are straight line at room tempera-ture, develop a knee
at some temperature. Alnico 5 exhibits a knee at room
temperature. If the operat-ing 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 recoverits 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.
Length of Air-Gap,Lg: The Length of the
path of the central flux line inthe air-gap.
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 Coeffcient.
|
|
|
