__Magnetic Terms And
Definitions__

**Magnetic Terms And
Definitions**

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

**Air
Gap: **The portion of a magnetic circuit which contains
no ferrous or magnetic material; this is the portion of the
magnetic circuit where the desired magnetic action will
occur.

**Air Gap Length - lg:**
The length of the path of the central flux line of the air
gap; measured in centimeters.

**Air Gap Volume - Vg: **The
useful volume of air or non-magnetic material between
magnetic poles; measured in cubic centimeters.

**Air Gap Area - Ag: **The
cross-sectional area of the air gap perpendicular to the flux path is measured in square centimeters in a
place normal to the central flux line.

**Ampere-Turn/Meter -
A/m: **The SI unit of magnetizing force or magnetic field
strength.

**Anisotropic Material:**
A material having a preferred magnetization axis. This
characteristic is produced during manufacture by crystalline
structure orientation and/or magnetic field enhancement. Also
referred to as "oriented material".

**Closed
Circuit:** A condition that exists when the external
flux path of a permanent magnet is confined with material
having high permeability.

**Coercive Force - Hc: **The
demagnetizing force required to reduce residual induction
(Br) to zero in a magnetic field after magnetizing to
saturation; measured in oersteds.

**Coercivity: **The
property of magnetic material, which is a function of the
maximum value of its coercive force. A high coercivity
material is one, which exhibits a high coercive force.

**Core Loss: **The
power expended (as heat) in a magnetic or ferrous material
when it is subjected to a varying magnetizing force.
Expressed in watts/pound of material.

**Curie Temperature -
Tc: **The transition temperature above which a material
loses its magnetic properties.

**Demagnetization: **The partial
or complete removal of residual magnetism from a body.

**Demagnetization Curve:
**The second or fourth quadrants of a major hysteresis
loop. The coordinates Bd and Hd designate points on this
curve.

**Diamagnetic Material:**
A material having permeability less than that of a vacuum.

**Dimension Ratio -
lm/D: **The ratio of the length of a magnet to its
diameter, or the diameter of a circle of equivalent
cross-sectional area. For simple geometrics such as bars and
rods, the dimensional ratio is related to the slope of the
operating line of the magnets (Bd/Hd).

**Eddy Current Loss:** The
portion of the core loss in a material due to circulating
currents resulting from emf induced by varying magnetic
induction. A highly conductive material will sustain stronger
eddy currents for a relatively long time, whereas the eddy
currents in poor electrical conductors are weaker and tend to
decay rapidly, if existant at all.

**Electromagnet: **A
temporary magnet, typically formed from a coil of wire wound
around a core made from a soft magnetic material (such as
iron). An electromagnet will only produce a magnet field when
current is passed through the coil.

**Energy Product - BdHd:
**The amount of 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.

**Energy Product Curve: **The
graphic representation of the external energy produced by a
permanent magnet. It is a function of the flux density and
the demagnetizing force shown in the demagnetization curve
(BdHd) plotted against the induction Bd.

**Ferromagnetic Material:**
A material which exhibits hysteresis phenomena and whose
permeability is dependent upon an applied magnetizing force.

**Fluxmeter: **An
instrument that uses a search coil to measure flux linkage
changes.

**Gamma:
**The CGS units of low-level flux density; 100,000 gamma
equals one oersted.

**Gauss: **The CGS
unit of magnetic induction and flux density. One gauss equals
one maxwell per square centimeter.

**Gaussmeter: **An
instrument that measures the instantaneous value of magnetic
induction (B). Guassmeters usually use either the Hall
effect, nuclear magnetic resonance (NMR), or the rotating
coil principle for operation.

**Gilbert: **The CGS
of magnetomotive force. One gilbert equals the amount of
force required to produce one maxwell of flux in a magnetic
circuit having unity reluctance.

**Hard Magnetic Materials: **Materials,
which tend to resist demagnetization once they are
magnetized. All permanent magnet material is considered
"hard". Also referred to as "high
energy-product" materials.

**Hysteresis Loop: **The
graphic representation of the relation between values of
magnetic induction (B) and magnetizing force (H) for a
ferrous or magnetic material. Often referred to as a
"B-H" loop.

**Intrinsic Coercive
Force - Hci:** An indication of a material’s
resistance to demagnetization. It is equal to the
demagnetizing force, which reduces a saturated
material’s intrinsic induction (Bi) to zero; measured in
oersteds.

**Intrinsic Induction -
Bi or J: **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
subtracting the value of H from the value of B.

**Irreversible Losses: **Partial
demagnetization of a magnet caused by exposure to high or low
temperatures, external fields, or other factors. These losses
can be recovered by remagnetization. Magnets can be
stabilized against irreversible losses by partial
demagnetization induced by temperature cycles or by external
magnetic fields.

**Isotropic Material: **A
material that has equal magnetic properties in all direction.
Also referred to as "unoriented material".

**Joint Reluctance: **The
resistance to conduction of a magnetic field caused by joints
or discontinuities in a magnetic circuit. In effect, an air
gap, which causes some degradation in the flux density
available in the working gap of the magnetic assembly.

**Keeper:
**One or more magnetic conductors used to close a magnetic
circuit. Generally used to protect permanent magnets of
magnetic assemblies from demagnetizing influences when the
assembly is not being used. It can also serve to minimize
leakage.

**Leakage Factor - F: **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.

**Leakage Flux: **The
part of a magnet field that is outside the useful of intended
magnetic circuit; measured in maxwells.

**Low Energy Product
Material:** Ferromagnetic material having a low energy
product and which is easily demagnetized. Also known as
"soft" magnetic material.

**Magnetic Area - Am: **The
cross-sectional area of the magnet perpendicular to the
central flux line, measured in square centimeters at any
point along its length. For design purposes, this is usually
considered the area at the neutral section of the magnet.

**Magnet Length - lm:**
The total length of magnet material traversed in one complete
revolution of the centerline of the magnet circuit; measured
in centimeters.

**Magnet Treating: **The
act of magnetically reducing the residual induction in a
magnetic assembly in order to achieve a desired flux density
level in its working gap. This also serves to protect the
assembly against external influences of predetermined levels,
which would otherwise tend to reduce the magnet’s
residual induction. (Also see "stabilization")

**Magnetic Domains: **The
molecular-size magnetic dipoles, which determine the magnetic
characteristics of a permanent magnet.

**Magnetic Field
Strength - H:** A measure of the vector magnetic quantity
that determines the ability of an electric current or
magnetic body to induce a magnetic field at a given point;
measured in oersteds.

**Magnetic Flux - ø:
The** physical indication of a magnetic condition existing
in a material or medium which is subject to a magnetizing
influence. It may be likened to the current flow in an
electrical circuit. The CGS unit for magnetic flux is the
maxwell (M); the SI unit is the weber (Wb).

**Magnetic Induction -
B: **The magnetic field induced in a magnet or ferrous
material by a magnetizing force, H. The CGS unit for magnetic
induction is the gauss; the SI unit is the telsa. The
phenomenon of induction is a function of the permeability of
the material and the applied magnetizing force. Magnetic
induction is the vector sum (at each point within the
material) of the magnetic field strength and the resultant
intrinsic induction, and is expressed as the amount of flux
per unit area normal to the direction of the magnet path.
Also referred to as "magnetic flux density".

**Magnetic Induction In
The Air Gap - Bg**: The average magnetic induction value
over the area of the air gap, of the magnetic induction
measured at a specific point within the air gap; measured in
gauss.

**Magnetic Saturation:**
A condition that exists when an increase in magnetizing force
(H) does not cause an increase in intrinsic magnetic
induction (B). When this condition exists, the magnet is
fully charged.

**Magnetomotive Force -
F: **The line integral of the field strength (H) between
any two points. This is the force, which tends to produce a
magnetic field, expressed in gilberts in the CGS system and
in ampere-turns in the SI.

**Major Hysteresis Loop:**
The closed loop obtained when a magnetic material is cycled
between positive and negative saturation.

**Maximum Energy Product
- (BH) max: **The maximum product of (BdHd) which can be
obtained on the demagnetization curve.

**Maximum Field Strength
- Ho: **The amount of magnetic field strength corresponding
to the maximum energy product (BH) max; measured in oersteds.

**Maximum Magnetic
Induction - Bo: **The magnetic induction at the point of
the maximum energy product (BH)max; measured in gauss.

**Maximum Service
Temperature - Tmax:** The maximum temperature to which a
magnet can be exposed without permanent changes to its
stability or structural integrity.

**Maxwell: **The CGS
unit of magnetic flux. One maxwell equals one line of
magnetic flux.

**Net Effective
Magnetizing Force - Hs: **The magnetizing force
required to saturate a magnetic material; measured in
oersteds.

**Neutral Section: **The
portion of a permanent magnet defined by a plane passing
through the magnet perpendicular to its central line at the
point of maximum flux.

**Oersted:
**The CGS unit of magnetic field strength (H). One oersted
equals a magnetomotive force of one gilbert per centimeter of
flux path.

**Open Circuit:** A
condition that exists when a magnetized object is by itself,
with no external flux path of high-permeability material.

**Operating Line: **A
straight line passing through the origin of a permanent
magnet demagnetization curve, with a slope of negative Bd/Hd;
also called a "permanence coefficient line".

**Operating Point: **The
point on a permanent magnet demagnetization curve defined by
the coordinates Bd and Hd, or the point within the
demagnetization curve defined by the coordinates Bm and Hm.

**Permeability - u: **A general
term used to express various relationship between magnetic
induction (B) and the field strength (H).

**Permeameter:** An
instrument that can measure (and often record) the magnetic
characteristics of a specimen.

**Permeance - P: **The
reciprocal of reluctance (R), measured in maxwells per
gilbert.

**Recoil Force - Hm: **The
amount of magnetic field strength corresponding to the recoil
induction (Bm); measured in oersteds.

**Recoil Induction - Bm:
**The magnetic induction that remains in a magnetic
material after magnetizing and treating for final use;
measured in gauss.

**Reluctance - R: **A
quantity that determines the amount of magnetic flux that is
produced by a given magnetomotive force; it is somewhat
analogous to electrical resistance. The reciprocal of
permeance, it is expressed by the equation R = F/0 and
measured in gilberts-per-maxwell in the CGS systems and
ampere-turns-per-weber in the SI.

**Reluctance Factor - f:
**Accounts for apparent magnetic circuit reluctance.
Required due to the treatment of Hm and Hg as constants.

**Remanence - Bd: **The
magnetic induction remaining in a magnetic circuit after the
removal of an applied saturating magnetic field. If the
circuit incorporates an air gap, the remanence will be less
than the residual induction. Also referred to as
"remanent induction".

**Remanent Force - Hd: **The
amount of magnetic field strength corresponding to the
remanent induction (Bd); measured in oersteds.

**Residual Induction -
Br: **The magnetic induction corresponding to zero
magnetizing force in a magnetic material after saturation in
a closed circuit, measured in gauss. Also referred to as
"flux density".

**Retentivity: **A
material’s ability or inability to retain magnetism
after the magnetizing force is removed.

**Reversible Temperature
Coefficients: **Temporary changes in flux, which occur as
ambient temperature varies. When the ambient temperature
returns to normal, the flux will return to its original
value.

**Saturation Intrinsic
Induction - Bis or Js: **The maximum intrinsic
induction possible in a material.

**Search Coil: **A
coiled conductor used as a sensing element for a fluxmeter.
The coil area and number of turns are usually known; this
information is used to measure flux linkage changes.

**Soft Magnetic
Material:** Ferromagnetic material, which is very easily,
demagnetized; materials having low coercivity, such as relay
steels.

**Stabilization: **The
treatment of a magnetic material in order to obtain a desired
magnetic level and /or to achieve some degree of permanence
of that level. Stabilization may consist of treating the
magnet assembly with and external magnetic field of physical
shock and vibration or temperature extremes or any
combination of these factors. (also see "magnet
treating".)

**Temperature Coefficient: **A
factor, which describes the reversible change in a magnetic
property with respect to ambient temperature. The magnetic
property will return to its original value when the ambient
temperature returns to normal. Temperature coefficients are
usually expressed as the amount of change per unit pf
temperature.

**Weber
- Wb: **The SI unit of magnetic flux.